x86 mmiotrace: fix save/restore page table state
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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@ -32,6 +32,8 @@ struct kmmio_fault_page {
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struct list_head list;
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struct kmmio_fault_page *release_next;
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unsigned long page; /* location of the fault page */
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bool old_presence; /* page presence prior to arming */
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bool armed;
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/*
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* Number of times this page has been registered as a part
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@ -105,8 +107,7 @@ static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
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return NULL;
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}
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static int set_page_present(unsigned long addr, bool present,
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unsigned int *pglevel)
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static int set_page_presence(unsigned long addr, bool present, bool *old)
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{
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pteval_t pteval;
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pmdval_t pmdval;
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@ -119,20 +120,21 @@ static int set_page_present(unsigned long addr, bool present,
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return -1;
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}
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if (pglevel)
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*pglevel = level;
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switch (level) {
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case PG_LEVEL_2M:
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pmd = (pmd_t *)pte;
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pmdval = pmd_val(*pmd) & ~_PAGE_PRESENT;
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pmdval = pmd_val(*pmd);
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*old = !!(pmdval & _PAGE_PRESENT);
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pmdval &= ~_PAGE_PRESENT;
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if (present)
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pmdval |= _PAGE_PRESENT;
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set_pmd(pmd, __pmd(pmdval));
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break;
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case PG_LEVEL_4K:
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pteval = pte_val(*pte) & ~_PAGE_PRESENT;
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pteval = pte_val(*pte);
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*old = !!(pteval & _PAGE_PRESENT);
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pteval &= ~_PAGE_PRESENT;
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if (present)
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pteval |= _PAGE_PRESENT;
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set_pte_atomic(pte, __pte(pteval));
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@ -148,19 +150,39 @@ static int set_page_present(unsigned long addr, bool present,
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return 0;
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}
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/** Mark the given page as not present. Access to it will trigger a fault. */
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static int arm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
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/*
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* Mark the given page as not present. Access to it will trigger a fault.
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*
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* Struct kmmio_fault_page is protected by RCU and kmmio_lock, but the
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* protection is ignored here. RCU read lock is assumed held, so the struct
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* will not disappear unexpectedly. Furthermore, the caller must guarantee,
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* that double arming the same virtual address (page) cannot occur.
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*
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* Double disarming on the other hand is allowed, and may occur when a fault
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* and mmiotrace shutdown happen simultaneously.
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*/
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static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
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{
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int ret = set_page_present(page & PAGE_MASK, false, pglevel);
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WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", page);
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int ret;
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WARN_ONCE(f->armed, KERN_ERR "kmmio page already armed.\n");
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if (f->armed) {
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pr_warning("kmmio double-arm: page 0x%08lx, ref %d, old %d\n",
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f->page, f->count, f->old_presence);
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}
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ret = set_page_presence(f->page, false, &f->old_presence);
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WARN_ONCE(ret < 0, KERN_ERR "kmmio arming 0x%08lx failed.\n", f->page);
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f->armed = true;
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return ret;
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}
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/** Mark the given page as present. */
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static void disarm_kmmio_fault_page(unsigned long page, unsigned int *pglevel)
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/** Restore the given page to saved presence state. */
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static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
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{
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int ret = set_page_present(page & PAGE_MASK, true, pglevel);
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WARN_ONCE(ret < 0, KERN_ERR "kmmio disarming 0x%08lx failed.\n", page);
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bool tmp;
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int ret = set_page_presence(f->page, f->old_presence, &tmp);
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WARN_ONCE(ret < 0,
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KERN_ERR "kmmio disarming 0x%08lx failed.\n", f->page);
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f->armed = false;
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}
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/*
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@ -207,7 +229,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
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ctx = &get_cpu_var(kmmio_ctx);
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if (ctx->active) {
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disarm_kmmio_fault_page(faultpage->page, NULL);
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disarm_kmmio_fault_page(faultpage);
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if (addr == ctx->addr) {
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/*
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* On SMP we sometimes get recursive probe hits on the
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@ -249,7 +271,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
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regs->flags &= ~X86_EFLAGS_IF;
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/* Now we set present bit in PTE and single step. */
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disarm_kmmio_fault_page(ctx->fpage->page, NULL);
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disarm_kmmio_fault_page(ctx->fpage);
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/*
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* If another cpu accesses the same page while we are stepping,
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@ -288,7 +310,7 @@ static int post_kmmio_handler(unsigned long condition, struct pt_regs *regs)
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if (ctx->probe && ctx->probe->post_handler)
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ctx->probe->post_handler(ctx->probe, condition, regs);
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arm_kmmio_fault_page(ctx->fpage->page, NULL);
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arm_kmmio_fault_page(ctx->fpage);
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regs->flags &= ~X86_EFLAGS_TF;
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regs->flags |= ctx->saved_flags;
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@ -320,19 +342,19 @@ static int add_kmmio_fault_page(unsigned long page)
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f = get_kmmio_fault_page(page);
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if (f) {
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if (!f->count)
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arm_kmmio_fault_page(f->page, NULL);
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arm_kmmio_fault_page(f);
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f->count++;
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return 0;
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}
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f = kmalloc(sizeof(*f), GFP_ATOMIC);
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f = kzalloc(sizeof(*f), GFP_ATOMIC);
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if (!f)
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return -1;
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f->count = 1;
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f->page = page;
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if (arm_kmmio_fault_page(f->page, NULL)) {
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if (arm_kmmio_fault_page(f)) {
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kfree(f);
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return -1;
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}
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@ -356,7 +378,7 @@ static void release_kmmio_fault_page(unsigned long page,
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f->count--;
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BUG_ON(f->count < 0);
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if (!f->count) {
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disarm_kmmio_fault_page(f->page, NULL);
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disarm_kmmio_fault_page(f);
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f->release_next = *release_list;
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*release_list = f;
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}
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