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alistair23-linux/arch/s390/mm/fault.c
Martin Schwidefsky b6d09449d5 [PATCH] s390: pfault interrupt race 
There is a race in pfault_interrupt.  That function gets called two times for
each pfault notification.  Once with a subcode of 0 to indicate that a real
page is not available and once with a subcode of 0x80 to indicate that the
page is present again.

Since the two external interrupts can be delivered on two different cpus the
order in which the two calls are made is unpredictable.  It is possible that
the subcode 0x80 interrupt is completed before the subcode 0x00 interrupt has
done the wake_up() call.

To avoid calling wake_up() on an already removed task structure proper task
structure reference counting is needed.  Increase the reference counter in the
subcode 0x00 interrupt before setting pfault_wait to zero and return the
reference after the wake_up call.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-09-05 00:06:28 -07:00

590 lines
17 KiB
C
Raw Blame History

/*
* arch/s390/mm/fault.c
*
* S390 version
* Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
* Author(s): Hartmut Penner (hp@de.ibm.com)
* Ulrich Weigand (uweigand@de.ibm.com)
*
* Derived from "arch/i386/mm/fault.c"
* Copyright (C) 1995 Linus Torvalds
*/
#include <linux/config.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/console.h>
#include <linux/module.h>
#include <linux/hardirq.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#ifndef CONFIG_ARCH_S390X
#define __FAIL_ADDR_MASK 0x7ffff000
#define __FIXUP_MASK 0x7fffffff
#define __SUBCODE_MASK 0x0200
#define __PF_RES_FIELD 0ULL
#else /* CONFIG_ARCH_S390X */
#define __FAIL_ADDR_MASK -4096L
#define __FIXUP_MASK ~0L
#define __SUBCODE_MASK 0x0600
#define __PF_RES_FIELD 0x8000000000000000ULL
#endif /* CONFIG_ARCH_S390X */
#ifdef CONFIG_SYSCTL
extern int sysctl_userprocess_debug;
#endif
extern void die(const char *,struct pt_regs *,long);
extern spinlock_t timerlist_lock;
/*
* Unlock any spinlocks which will prevent us from getting the
* message out (timerlist_lock is acquired through the
* console unblank code)
*/
void bust_spinlocks(int yes)
{
if (yes) {
oops_in_progress = 1;
} else {
int loglevel_save = console_loglevel;
console_unblank();
oops_in_progress = 0;
/*
* OK, the message is on the console. Now we call printk()
* without oops_in_progress set so that printk will give klogd
* a poke. Hold onto your hats...
*/
console_loglevel = 15;
printk(" ");
console_loglevel = loglevel_save;
}
}
/*
* Check which address space is addressed by the access
* register in S390_lowcore.exc_access_id.
* Returns 1 for user space and 0 for kernel space.
*/
static int __check_access_register(struct pt_regs *regs, int error_code)
{
int areg = S390_lowcore.exc_access_id;
if (areg == 0)
/* Access via access register 0 -> kernel address */
return 0;
save_access_regs(current->thread.acrs);
if (regs && areg < NUM_ACRS && current->thread.acrs[areg] <= 1)
/*
* access register contains 0 -> kernel address,
* access register contains 1 -> user space address
*/
return current->thread.acrs[areg];
/* Something unhealthy was done with the access registers... */
die("page fault via unknown access register", regs, error_code);
do_exit(SIGKILL);
return 0;
}
/*
* Check which address space the address belongs to.
* Returns 1 for user space and 0 for kernel space.
*/
static inline int check_user_space(struct pt_regs *regs, int error_code)
{
/*
* The lowest two bits of S390_lowcore.trans_exc_code indicate
* which paging table was used:
* 0: Primary Segment Table Descriptor
* 1: STD determined via access register
* 2: Secondary Segment Table Descriptor
* 3: Home Segment Table Descriptor
*/
int descriptor = S390_lowcore.trans_exc_code & 3;
if (unlikely(descriptor == 1))
return __check_access_register(regs, error_code);
if (descriptor == 2)
return current->thread.mm_segment.ar4;
return descriptor != 0;
}
/*
* Send SIGSEGV to task. This is an external routine
* to keep the stack usage of do_page_fault small.
*/
static void do_sigsegv(struct pt_regs *regs, unsigned long error_code,
int si_code, unsigned long address)
{
struct siginfo si;
#if defined(CONFIG_SYSCTL) || defined(CONFIG_PROCESS_DEBUG)
#if defined(CONFIG_SYSCTL)
if (sysctl_userprocess_debug)
#endif
{
printk("User process fault: interruption code 0x%lX\n",
error_code);
printk("failing address: %lX\n", address);
show_regs(regs);
}
#endif
si.si_signo = SIGSEGV;
si.si_code = si_code;
si.si_addr = (void *) address;
force_sig_info(SIGSEGV, &si, current);
}
/*
* This routine handles page faults. It determines the address,
* and the problem, and then passes it off to one of the appropriate
* routines.
*
* error_code:
* 04 Protection -> Write-Protection (suprression)
* 10 Segment translation -> Not present (nullification)
* 11 Page translation -> Not present (nullification)
* 3b Region third trans. -> Not present (nullification)
*/
extern inline void
do_exception(struct pt_regs *regs, unsigned long error_code, int is_protection)
{
struct task_struct *tsk;
struct mm_struct *mm;
struct vm_area_struct * vma;
unsigned long address;
int user_address;
const struct exception_table_entry *fixup;
int si_code = SEGV_MAPERR;
tsk = current;
mm = tsk->mm;
/*
* Check for low-address protection. This needs to be treated
* as a special case because the translation exception code
* field is not guaranteed to contain valid data in this case.
*/
if (is_protection && !(S390_lowcore.trans_exc_code & 4)) {
/* Low-address protection hit in kernel mode means
NULL pointer write access in kernel mode. */
if (!(regs->psw.mask & PSW_MASK_PSTATE)) {
address = 0;
user_address = 0;
goto no_context;
}
/* Low-address protection hit in user mode 'cannot happen'. */
die ("Low-address protection", regs, error_code);
do_exit(SIGKILL);
}
/*
* get the failing address
* more specific the segment and page table portion of
* the address
*/
address = S390_lowcore.trans_exc_code & __FAIL_ADDR_MASK;
user_address = check_user_space(regs, error_code);
/*
* Verify that the fault happened in user space, that
* we are not in an interrupt and that there is a
* user context.
*/
if (user_address == 0 || in_atomic() || !mm)
goto no_context;
/*
* When we get here, the fault happened in the current
* task's user address space, so we can switch on the
* interrupts again and then search the VMAs
*/
local_irq_enable();
down_read(&mm->mmap_sem);
vma = find_vma(mm, address);
if (!vma)
goto bad_area;
if (vma->vm_start <= address)
goto good_area;
if (!(vma->vm_flags & VM_GROWSDOWN))
goto bad_area;
if (expand_stack(vma, address))
goto bad_area;
/*
* Ok, we have a good vm_area for this memory access, so
* we can handle it..
*/
good_area:
si_code = SEGV_ACCERR;
if (!is_protection) {
/* page not present, check vm flags */
if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
goto bad_area;
} else {
if (!(vma->vm_flags & VM_WRITE))
goto bad_area;
}
survive:
/*
* If for any reason at all we couldn't handle the fault,
* make sure we exit gracefully rather than endlessly redo
* the fault.
*/
switch (handle_mm_fault(mm, vma, address, is_protection)) {
case VM_FAULT_MINOR:
tsk->min_flt++;
break;
case VM_FAULT_MAJOR:
tsk->maj_flt++;
break;
case VM_FAULT_SIGBUS:
goto do_sigbus;
case VM_FAULT_OOM:
goto out_of_memory;
default:
BUG();
}
up_read(&mm->mmap_sem);
/*
* The instruction that caused the program check will
* be repeated. Don't signal single step via SIGTRAP.
*/
clear_tsk_thread_flag(current, TIF_SINGLE_STEP);
return;
/*
* Something tried to access memory that isn't in our memory map..
* Fix it, but check if it's kernel or user first..
*/
bad_area:
up_read(&mm->mmap_sem);
/* User mode accesses just cause a SIGSEGV */
if (regs->psw.mask & PSW_MASK_PSTATE) {
tsk->thread.prot_addr = address;
tsk->thread.trap_no = error_code;
do_sigsegv(regs, error_code, si_code, address);
return;
}
no_context:
/* Are we prepared to handle this kernel fault? */
fixup = search_exception_tables(regs->psw.addr & __FIXUP_MASK);
if (fixup) {
regs->psw.addr = fixup->fixup | PSW_ADDR_AMODE;
return;
}
/*
* Oops. The kernel tried to access some bad page. We'll have to
* terminate things with extreme prejudice.
*/
if (user_address == 0)
printk(KERN_ALERT "Unable to handle kernel pointer dereference"
" at virtual kernel address %p\n", (void *)address);
else
printk(KERN_ALERT "Unable to handle kernel paging request"
" at virtual user address %p\n", (void *)address);
die("Oops", regs, error_code);
do_exit(SIGKILL);
/*
* We ran out of memory, or some other thing happened to us that made
* us unable to handle the page fault gracefully.
*/
out_of_memory:
up_read(&mm->mmap_sem);
if (tsk->pid == 1) {
yield();
goto survive;
}
printk("VM: killing process %s\n", tsk->comm);
if (regs->psw.mask & PSW_MASK_PSTATE)
do_exit(SIGKILL);
goto no_context;
do_sigbus:
up_read(&mm->mmap_sem);
/*
* Send a sigbus, regardless of whether we were in kernel
* or user mode.
*/
tsk->thread.prot_addr = address;
tsk->thread.trap_no = error_code;
force_sig(SIGBUS, tsk);
/* Kernel mode? Handle exceptions or die */
if (!(regs->psw.mask & PSW_MASK_PSTATE))
goto no_context;
}
void do_protection_exception(struct pt_regs *regs, unsigned long error_code)
{
regs->psw.addr -= (error_code >> 16);
do_exception(regs, 4, 1);
}
void do_dat_exception(struct pt_regs *regs, unsigned long error_code)
{
do_exception(regs, error_code & 0xff, 0);
}
#ifndef CONFIG_ARCH_S390X
typedef struct _pseudo_wait_t {
struct _pseudo_wait_t *next;
wait_queue_head_t queue;
unsigned long address;
int resolved;
} pseudo_wait_t;
static pseudo_wait_t *pseudo_lock_queue = NULL;
static spinlock_t pseudo_wait_spinlock; /* spinlock to protect lock queue */
/*
* This routine handles 'pagex' pseudo page faults.
*/
asmlinkage void
do_pseudo_page_fault(struct pt_regs *regs, unsigned long error_code)
{
pseudo_wait_t wait_struct;
pseudo_wait_t *ptr, *last, *next;
unsigned long address;
/*
* get the failing address
* more specific the segment and page table portion of
* the address
*/
address = S390_lowcore.trans_exc_code & 0xfffff000;
if (address & 0x80000000) {
/* high bit set -> a page has been swapped in by VM */
address &= 0x7fffffff;
spin_lock(&pseudo_wait_spinlock);
last = NULL;
ptr = pseudo_lock_queue;
while (ptr != NULL) {
next = ptr->next;
if (address == ptr->address) {
/*
* This is one of the processes waiting
* for the page. Unchain from the queue.
* There can be more than one process
* waiting for the same page. VM presents
* an initial and a completion interrupt for
* every process that tries to access a
* page swapped out by VM.
*/
if (last == NULL)
pseudo_lock_queue = next;
else
last->next = next;
/* now wake up the process */
ptr->resolved = 1;
wake_up(&ptr->queue);
} else
last = ptr;
ptr = next;
}
spin_unlock(&pseudo_wait_spinlock);
} else {
/* Pseudo page faults in kernel mode is a bad idea */
if (!(regs->psw.mask & PSW_MASK_PSTATE)) {
/*
* VM presents pseudo page faults if the interrupted
* state was not disabled for interrupts. So we can
* get pseudo page fault interrupts while running
* in kernel mode. We simply access the page here
* while we are running disabled. VM will then swap
* in the page synchronously.
*/
if (check_user_space(regs, error_code) == 0)
/* dereference a virtual kernel address */
__asm__ __volatile__ (
" ic 0,0(%0)"
: : "a" (address) : "0");
else
/* dereference a virtual user address */
__asm__ __volatile__ (
" la 2,0(%0)\n"
" sacf 512\n"
" ic 2,0(2)\n"
"0:sacf 0\n"
".section __ex_table,\"a\"\n"
" .align 4\n"
" .long 0b,0b\n"
".previous"
: : "a" (address) : "2" );
return;
}
/* initialize and add element to pseudo_lock_queue */
init_waitqueue_head (&wait_struct.queue);
wait_struct.address = address;
wait_struct.resolved = 0;
spin_lock(&pseudo_wait_spinlock);
wait_struct.next = pseudo_lock_queue;
pseudo_lock_queue = &wait_struct;
spin_unlock(&pseudo_wait_spinlock);
/*
* The instruction that caused the program check will
* be repeated. Don't signal single step via SIGTRAP.
*/
clear_tsk_thread_flag(current, TIF_SINGLE_STEP);
/* go to sleep */
wait_event(wait_struct.queue, wait_struct.resolved);
}
}
#endif /* CONFIG_ARCH_S390X */
#ifdef CONFIG_PFAULT
/*
* 'pfault' pseudo page faults routines.
*/
static int pfault_disable = 0;
static int __init nopfault(char *str)
{
pfault_disable = 1;
return 1;
}
__setup("nopfault", nopfault);
typedef struct {
__u16 refdiagc;
__u16 reffcode;
__u16 refdwlen;
__u16 refversn;
__u64 refgaddr;
__u64 refselmk;
__u64 refcmpmk;
__u64 reserved;
} __attribute__ ((packed)) pfault_refbk_t;
int pfault_init(void)
{
pfault_refbk_t refbk =
{ 0x258, 0, 5, 2, __LC_CURRENT, 1ULL << 48, 1ULL << 48,
__PF_RES_FIELD };
int rc;
if (pfault_disable)
return -1;
__asm__ __volatile__(
" diag %1,%0,0x258\n"
"0: j 2f\n"
"1: la %0,8\n"
"2:\n"
".section __ex_table,\"a\"\n"
" .align 4\n"
#ifndef CONFIG_ARCH_S390X
" .long 0b,1b\n"
#else /* CONFIG_ARCH_S390X */
" .quad 0b,1b\n"
#endif /* CONFIG_ARCH_S390X */
".previous"
: "=d" (rc) : "a" (&refbk) : "cc" );
__ctl_set_bit(0, 9);
return rc;
}
void pfault_fini(void)
{
pfault_refbk_t refbk =
{ 0x258, 1, 5, 2, 0ULL, 0ULL, 0ULL, 0ULL };
if (pfault_disable)
return;
__ctl_clear_bit(0,9);
__asm__ __volatile__(
" diag %0,0,0x258\n"
"0:\n"
".section __ex_table,\"a\"\n"
" .align 4\n"
#ifndef CONFIG_ARCH_S390X
" .long 0b,0b\n"
#else /* CONFIG_ARCH_S390X */
" .quad 0b,0b\n"
#endif /* CONFIG_ARCH_S390X */
".previous"
: : "a" (&refbk) : "cc" );
}
asmlinkage void
pfault_interrupt(struct pt_regs *regs, __u16 error_code)
{
struct task_struct *tsk;
__u16 subcode;
/*
* Get the external interruption subcode & pfault
* initial/completion signal bit. VM stores this
* in the 'cpu address' field associated with the
* external interrupt.
*/
subcode = S390_lowcore.cpu_addr;
if ((subcode & 0xff00) != __SUBCODE_MASK)
return;
/*
* Get the token (= address of the task structure of the affected task).
*/
tsk = *(struct task_struct **) __LC_PFAULT_INTPARM;
if (subcode & 0x0080) {
/* signal bit is set -> a page has been swapped in by VM */
if (xchg(&tsk->thread.pfault_wait, -1) != 0) {
/* Initial interrupt was faster than the completion
* interrupt. pfault_wait is valid. Set pfault_wait
* back to zero and wake up the process. This can
* safely be done because the task is still sleeping
* and can't produce new pfaults. */
tsk->thread.pfault_wait = 0;
wake_up_process(tsk);
put_task_struct(tsk);
}
} else {
/* signal bit not set -> a real page is missing. */
get_task_struct(tsk);
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
if (xchg(&tsk->thread.pfault_wait, 1) != 0) {
/* Completion interrupt was faster than the initial
* interrupt (swapped in a -1 for pfault_wait). Set
* pfault_wait back to zero and exit. This can be
* done safely because tsk is running in kernel
* mode and can't produce new pfaults. */
tsk->thread.pfault_wait = 0;
set_task_state(tsk, TASK_RUNNING);
put_task_struct(tsk);
} else
set_tsk_need_resched(tsk);
}
}
#endif
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