![Rusty Russell](/assets/img/avatar_default.png)
Documentation: The FIXMEs 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>
627 lines
21 KiB
C
627 lines
21 KiB
C
/*P:300 The I/O mechanism in lguest is simple yet flexible, allowing the Guest
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* to talk to the Launcher or directly to another Guest. It uses familiar
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* concepts of DMA and interrupts, plus some neat code stolen from
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* futexes... :*/
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/* Copyright (C) 2006 Rusty Russell IBM Corporation
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <linux/types.h>
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#include <linux/futex.h>
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#include <linux/jhash.h>
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#include <linux/mm.h>
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#include <linux/highmem.h>
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#include <linux/uaccess.h>
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#include "lg.h"
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/*L:300
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* I/O
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*
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* Getting data in and out of the Guest is quite an art. There are numerous
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* ways to do it, and they all suck differently. We try to keep things fairly
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* close to "real" hardware so our Guest's drivers don't look like an alien
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* visitation in the middle of the Linux code, and yet make sure that Guests
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* can talk directly to other Guests, not just the Launcher.
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*
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* To do this, the Guest gives us a key when it binds or sends DMA buffers.
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* The key corresponds to a "physical" address inside the Guest (ie. a virtual
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* address inside the Launcher process). We don't, however, use this key
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* directly.
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*
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* We want Guests which share memory to be able to DMA to each other: two
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* Launchers can mmap memory the same file, then the Guests can communicate.
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* Fortunately, the futex code provides us with a way to get a "union
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* futex_key" corresponding to the memory lying at a virtual address: if the
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* two processes share memory, the "union futex_key" for that memory will match
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* even if the memory is mapped at different addresses in each. So we always
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* convert the keys to "union futex_key"s to compare them.
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*
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* Before we dive into this though, we need to look at another set of helper
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* routines used throughout the Host kernel code to access Guest memory.
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:*/
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static struct list_head dma_hash[61];
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/* An unfortunate side effect of the Linux double-linked list implementation is
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* that there's no good way to statically initialize an array of linked
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* lists. */
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void lguest_io_init(void)
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{
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unsigned int i;
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for (i = 0; i < ARRAY_SIZE(dma_hash); i++)
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INIT_LIST_HEAD(&dma_hash[i]);
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}
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/* FIXME: allow multi-page lengths. */
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static int check_dma_list(struct lguest *lg, const struct lguest_dma *dma)
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{
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unsigned int i;
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for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
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if (!dma->len[i])
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return 1;
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if (!lguest_address_ok(lg, dma->addr[i], dma->len[i]))
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goto kill;
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if (dma->len[i] > PAGE_SIZE)
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goto kill;
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/* We could do over a page, but is it worth it? */
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if ((dma->addr[i] % PAGE_SIZE) + dma->len[i] > PAGE_SIZE)
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goto kill;
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}
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return 1;
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kill:
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kill_guest(lg, "bad DMA entry: %u@%#lx", dma->len[i], dma->addr[i]);
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return 0;
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}
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/*L:330 This is our hash function, using the wonderful Jenkins hash.
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*
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* The futex key is a union with three parts: an unsigned long word, a pointer,
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* and an int "offset". We could use jhash_2words() which takes three u32s.
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* (Ok, the hash functions are great: the naming sucks though).
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*
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* It's nice to be portable to 64-bit platforms, so we use the more generic
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* jhash2(), which takes an array of u32, the number of u32s, and an initial
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* u32 to roll in. This is uglier, but breaks down to almost the same code on
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* 32-bit platforms like this one.
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*
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* We want a position in the array, so we modulo ARRAY_SIZE(dma_hash) (ie. 61).
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*/
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static unsigned int hash(const union futex_key *key)
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{
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return jhash2((u32*)&key->both.word,
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(sizeof(key->both.word)+sizeof(key->both.ptr))/4,
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key->both.offset)
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% ARRAY_SIZE(dma_hash);
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}
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/* This is a convenience routine to compare two keys. It's a much bemoaned C
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* weakness that it doesn't allow '==' on structures or unions, so we have to
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* open-code it like this. */
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static inline int key_eq(const union futex_key *a, const union futex_key *b)
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{
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return (a->both.word == b->both.word
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&& a->both.ptr == b->both.ptr
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&& a->both.offset == b->both.offset);
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}
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/*L:360 OK, when we need to actually free up a Guest's DMA array we do several
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* things, so we have a convenient function to do it.
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*
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* The caller must hold a read lock on dmainfo owner's current->mm->mmap_sem
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* for the drop_futex_key_refs(). */
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static void unlink_dma(struct lguest_dma_info *dmainfo)
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{
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/* You locked this too, right? */
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BUG_ON(!mutex_is_locked(&lguest_lock));
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/* This is how we know that the entry is free. */
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dmainfo->interrupt = 0;
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/* Remove it from the hash table. */
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list_del(&dmainfo->list);
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/* Drop the references we were holding (to the inode or mm). */
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drop_futex_key_refs(&dmainfo->key);
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}
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/*L:350 This is the routine which we call when the Guest asks to unregister a
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* DMA array attached to a given key. Returns true if the array was found. */
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static int unbind_dma(struct lguest *lg,
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const union futex_key *key,
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unsigned long dmas)
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{
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int i, ret = 0;
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/* We don't bother with the hash table, just look through all this
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* Guest's DMA arrays. */
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for (i = 0; i < LGUEST_MAX_DMA; i++) {
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/* In theory it could have more than one array on the same key,
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* or one array on multiple keys, so we check both */
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if (key_eq(key, &lg->dma[i].key) && dmas == lg->dma[i].dmas) {
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unlink_dma(&lg->dma[i]);
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ret = 1;
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break;
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}
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}
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return ret;
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}
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/*L:340 BIND_DMA: this is the hypercall which sets up an array of "struct
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* lguest_dma" for receiving I/O.
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*
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* The Guest wants to bind an array of "struct lguest_dma"s to a particular key
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* to receive input. This only happens when the Guest is setting up a new
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* device, so it doesn't have to be very fast.
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*
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* It returns 1 on a successful registration (it can fail if we hit the limit
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* of registrations for this Guest).
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*/
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int bind_dma(struct lguest *lg,
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unsigned long ukey, unsigned long dmas, u16 numdmas, u8 interrupt)
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{
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unsigned int i;
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int ret = 0;
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union futex_key key;
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/* Futex code needs the mmap_sem. */
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struct rw_semaphore *fshared = ¤t->mm->mmap_sem;
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/* Invalid interrupt? (We could kill the guest here). */
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if (interrupt >= LGUEST_IRQS)
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return 0;
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/* We need to grab the Big Lguest Lock, because other Guests may be
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* trying to look through this Guest's DMAs to send something while
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* we're doing this. */
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mutex_lock(&lguest_lock);
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down_read(fshared);
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if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) {
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kill_guest(lg, "bad dma key %#lx", ukey);
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goto unlock;
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}
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/* We want to keep this key valid once we drop mmap_sem, so we have to
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* hold a reference. */
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get_futex_key_refs(&key);
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/* If the Guest specified an interrupt of 0, that means they want to
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* unregister this array of "struct lguest_dma"s. */
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if (interrupt == 0)
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ret = unbind_dma(lg, &key, dmas);
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else {
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/* Look through this Guest's dma array for an unused entry. */
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for (i = 0; i < LGUEST_MAX_DMA; i++) {
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/* If the interrupt is non-zero, the entry is already
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* used. */
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if (lg->dma[i].interrupt)
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continue;
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/* OK, a free one! Fill on our details. */
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lg->dma[i].dmas = dmas;
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lg->dma[i].num_dmas = numdmas;
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lg->dma[i].next_dma = 0;
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lg->dma[i].key = key;
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lg->dma[i].guestid = lg->guestid;
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lg->dma[i].interrupt = interrupt;
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/* Now we add it to the hash table: the position
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* depends on the futex key that we got. */
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list_add(&lg->dma[i].list, &dma_hash[hash(&key)]);
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/* Success! */
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ret = 1;
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goto unlock;
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}
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}
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/* If we didn't find a slot to put the key in, drop the reference
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* again. */
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drop_futex_key_refs(&key);
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unlock:
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/* Unlock and out. */
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up_read(fshared);
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mutex_unlock(&lguest_lock);
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return ret;
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}
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/*L:385 Note that our routines to access a different Guest's memory are called
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* lgread_other() and lgwrite_other(): these names emphasize that they are only
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* used when the Guest is *not* the current Guest.
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*
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* The interface for copying from another process's memory is called
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* access_process_vm(), with a final argument of 0 for a read, and 1 for a
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* write.
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*
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* We need lgread_other() to read the destination Guest's "struct lguest_dma"
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* array. */
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static int lgread_other(struct lguest *lg,
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void *buf, u32 addr, unsigned bytes)
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{
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if (!lguest_address_ok(lg, addr, bytes)
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|| access_process_vm(lg->tsk, addr, buf, bytes, 0) != bytes) {
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memset(buf, 0, bytes);
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kill_guest(lg, "bad address in registered DMA struct");
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return 0;
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}
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return 1;
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}
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/* "lgwrite()" to another Guest: used to update the destination "used_len" once
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* we've transferred data into the buffer. */
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static int lgwrite_other(struct lguest *lg, u32 addr,
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const void *buf, unsigned bytes)
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{
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if (!lguest_address_ok(lg, addr, bytes)
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|| (access_process_vm(lg->tsk, addr, (void *)buf, bytes, 1)
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!= bytes)) {
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kill_guest(lg, "bad address writing to registered DMA");
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return 0;
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}
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return 1;
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}
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/*L:400 This is the generic engine which copies from a source "struct
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* lguest_dma" from this Guest into another Guest's "struct lguest_dma". The
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* destination Guest's pages have already been mapped, as contained in the
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* pages array.
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*
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* If you're wondering if there's a nice "copy from one process to another"
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* routine, so was I. But Linux isn't really set up to copy between two
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* unrelated processes, so we have to write it ourselves.
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*/
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static u32 copy_data(struct lguest *srclg,
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const struct lguest_dma *src,
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const struct lguest_dma *dst,
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struct page *pages[])
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{
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unsigned int totlen, si, di, srcoff, dstoff;
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void *maddr = NULL;
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/* We return the total length transferred. */
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totlen = 0;
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/* We keep indexes into the source and destination "struct lguest_dma",
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* and an offset within each region. */
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si = di = 0;
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srcoff = dstoff = 0;
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/* We loop until the source or destination is exhausted. */
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while (si < LGUEST_MAX_DMA_SECTIONS && src->len[si]
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&& di < LGUEST_MAX_DMA_SECTIONS && dst->len[di]) {
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/* We can only transfer the rest of the src buffer, or as much
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* as will fit into the destination buffer. */
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u32 len = min(src->len[si] - srcoff, dst->len[di] - dstoff);
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/* For systems using "highmem" we need to use kmap() to access
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* the page we want. We often use the same page over and over,
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* so rather than kmap() it on every loop, we set the maddr
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* pointer to NULL when we need to move to the next
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* destination page. */
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if (!maddr)
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maddr = kmap(pages[di]);
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/* Copy directly from (this Guest's) source address to the
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* destination Guest's kmap()ed buffer. Note that maddr points
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* to the start of the page: we need to add the offset of the
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* destination address and offset within the buffer. */
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/* FIXME: This is not completely portable. I looked at
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* copy_to_user_page(), and some arch's seem to need special
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* flushes. x86 is fine. */
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if (copy_from_user(maddr + (dst->addr[di] + dstoff)%PAGE_SIZE,
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(void __user *)src->addr[si], len) != 0) {
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/* If a copy failed, it's the source's fault. */
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kill_guest(srclg, "bad address in sending DMA");
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totlen = 0;
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break;
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}
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/* Increment the total and src & dst offsets */
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totlen += len;
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srcoff += len;
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dstoff += len;
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/* Presumably we reached the end of the src or dest buffers: */
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if (srcoff == src->len[si]) {
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/* Move to the next buffer at offset 0 */
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si++;
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srcoff = 0;
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}
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if (dstoff == dst->len[di]) {
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/* We need to unmap that destination page and reset
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* maddr ready for the next one. */
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kunmap(pages[di]);
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maddr = NULL;
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di++;
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dstoff = 0;
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}
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}
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/* If we still had a page mapped at the end, unmap now. */
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if (maddr)
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kunmap(pages[di]);
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return totlen;
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}
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/*L:390 This is how we transfer a "struct lguest_dma" from the source Guest
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* (the current Guest which called SEND_DMA) to another Guest. */
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static u32 do_dma(struct lguest *srclg, const struct lguest_dma *src,
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struct lguest *dstlg, const struct lguest_dma *dst)
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{
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int i;
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u32 ret;
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struct page *pages[LGUEST_MAX_DMA_SECTIONS];
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/* We check that both source and destination "struct lguest_dma"s are
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* within the bounds of the source and destination Guests */
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if (!check_dma_list(dstlg, dst) || !check_dma_list(srclg, src))
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return 0;
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/* We need to map the pages which correspond to each parts of
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* destination buffer. */
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for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) {
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if (dst->len[i] == 0)
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break;
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/* get_user_pages() is a complicated function, especially since
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* we only want a single page. But it works, and returns the
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* number of pages. Note that we're holding the destination's
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* mmap_sem, as get_user_pages() requires. */
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if (get_user_pages(dstlg->tsk, dstlg->mm,
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dst->addr[i], 1, 1, 1, pages+i, NULL)
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!= 1) {
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/* This means the destination gave us a bogus buffer */
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kill_guest(dstlg, "Error mapping DMA pages");
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ret = 0;
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goto drop_pages;
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}
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}
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/* Now copy the data until we run out of src or dst. */
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ret = copy_data(srclg, src, dst, pages);
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drop_pages:
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while (--i >= 0)
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put_page(pages[i]);
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return ret;
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}
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/*L:380 Transferring data from one Guest to another is not as simple as I'd
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* like. We've found the "struct lguest_dma_info" bound to the same address as
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* the send, we need to copy into it.
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*
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* This function returns true if the destination array was empty. */
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static int dma_transfer(struct lguest *srclg,
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unsigned long udma,
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struct lguest_dma_info *dst)
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{
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struct lguest_dma dst_dma, src_dma;
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struct lguest *dstlg;
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u32 i, dma = 0;
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/* From the "struct lguest_dma_info" we found in the hash, grab the
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* Guest. */
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dstlg = &lguests[dst->guestid];
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/* Read in the source "struct lguest_dma" handed to SEND_DMA. */
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lgread(srclg, &src_dma, udma, sizeof(src_dma));
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/* We need the destination's mmap_sem, and we already hold the source's
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* mmap_sem for the futex key lookup. Normally this would suggest that
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* we could deadlock if the destination Guest was trying to send to
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* this source Guest at the same time, which is another reason that all
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* I/O is done under the big lguest_lock. */
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down_read(&dstlg->mm->mmap_sem);
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/* Look through the destination DMA array for an available buffer. */
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for (i = 0; i < dst->num_dmas; i++) {
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/* We keep a "next_dma" pointer which often helps us avoid
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* looking at lots of previously-filled entries. */
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dma = (dst->next_dma + i) % dst->num_dmas;
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if (!lgread_other(dstlg, &dst_dma,
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dst->dmas + dma * sizeof(struct lguest_dma),
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sizeof(dst_dma))) {
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goto fail;
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}
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if (!dst_dma.used_len)
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break;
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}
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/* If we found a buffer, we do the actual data copy. */
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if (i != dst->num_dmas) {
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unsigned long used_lenp;
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unsigned int ret;
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ret = do_dma(srclg, &src_dma, dstlg, &dst_dma);
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/* Put used length in the source "struct lguest_dma"'s used_len
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* field. It's a little tricky to figure out where that is,
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* though. */
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lgwrite_u32(srclg,
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udma+offsetof(struct lguest_dma, used_len), ret);
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/* Tranferring 0 bytes is OK if the source buffer was empty. */
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if (ret == 0 && src_dma.len[0] != 0)
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goto fail;
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/* The destination Guest might be running on a different CPU:
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* we have to make sure that it will see the "used_len" field
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* change to non-zero *after* it sees the data we copied into
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* the buffer. Hence a write memory barrier. */
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wmb();
|
|
/* Figuring out where the destination's used_len field for this
|
|
* "struct lguest_dma" in the array is also a little ugly. */
|
|
used_lenp = dst->dmas
|
|
+ dma * sizeof(struct lguest_dma)
|
|
+ offsetof(struct lguest_dma, used_len);
|
|
lgwrite_other(dstlg, used_lenp, &ret, sizeof(ret));
|
|
/* Move the cursor for next time. */
|
|
dst->next_dma++;
|
|
}
|
|
up_read(&dstlg->mm->mmap_sem);
|
|
|
|
/* We trigger the destination interrupt, even if the destination was
|
|
* empty and we didn't transfer anything: this gives them a chance to
|
|
* wake up and refill. */
|
|
set_bit(dst->interrupt, dstlg->irqs_pending);
|
|
/* Wake up the destination process. */
|
|
wake_up_process(dstlg->tsk);
|
|
/* If we passed the last "struct lguest_dma", the receive had no
|
|
* buffers left. */
|
|
return i == dst->num_dmas;
|
|
|
|
fail:
|
|
up_read(&dstlg->mm->mmap_sem);
|
|
return 0;
|
|
}
|
|
|
|
/*L:370 This is the counter-side to the BIND_DMA hypercall; the SEND_DMA
|
|
* hypercall. We find out who's listening, and send to them. */
|
|
void send_dma(struct lguest *lg, unsigned long ukey, unsigned long udma)
|
|
{
|
|
union futex_key key;
|
|
int empty = 0;
|
|
struct rw_semaphore *fshared = ¤t->mm->mmap_sem;
|
|
|
|
again:
|
|
mutex_lock(&lguest_lock);
|
|
down_read(fshared);
|
|
/* Get the futex key for the key the Guest gave us */
|
|
if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) {
|
|
kill_guest(lg, "bad sending DMA key");
|
|
goto unlock;
|
|
}
|
|
/* Since the key must be a multiple of 4, the futex key uses the lower
|
|
* bit of the "offset" field (which would always be 0) to indicate a
|
|
* mapping which is shared with other processes (ie. Guests). */
|
|
if (key.shared.offset & 1) {
|
|
struct lguest_dma_info *i;
|
|
/* Look through the hash for other Guests. */
|
|
list_for_each_entry(i, &dma_hash[hash(&key)], list) {
|
|
/* Don't send to ourselves. */
|
|
if (i->guestid == lg->guestid)
|
|
continue;
|
|
if (!key_eq(&key, &i->key))
|
|
continue;
|
|
|
|
/* If dma_transfer() tells us the destination has no
|
|
* available buffers, we increment "empty". */
|
|
empty += dma_transfer(lg, udma, i);
|
|
break;
|
|
}
|
|
/* If the destination is empty, we release our locks and
|
|
* give the destination Guest a brief chance to restock. */
|
|
if (empty == 1) {
|
|
/* Give any recipients one chance to restock. */
|
|
up_read(¤t->mm->mmap_sem);
|
|
mutex_unlock(&lguest_lock);
|
|
/* Next time, we won't try again. */
|
|
empty++;
|
|
goto again;
|
|
}
|
|
} else {
|
|
/* Private mapping: Guest is sending to its Launcher. We set
|
|
* the "dma_is_pending" flag so that the main loop will exit
|
|
* and the Launcher's read() from /dev/lguest will return. */
|
|
lg->dma_is_pending = 1;
|
|
lg->pending_dma = udma;
|
|
lg->pending_key = ukey;
|
|
}
|
|
unlock:
|
|
up_read(fshared);
|
|
mutex_unlock(&lguest_lock);
|
|
}
|
|
/*:*/
|
|
|
|
void release_all_dma(struct lguest *lg)
|
|
{
|
|
unsigned int i;
|
|
|
|
BUG_ON(!mutex_is_locked(&lguest_lock));
|
|
|
|
down_read(&lg->mm->mmap_sem);
|
|
for (i = 0; i < LGUEST_MAX_DMA; i++) {
|
|
if (lg->dma[i].interrupt)
|
|
unlink_dma(&lg->dma[i]);
|
|
}
|
|
up_read(&lg->mm->mmap_sem);
|
|
}
|
|
|
|
/*M:007 We only return a single DMA buffer to the Launcher, but it would be
|
|
* more efficient to return a pointer to the entire array of DMA buffers, which
|
|
* it can cache and choose one whenever it wants.
|
|
*
|
|
* Currently the Launcher uses a write to /dev/lguest, and the return value is
|
|
* the address of the DMA structure with the interrupt number placed in
|
|
* dma->used_len. If we wanted to return the entire array, we need to return
|
|
* the address, array size and interrupt number: this seems to require an
|
|
* ioctl(). :*/
|
|
|
|
/*L:320 This routine looks for a DMA buffer registered by the Guest on the
|
|
* given key (using the BIND_DMA hypercall). */
|
|
unsigned long get_dma_buffer(struct lguest *lg,
|
|
unsigned long ukey, unsigned long *interrupt)
|
|
{
|
|
unsigned long ret = 0;
|
|
union futex_key key;
|
|
struct lguest_dma_info *i;
|
|
struct rw_semaphore *fshared = ¤t->mm->mmap_sem;
|
|
|
|
/* Take the Big Lguest Lock to stop other Guests sending this Guest DMA
|
|
* at the same time. */
|
|
mutex_lock(&lguest_lock);
|
|
/* To match between Guests sharing the same underlying memory we steal
|
|
* code from the futex infrastructure. This requires that we hold the
|
|
* "mmap_sem" for our process (the Launcher), and pass it to the futex
|
|
* code. */
|
|
down_read(fshared);
|
|
|
|
/* This can fail if it's not a valid address, or if the address is not
|
|
* divisible by 4 (the futex code needs that, we don't really). */
|
|
if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) {
|
|
kill_guest(lg, "bad registered DMA buffer");
|
|
goto unlock;
|
|
}
|
|
/* Search the hash table for matching entries (the Launcher can only
|
|
* send to its own Guest for the moment, so the entry must be for this
|
|
* Guest) */
|
|
list_for_each_entry(i, &dma_hash[hash(&key)], list) {
|
|
if (key_eq(&key, &i->key) && i->guestid == lg->guestid) {
|
|
unsigned int j;
|
|
/* Look through the registered DMA array for an
|
|
* available buffer. */
|
|
for (j = 0; j < i->num_dmas; j++) {
|
|
struct lguest_dma dma;
|
|
|
|
ret = i->dmas + j * sizeof(struct lguest_dma);
|
|
lgread(lg, &dma, ret, sizeof(dma));
|
|
if (dma.used_len == 0)
|
|
break;
|
|
}
|
|
/* Store the interrupt the Guest wants when the buffer
|
|
* is used. */
|
|
*interrupt = i->interrupt;
|
|
break;
|
|
}
|
|
}
|
|
unlock:
|
|
up_read(fshared);
|
|
mutex_unlock(&lguest_lock);
|
|
return ret;
|
|
}
|
|
/*:*/
|
|
|
|
/*L:410 This really has completed the Launcher. Not only have we now finished
|
|
* the longest chapter in our journey, but this also means we are over halfway
|
|
* through!
|
|
*
|
|
* Enough prevaricating around the bush: it is time for us to dive into the
|
|
* core of the Host, in "make Host".
|
|
*/
|