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x86 mmiotrace: fix save/restore page table state
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From baa99e2b32449ec7bf147c234adfa444caecac8a Mon Sep 17 00:00:00 2001
From: Pekka Paalanen <pq@iki.fi>
Date: Sun, 22 Feb 2009 20:02:43 +0200

Blindly setting _PAGE_PRESENT in disarm_kmmio_fault_page() overlooks the
possibility, that the page was not present when it was armed.

Make arm_kmmio_fault_page() store the previous page presence in struct
kmmio_fault_page and use it on disarm.

This patch was originally written by Stuart Bennett, but Pekka Paalanen
rewrote it a little different.

Signed-off-by: Pekka Paalanen <pq@iki.fi>
Cc: Stuart Bennett <stuart@freedesktop.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Pekka Paalanen authored and Ingo Molnar committed Mar 2, 2009
1 parent e9d54ca commit 5359b58
Showing 1 changed file with 44 additions and 22 deletions.
66 changes: 44 additions & 22 deletions arch/x86/mm/kmmio.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,8 @@ struct kmmio_fault_page {
struct list_head list;
struct kmmio_fault_page *release_next;
unsigned long page; /* location of the fault page */
bool old_presence; /* page presence prior to arming */
bool armed;

/*
* Number of times this page has been registered as a part
Expand Down Expand Up @@ -105,8 +107,7 @@ static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
return NULL;
}

static int set_page_present(unsigned long addr, bool present,
unsigned int *pglevel)
static int set_page_presence(unsigned long addr, bool present, bool *old)
{
pteval_t pteval;
pmdval_t pmdval;
Expand All @@ -119,20 +120,21 @@ static int set_page_present(unsigned long addr, bool present,
return -1;
}

if (pglevel)
*pglevel = level;

switch (level) {
case PG_LEVEL_2M:
pmd = (pmd_t *)pte;
pmdval = pmd_val(*pmd) & ~_PAGE_PRESENT;
pmdval = pmd_val(*pmd);
*old = !!(pmdval & _PAGE_PRESENT);
pmdval &= ~_PAGE_PRESENT;
if (present)
pmdval |= _PAGE_PRESENT;
set_pmd(pmd, __pmd(pmdval));
break;

case PG_LEVEL_4K:
pteval = pte_val(*pte) & ~_PAGE_PRESENT;
pteval = pte_val(*pte);
*old = !!(pteval & _PAGE_PRESENT);
pteval &= ~_PAGE_PRESENT;
if (present)
pteval |= _PAGE_PRESENT;
set_pte_atomic(pte, __pte(pteval));
Expand All @@ -148,19 +150,39 @@ static int set_page_present(unsigned long addr, bool present,
return 0;
}

/** Mark the given page as not present. Access to it will trigger a fault. */
static int arm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
/*
* Mark the given page as not present. Access to it will trigger a fault.
*
* Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the
* protection is ignored here. RCU read lock is assumed held, so the struct
* will not disappear unexpectedly. Furthermore, the caller must guarantee,
* that double arming the same virtual address (page) cannot occur.
*
* Double disarming on the other hand is allowed, and may occur when a fault
* and mmiotrace shutdown happen simultaneously.
*/
static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
{
int ret = set_page_present(page & PAGE_MASK, false, pglevel);
WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", page);
int ret;
WARN_ONCE(f->armed, KERN_ERR "kmmio page already armed.\n");
if (f->armed) {
pr_warning("kmmio double-arm: page 0x%08lx, ref %d, old %d\n",
f->page, f->count, f->old_presence);
}
ret = set_page_presence(f->page, false, &f->old_presence);
WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", f->page);
f->armed = true;
return ret;
}

/** Mark the given page as present. */
static void disarm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
/** Restore the given page to saved presence state. */
static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
{
int ret = set_page_present(page & PAGE_MASK, true, pglevel);
WARN_ONCE(ret < 0, KERN_ERR "kmmio disarming 0x%08lx failed.\n", page);
bool tmp;
int ret = set_page_presence(f->page, f->old_presence, &tmp);
WARN_ONCE(ret < 0,
KERN_ERR "kmmio disarming 0x%08lx failed.\n", f->page);
f->armed = false;
}

/*
Expand Down Expand Up @@ -207,7 +229,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)

ctx = &get_cpu_var(kmmio_ctx);
if (ctx->active) {
disarm_kmmio_fault_page(faultpage->page, NULL);
disarm_kmmio_fault_page(faultpage);
if (addr == ctx->addr) {
/*
* On SMP we sometimes get recursive probe hits on the
Expand Down Expand Up @@ -249,7 +271,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
regs->flags &= ~X86_EFLAGS_IF;

/* Now we set present bit in PTE and single step. */
disarm_kmmio_fault_page(ctx->fpage->page, NULL);
disarm_kmmio_fault_page(ctx->fpage);

/*
* If another cpu accesses the same page while we are stepping,
Expand Down Expand Up @@ -288,7 +310,7 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
if (ctx->probe && ctx->probe->post_handler)
ctx->probe->post_handler(ctx->probe, condition, regs);

arm_kmmio_fault_page(ctx->fpage->page, NULL);
arm_kmmio_fault_page(ctx->fpage);

regs->flags &= ~X86_EFLAGS_TF;
regs->flags |= ctx->saved_flags;
Expand Down Expand Up @@ -320,19 +342,19 @@ static int add_kmmio_fault_page(unsigned long page)
f = get_kmmio_fault_page(page);
if (f) {
if (!f->count)
arm_kmmio_fault_page(f->page, NULL);
arm_kmmio_fault_page(f);
f->count++;
return 0;
}

f = kmalloc(sizeof(*f), GFP_ATOMIC);
f = kzalloc(sizeof(*f), GFP_ATOMIC);
if (!f)
return -1;

f->count = 1;
f->page = page;

if (arm_kmmio_fault_page(f->page, NULL)) {
if (arm_kmmio_fault_page(f)) {
kfree(f);
return -1;
}
Expand All @@ -356,7 +378,7 @@ static void release_kmmio_fault_page(unsigned long page,
f->count--;
BUG_ON(f->count < 0);
if (!f->count) {
disarm_kmmio_fault_page(f->page, NULL);
disarm_kmmio_fault_page(f);
f->release_next = *release_list;
*release_list = f;
}
Expand Down

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