![Rusty Russell](/assets/img/avatar_default.png)
Documentation: The Switcher Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
772 lines
26 KiB
C
772 lines
26 KiB
C
/*P:400 This contains run_guest() which actually calls into the Host<->Guest
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* Switcher and analyzes the return, such as determining if the Guest wants the
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* Host to do something. This file also contains useful helper routines, and a
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* couple of non-obvious setup and teardown pieces which were implemented after
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* days of debugging pain. :*/
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#include <linux/module.h>
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#include <linux/stringify.h>
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#include <linux/stddef.h>
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#include <linux/io.h>
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#include <linux/mm.h>
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#include <linux/vmalloc.h>
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#include <linux/cpu.h>
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#include <linux/freezer.h>
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#include <asm/paravirt.h>
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#include <asm/desc.h>
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#include <asm/pgtable.h>
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#include <asm/uaccess.h>
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#include <asm/poll.h>
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#include <asm/highmem.h>
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#include <asm/asm-offsets.h>
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#include <asm/i387.h>
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#include "lg.h"
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/* Found in switcher.S */
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extern char start_switcher_text[], end_switcher_text[], switch_to_guest[];
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extern unsigned long default_idt_entries[];
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/* Every guest maps the core switcher code. */
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#define SHARED_SWITCHER_PAGES \
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DIV_ROUND_UP(end_switcher_text - start_switcher_text, PAGE_SIZE)
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/* Pages for switcher itself, then two pages per cpu */
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#define TOTAL_SWITCHER_PAGES (SHARED_SWITCHER_PAGES + 2 * NR_CPUS)
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/* We map at -4M for ease of mapping into the guest (one PTE page). */
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#define SWITCHER_ADDR 0xFFC00000
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static struct vm_struct *switcher_vma;
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static struct page **switcher_page;
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static int cpu_had_pge;
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static struct {
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unsigned long offset;
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unsigned short segment;
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} lguest_entry;
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/* This One Big lock protects all inter-guest data structures. */
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DEFINE_MUTEX(lguest_lock);
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static DEFINE_PER_CPU(struct lguest *, last_guest);
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/* FIXME: Make dynamic. */
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#define MAX_LGUEST_GUESTS 16
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struct lguest lguests[MAX_LGUEST_GUESTS];
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/* Offset from where switcher.S was compiled to where we've copied it */
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static unsigned long switcher_offset(void)
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{
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return SWITCHER_ADDR - (unsigned long)start_switcher_text;
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}
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/* This cpu's struct lguest_pages. */
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static struct lguest_pages *lguest_pages(unsigned int cpu)
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{
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return &(((struct lguest_pages *)
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(SWITCHER_ADDR + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]);
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}
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/*H:010 We need to set up the Switcher at a high virtual address. Remember the
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* Switcher is a few hundred bytes of assembler code which actually changes the
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* CPU to run the Guest, and then changes back to the Host when a trap or
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* interrupt happens.
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*
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* The Switcher code must be at the same virtual address in the Guest as the
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* Host since it will be running as the switchover occurs.
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*
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* Trying to map memory at a particular address is an unusual thing to do, so
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* it's not a simple one-liner. We also set up the per-cpu parts of the
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* Switcher here.
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*/
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static __init int map_switcher(void)
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{
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int i, err;
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struct page **pagep;
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/*
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* Map the Switcher in to high memory.
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*
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* It turns out that if we choose the address 0xFFC00000 (4MB under the
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* top virtual address), it makes setting up the page tables really
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* easy.
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*/
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/* We allocate an array of "struct page"s. map_vm_area() wants the
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* pages in this form, rather than just an array of pointers. */
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switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
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GFP_KERNEL);
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if (!switcher_page) {
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err = -ENOMEM;
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goto out;
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}
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/* Now we actually allocate the pages. The Guest will see these pages,
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* so we make sure they're zeroed. */
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for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
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unsigned long addr = get_zeroed_page(GFP_KERNEL);
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if (!addr) {
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err = -ENOMEM;
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goto free_some_pages;
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}
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switcher_page[i] = virt_to_page(addr);
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}
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/* Now we reserve the "virtual memory area" we want: 0xFFC00000
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* (SWITCHER_ADDR). We might not get it in theory, but in practice
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* it's worked so far. */
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switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
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VM_ALLOC, SWITCHER_ADDR, VMALLOC_END);
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if (!switcher_vma) {
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err = -ENOMEM;
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printk("lguest: could not map switcher pages high\n");
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goto free_pages;
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}
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/* This code actually sets up the pages we've allocated to appear at
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* SWITCHER_ADDR. map_vm_area() takes the vma we allocated above, the
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* kind of pages we're mapping (kernel pages), and a pointer to our
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* array of struct pages. It increments that pointer, but we don't
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* care. */
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pagep = switcher_page;
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err = map_vm_area(switcher_vma, PAGE_KERNEL, &pagep);
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if (err) {
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printk("lguest: map_vm_area failed: %i\n", err);
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goto free_vma;
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}
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/* Now the switcher is mapped at the right address, we can't fail!
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* Copy in the compiled-in Switcher code (from switcher.S). */
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memcpy(switcher_vma->addr, start_switcher_text,
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end_switcher_text - start_switcher_text);
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/* Most of the switcher.S doesn't care that it's been moved; on Intel,
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* jumps are relative, and it doesn't access any references to external
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* code or data.
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*
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* The only exception is the interrupt handlers in switcher.S: their
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* addresses are placed in a table (default_idt_entries), so we need to
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* update the table with the new addresses. switcher_offset() is a
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* convenience function which returns the distance between the builtin
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* switcher code and the high-mapped copy we just made. */
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for (i = 0; i < IDT_ENTRIES; i++)
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default_idt_entries[i] += switcher_offset();
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/*
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* Set up the Switcher's per-cpu areas.
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*
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* Each CPU gets two pages of its own within the high-mapped region
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* (aka. "struct lguest_pages"). Much of this can be initialized now,
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* but some depends on what Guest we are running (which is set up in
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* copy_in_guest_info()).
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*/
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for_each_possible_cpu(i) {
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/* lguest_pages() returns this CPU's two pages. */
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struct lguest_pages *pages = lguest_pages(i);
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/* This is a convenience pointer to make the code fit one
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* statement to a line. */
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struct lguest_ro_state *state = &pages->state;
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/* The Global Descriptor Table: the Host has a different one
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* for each CPU. We keep a descriptor for the GDT which says
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* where it is and how big it is (the size is actually the last
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* byte, not the size, hence the "-1"). */
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state->host_gdt_desc.size = GDT_SIZE-1;
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state->host_gdt_desc.address = (long)get_cpu_gdt_table(i);
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/* All CPUs on the Host use the same Interrupt Descriptor
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* Table, so we just use store_idt(), which gets this CPU's IDT
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* descriptor. */
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store_idt(&state->host_idt_desc);
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/* The descriptors for the Guest's GDT and IDT can be filled
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* out now, too. We copy the GDT & IDT into ->guest_gdt and
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* ->guest_idt before actually running the Guest. */
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state->guest_idt_desc.size = sizeof(state->guest_idt)-1;
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state->guest_idt_desc.address = (long)&state->guest_idt;
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state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1;
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state->guest_gdt_desc.address = (long)&state->guest_gdt;
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/* We know where we want the stack to be when the Guest enters
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* the switcher: in pages->regs. The stack grows upwards, so
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* we start it at the end of that structure. */
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state->guest_tss.esp0 = (long)(&pages->regs + 1);
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/* And this is the GDT entry to use for the stack: we keep a
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* couple of special LGUEST entries. */
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state->guest_tss.ss0 = LGUEST_DS;
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/* x86 can have a finegrained bitmap which indicates what I/O
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* ports the process can use. We set it to the end of our
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* structure, meaning "none". */
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state->guest_tss.io_bitmap_base = sizeof(state->guest_tss);
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/* Some GDT entries are the same across all Guests, so we can
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* set them up now. */
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setup_default_gdt_entries(state);
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/* Most IDT entries are the same for all Guests, too.*/
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setup_default_idt_entries(state, default_idt_entries);
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/* The Host needs to be able to use the LGUEST segments on this
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* CPU, too, so put them in the Host GDT. */
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get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT;
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get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT;
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}
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/* In the Switcher, we want the %cs segment register to use the
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* LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so
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* it will be undisturbed when we switch. To change %cs and jump we
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* need this structure to feed to Intel's "lcall" instruction. */
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lguest_entry.offset = (long)switch_to_guest + switcher_offset();
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lguest_entry.segment = LGUEST_CS;
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printk(KERN_INFO "lguest: mapped switcher at %p\n",
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switcher_vma->addr);
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/* And we succeeded... */
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return 0;
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free_vma:
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vunmap(switcher_vma->addr);
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free_pages:
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i = TOTAL_SWITCHER_PAGES;
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free_some_pages:
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for (--i; i >= 0; i--)
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__free_pages(switcher_page[i], 0);
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kfree(switcher_page);
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out:
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return err;
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}
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/*:*/
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/* Cleaning up the mapping when the module is unloaded is almost...
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* too easy. */
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static void unmap_switcher(void)
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{
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unsigned int i;
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/* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
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vunmap(switcher_vma->addr);
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/* Now we just need to free the pages we copied the switcher into */
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for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
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__free_pages(switcher_page[i], 0);
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}
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/*H:130 Our Guest is usually so well behaved; it never tries to do things it
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* isn't allowed to. Unfortunately, "struct paravirt_ops" isn't quite
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* complete, because it doesn't contain replacements for the Intel I/O
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* instructions. As a result, the Guest sometimes fumbles across one during
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* the boot process as it probes for various things which are usually attached
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* to a PC.
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*
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* When the Guest uses one of these instructions, we get trap #13 (General
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* Protection Fault) and come here. We see if it's one of those troublesome
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* instructions and skip over it. We return true if we did. */
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static int emulate_insn(struct lguest *lg)
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{
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u8 insn;
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unsigned int insnlen = 0, in = 0, shift = 0;
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/* The eip contains the *virtual* address of the Guest's instruction:
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* guest_pa just subtracts the Guest's page_offset. */
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unsigned long physaddr = guest_pa(lg, lg->regs->eip);
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/* The guest_pa() function only works for Guest kernel addresses, but
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* that's all we're trying to do anyway. */
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if (lg->regs->eip < lg->page_offset)
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return 0;
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/* Decoding x86 instructions is icky. */
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lgread(lg, &insn, physaddr, 1);
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/* 0x66 is an "operand prefix". It means it's using the upper 16 bits
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of the eax register. */
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if (insn == 0x66) {
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shift = 16;
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/* The instruction is 1 byte so far, read the next byte. */
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insnlen = 1;
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lgread(lg, &insn, physaddr + insnlen, 1);
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}
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/* We can ignore the lower bit for the moment and decode the 4 opcodes
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* we need to emulate. */
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switch (insn & 0xFE) {
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case 0xE4: /* in <next byte>,%al */
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insnlen += 2;
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in = 1;
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break;
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case 0xEC: /* in (%dx),%al */
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insnlen += 1;
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in = 1;
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break;
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case 0xE6: /* out %al,<next byte> */
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insnlen += 2;
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break;
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case 0xEE: /* out %al,(%dx) */
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insnlen += 1;
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break;
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default:
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/* OK, we don't know what this is, can't emulate. */
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return 0;
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}
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/* If it was an "IN" instruction, they expect the result to be read
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* into %eax, so we change %eax. We always return all-ones, which
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* traditionally means "there's nothing there". */
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if (in) {
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/* Lower bit tells is whether it's a 16 or 32 bit access */
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if (insn & 0x1)
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lg->regs->eax = 0xFFFFFFFF;
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else
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lg->regs->eax |= (0xFFFF << shift);
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}
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/* Finally, we've "done" the instruction, so move past it. */
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lg->regs->eip += insnlen;
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/* Success! */
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return 1;
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}
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/*:*/
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/*L:305
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* Dealing With Guest Memory.
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*
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* When the Guest gives us (what it thinks is) a physical address, we can use
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* the normal copy_from_user() & copy_to_user() on that address: remember,
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* Guest physical == Launcher virtual.
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*
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* But we can't trust the Guest: it might be trying to access the Launcher
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* code. We have to check that the range is below the pfn_limit the Launcher
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* gave us. We have to make sure that addr + len doesn't give us a false
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* positive by overflowing, too. */
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int lguest_address_ok(const struct lguest *lg,
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unsigned long addr, unsigned long len)
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{
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return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
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}
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/* This is a convenient routine to get a 32-bit value from the Guest (a very
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* common operation). Here we can see how useful the kill_lguest() routine we
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* met in the Launcher can be: we return a random value (0) instead of needing
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* to return an error. */
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u32 lgread_u32(struct lguest *lg, unsigned long addr)
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{
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u32 val = 0;
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/* Don't let them access lguest binary. */
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if (!lguest_address_ok(lg, addr, sizeof(val))
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|| get_user(val, (u32 __user *)addr) != 0)
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kill_guest(lg, "bad read address %#lx", addr);
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return val;
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}
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/* Same thing for writing a value. */
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void lgwrite_u32(struct lguest *lg, unsigned long addr, u32 val)
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{
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if (!lguest_address_ok(lg, addr, sizeof(val))
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|| put_user(val, (u32 __user *)addr) != 0)
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kill_guest(lg, "bad write address %#lx", addr);
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}
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/* This routine is more generic, and copies a range of Guest bytes into a
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* buffer. If the copy_from_user() fails, we fill the buffer with zeroes, so
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* the caller doesn't end up using uninitialized kernel memory. */
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void lgread(struct lguest *lg, void *b, unsigned long addr, unsigned bytes)
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{
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if (!lguest_address_ok(lg, addr, bytes)
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|| copy_from_user(b, (void __user *)addr, bytes) != 0) {
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/* copy_from_user should do this, but as we rely on it... */
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memset(b, 0, bytes);
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kill_guest(lg, "bad read address %#lx len %u", addr, bytes);
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}
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}
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/* Similarly, our generic routine to copy into a range of Guest bytes. */
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void lgwrite(struct lguest *lg, unsigned long addr, const void *b,
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unsigned bytes)
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{
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if (!lguest_address_ok(lg, addr, bytes)
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|| copy_to_user((void __user *)addr, b, bytes) != 0)
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kill_guest(lg, "bad write address %#lx len %u", addr, bytes);
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}
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/* (end of memory access helper routines) :*/
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static void set_ts(void)
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{
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u32 cr0;
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cr0 = read_cr0();
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if (!(cr0 & 8))
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write_cr0(cr0|8);
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}
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/*S:010
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* We are getting close to the Switcher.
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*
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* Remember that each CPU has two pages which are visible to the Guest when it
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* runs on that CPU. This has to contain the state for that Guest: we copy the
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* state in just before we run the Guest.
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*
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* Each Guest has "changed" flags which indicate what has changed in the Guest
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* since it last ran. We saw this set in interrupts_and_traps.c and
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* segments.c.
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*/
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static void copy_in_guest_info(struct lguest *lg, struct lguest_pages *pages)
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{
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/* Copying all this data can be quite expensive. We usually run the
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* same Guest we ran last time (and that Guest hasn't run anywhere else
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* meanwhile). If that's not the case, we pretend everything in the
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* Guest has changed. */
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if (__get_cpu_var(last_guest) != lg || lg->last_pages != pages) {
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__get_cpu_var(last_guest) = lg;
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lg->last_pages = pages;
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lg->changed = CHANGED_ALL;
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}
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/* These copies are pretty cheap, so we do them unconditionally: */
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/* Save the current Host top-level page directory. */
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pages->state.host_cr3 = __pa(current->mm->pgd);
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/* Set up the Guest's page tables to see this CPU's pages (and no
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* other CPU's pages). */
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map_switcher_in_guest(lg, pages);
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/* Set up the two "TSS" members which tell the CPU what stack to use
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* for traps which do directly into the Guest (ie. traps at privilege
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* level 1). */
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pages->state.guest_tss.esp1 = lg->esp1;
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pages->state.guest_tss.ss1 = lg->ss1;
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/* Copy direct-to-Guest trap entries. */
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if (lg->changed & CHANGED_IDT)
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copy_traps(lg, pages->state.guest_idt, default_idt_entries);
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/* Copy all GDT entries which the Guest can change. */
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if (lg->changed & CHANGED_GDT)
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copy_gdt(lg, pages->state.guest_gdt);
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/* If only the TLS entries have changed, copy them. */
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else if (lg->changed & CHANGED_GDT_TLS)
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copy_gdt_tls(lg, pages->state.guest_gdt);
|
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|
|
/* Mark the Guest as unchanged for next time. */
|
|
lg->changed = 0;
|
|
}
|
|
|
|
/* Finally: the code to actually call into the Switcher to run the Guest. */
|
|
static void run_guest_once(struct lguest *lg, struct lguest_pages *pages)
|
|
{
|
|
/* This is a dummy value we need for GCC's sake. */
|
|
unsigned int clobber;
|
|
|
|
/* Copy the guest-specific information into this CPU's "struct
|
|
* lguest_pages". */
|
|
copy_in_guest_info(lg, pages);
|
|
|
|
/* Now: we push the "eflags" register on the stack, then do an "lcall".
|
|
* This is how we change from using the kernel code segment to using
|
|
* the dedicated lguest code segment, as well as jumping into the
|
|
* Switcher.
|
|
*
|
|
* The lcall also pushes the old code segment (KERNEL_CS) onto the
|
|
* stack, then the address of this call. This stack layout happens to
|
|
* exactly match the stack of an interrupt... */
|
|
asm volatile("pushf; lcall *lguest_entry"
|
|
/* This is how we tell GCC that %eax ("a") and %ebx ("b")
|
|
* are changed by this routine. The "=" means output. */
|
|
: "=a"(clobber), "=b"(clobber)
|
|
/* %eax contains the pages pointer. ("0" refers to the
|
|
* 0-th argument above, ie "a"). %ebx contains the
|
|
* physical address of the Guest's top-level page
|
|
* directory. */
|
|
: "0"(pages), "1"(__pa(lg->pgdirs[lg->pgdidx].pgdir))
|
|
/* We tell gcc that all these registers could change,
|
|
* which means we don't have to save and restore them in
|
|
* the Switcher. */
|
|
: "memory", "%edx", "%ecx", "%edi", "%esi");
|
|
}
|
|
/*:*/
|
|
|
|
/*H:030 Let's jump straight to the the main loop which runs the Guest.
|
|
* Remember, this is called by the Launcher reading /dev/lguest, and we keep
|
|
* going around and around until something interesting happens. */
|
|
int run_guest(struct lguest *lg, unsigned long __user *user)
|
|
{
|
|
/* We stop running once the Guest is dead. */
|
|
while (!lg->dead) {
|
|
/* We need to initialize this, otherwise gcc complains. It's
|
|
* not (yet) clever enough to see that it's initialized when we
|
|
* need it. */
|
|
unsigned int cr2 = 0; /* Damn gcc */
|
|
|
|
/* First we run any hypercalls the Guest wants done: either in
|
|
* the hypercall ring in "struct lguest_data", or directly by
|
|
* using int 31 (LGUEST_TRAP_ENTRY). */
|
|
do_hypercalls(lg);
|
|
/* It's possible the Guest did a SEND_DMA hypercall to the
|
|
* Launcher, in which case we return from the read() now. */
|
|
if (lg->dma_is_pending) {
|
|
if (put_user(lg->pending_dma, user) ||
|
|
put_user(lg->pending_key, user+1))
|
|
return -EFAULT;
|
|
return sizeof(unsigned long)*2;
|
|
}
|
|
|
|
/* Check for signals */
|
|
if (signal_pending(current))
|
|
return -ERESTARTSYS;
|
|
|
|
/* If Waker set break_out, return to Launcher. */
|
|
if (lg->break_out)
|
|
return -EAGAIN;
|
|
|
|
/* Check if there are any interrupts which can be delivered
|
|
* now: if so, this sets up the hander to be executed when we
|
|
* next run the Guest. */
|
|
maybe_do_interrupt(lg);
|
|
|
|
/* All long-lived kernel loops need to check with this horrible
|
|
* thing called the freezer. If the Host is trying to suspend,
|
|
* it stops us. */
|
|
try_to_freeze();
|
|
|
|
/* Just make absolutely sure the Guest is still alive. One of
|
|
* those hypercalls could have been fatal, for example. */
|
|
if (lg->dead)
|
|
break;
|
|
|
|
/* If the Guest asked to be stopped, we sleep. The Guest's
|
|
* clock timer or LHCALL_BREAK from the Waker will wake us. */
|
|
if (lg->halted) {
|
|
set_current_state(TASK_INTERRUPTIBLE);
|
|
schedule();
|
|
continue;
|
|
}
|
|
|
|
/* OK, now we're ready to jump into the Guest. First we put up
|
|
* the "Do Not Disturb" sign: */
|
|
local_irq_disable();
|
|
|
|
/* Remember the awfully-named TS bit? If the Guest has asked
|
|
* to set it we set it now, so we can trap and pass that trap
|
|
* to the Guest if it uses the FPU. */
|
|
if (lg->ts)
|
|
set_ts();
|
|
|
|
/* SYSENTER is an optimized way of doing system calls. We
|
|
* can't allow it because it always jumps to privilege level 0.
|
|
* A normal Guest won't try it because we don't advertise it in
|
|
* CPUID, but a malicious Guest (or malicious Guest userspace
|
|
* program) could, so we tell the CPU to disable it before
|
|
* running the Guest. */
|
|
if (boot_cpu_has(X86_FEATURE_SEP))
|
|
wrmsr(MSR_IA32_SYSENTER_CS, 0, 0);
|
|
|
|
/* Now we actually run the Guest. It will pop back out when
|
|
* something interesting happens, and we can examine its
|
|
* registers to see what it was doing. */
|
|
run_guest_once(lg, lguest_pages(raw_smp_processor_id()));
|
|
|
|
/* The "regs" pointer contains two extra entries which are not
|
|
* really registers: a trap number which says what interrupt or
|
|
* trap made the switcher code come back, and an error code
|
|
* which some traps set. */
|
|
|
|
/* If the Guest page faulted, then the cr2 register will tell
|
|
* us the bad virtual address. We have to grab this now,
|
|
* because once we re-enable interrupts an interrupt could
|
|
* fault and thus overwrite cr2, or we could even move off to a
|
|
* different CPU. */
|
|
if (lg->regs->trapnum == 14)
|
|
cr2 = read_cr2();
|
|
/* Similarly, if we took a trap because the Guest used the FPU,
|
|
* we have to restore the FPU it expects to see. */
|
|
else if (lg->regs->trapnum == 7)
|
|
math_state_restore();
|
|
|
|
/* Restore SYSENTER if it's supposed to be on. */
|
|
if (boot_cpu_has(X86_FEATURE_SEP))
|
|
wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
|
|
|
|
/* Now we're ready to be interrupted or moved to other CPUs */
|
|
local_irq_enable();
|
|
|
|
/* OK, so what happened? */
|
|
switch (lg->regs->trapnum) {
|
|
case 13: /* We've intercepted a GPF. */
|
|
/* Check if this was one of those annoying IN or OUT
|
|
* instructions which we need to emulate. If so, we
|
|
* just go back into the Guest after we've done it. */
|
|
if (lg->regs->errcode == 0) {
|
|
if (emulate_insn(lg))
|
|
continue;
|
|
}
|
|
break;
|
|
case 14: /* We've intercepted a page fault. */
|
|
/* The Guest accessed a virtual address that wasn't
|
|
* mapped. This happens a lot: we don't actually set
|
|
* up most of the page tables for the Guest at all when
|
|
* we start: as it runs it asks for more and more, and
|
|
* we set them up as required. In this case, we don't
|
|
* even tell the Guest that the fault happened.
|
|
*
|
|
* The errcode tells whether this was a read or a
|
|
* write, and whether kernel or userspace code. */
|
|
if (demand_page(lg, cr2, lg->regs->errcode))
|
|
continue;
|
|
|
|
/* OK, it's really not there (or not OK): the Guest
|
|
* needs to know. We write out the cr2 value so it
|
|
* knows where the fault occurred.
|
|
*
|
|
* Note that if the Guest were really messed up, this
|
|
* could happen before it's done the INITIALIZE
|
|
* hypercall, so lg->lguest_data will be NULL, so
|
|
* &lg->lguest_data->cr2 will be address 8. Writing
|
|
* into that address won't hurt the Host at all,
|
|
* though. */
|
|
if (put_user(cr2, &lg->lguest_data->cr2))
|
|
kill_guest(lg, "Writing cr2");
|
|
break;
|
|
case 7: /* We've intercepted a Device Not Available fault. */
|
|
/* If the Guest doesn't want to know, we already
|
|
* restored the Floating Point Unit, so we just
|
|
* continue without telling it. */
|
|
if (!lg->ts)
|
|
continue;
|
|
break;
|
|
case 32 ... 255:
|
|
/* These values mean a real interrupt occurred, in
|
|
* which case the Host handler has already been run.
|
|
* We just do a friendly check if another process
|
|
* should now be run, then fall through to loop
|
|
* around: */
|
|
cond_resched();
|
|
case LGUEST_TRAP_ENTRY: /* Handled at top of loop */
|
|
continue;
|
|
}
|
|
|
|
/* If we get here, it's a trap the Guest wants to know
|
|
* about. */
|
|
if (deliver_trap(lg, lg->regs->trapnum))
|
|
continue;
|
|
|
|
/* If the Guest doesn't have a handler (either it hasn't
|
|
* registered any yet, or it's one of the faults we don't let
|
|
* it handle), it dies with a cryptic error message. */
|
|
kill_guest(lg, "unhandled trap %li at %#lx (%#lx)",
|
|
lg->regs->trapnum, lg->regs->eip,
|
|
lg->regs->trapnum == 14 ? cr2 : lg->regs->errcode);
|
|
}
|
|
/* The Guest is dead => "No such file or directory" */
|
|
return -ENOENT;
|
|
}
|
|
|
|
/* Now we can look at each of the routines this calls, in increasing order of
|
|
* complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(),
|
|
* deliver_trap() and demand_page(). After all those, we'll be ready to
|
|
* examine the Switcher, and our philosophical understanding of the Host/Guest
|
|
* duality will be complete. :*/
|
|
|
|
int find_free_guest(void)
|
|
{
|
|
unsigned int i;
|
|
for (i = 0; i < MAX_LGUEST_GUESTS; i++)
|
|
if (!lguests[i].tsk)
|
|
return i;
|
|
return -1;
|
|
}
|
|
|
|
static void adjust_pge(void *on)
|
|
{
|
|
if (on)
|
|
write_cr4(read_cr4() | X86_CR4_PGE);
|
|
else
|
|
write_cr4(read_cr4() & ~X86_CR4_PGE);
|
|
}
|
|
|
|
/*H:000
|
|
* Welcome to the Host!
|
|
*
|
|
* By this point your brain has been tickled by the Guest code and numbed by
|
|
* the Launcher code; prepare for it to be stretched by the Host code. This is
|
|
* the heart. Let's begin at the initialization routine for the Host's lg
|
|
* module.
|
|
*/
|
|
static int __init init(void)
|
|
{
|
|
int err;
|
|
|
|
/* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */
|
|
if (paravirt_enabled()) {
|
|
printk("lguest is afraid of %s\n", paravirt_ops.name);
|
|
return -EPERM;
|
|
}
|
|
|
|
/* First we put the Switcher up in very high virtual memory. */
|
|
err = map_switcher();
|
|
if (err)
|
|
return err;
|
|
|
|
/* Now we set up the pagetable implementation for the Guests. */
|
|
err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
|
|
if (err) {
|
|
unmap_switcher();
|
|
return err;
|
|
}
|
|
|
|
/* The I/O subsystem needs some things initialized. */
|
|
lguest_io_init();
|
|
|
|
/* /dev/lguest needs to be registered. */
|
|
err = lguest_device_init();
|
|
if (err) {
|
|
free_pagetables();
|
|
unmap_switcher();
|
|
return err;
|
|
}
|
|
|
|
/* Finally, we need to turn off "Page Global Enable". PGE is an
|
|
* optimization where page table entries are specially marked to show
|
|
* they never change. The Host kernel marks all the kernel pages this
|
|
* way because it's always present, even when userspace is running.
|
|
*
|
|
* Lguest breaks this: unbeknownst to the rest of the Host kernel, we
|
|
* switch to the Guest kernel. If you don't disable this on all CPUs,
|
|
* you'll get really weird bugs that you'll chase for two days.
|
|
*
|
|
* I used to turn PGE off every time we switched to the Guest and back
|
|
* on when we return, but that slowed the Switcher down noticibly. */
|
|
|
|
/* We don't need the complexity of CPUs coming and going while we're
|
|
* doing this. */
|
|
lock_cpu_hotplug();
|
|
if (cpu_has_pge) { /* We have a broader idea of "global". */
|
|
/* Remember that this was originally set (for cleanup). */
|
|
cpu_had_pge = 1;
|
|
/* adjust_pge is a helper function which sets or unsets the PGE
|
|
* bit on its CPU, depending on the argument (0 == unset). */
|
|
on_each_cpu(adjust_pge, (void *)0, 0, 1);
|
|
/* Turn off the feature in the global feature set. */
|
|
clear_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability);
|
|
}
|
|
unlock_cpu_hotplug();
|
|
|
|
/* All good! */
|
|
return 0;
|
|
}
|
|
|
|
/* Cleaning up is just the same code, backwards. With a little French. */
|
|
static void __exit fini(void)
|
|
{
|
|
lguest_device_remove();
|
|
free_pagetables();
|
|
unmap_switcher();
|
|
|
|
/* If we had PGE before we started, turn it back on now. */
|
|
lock_cpu_hotplug();
|
|
if (cpu_had_pge) {
|
|
set_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability);
|
|
/* adjust_pge's argument "1" means set PGE. */
|
|
on_each_cpu(adjust_pge, (void *)1, 0, 1);
|
|
}
|
|
unlock_cpu_hotplug();
|
|
}
|
|
|
|
/* The Host side of lguest can be a module. This is a nice way for people to
|
|
* play with it. */
|
|
module_init(init);
|
|
module_exit(fini);
|
|
MODULE_LICENSE("GPL");
|
|
MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
|