xen: lock pte pages while pinning/unpinning
When a pagetable is created, it is made globally visible in the rmap prio tree before it is pinned via arch_dup_mmap(), and remains in the rmap tree while it is unpinned with arch_exit_mmap(). This means that other CPUs may race with the pinning/unpinning process, and see a pte between when it gets marked RO and actually pinned, causing any pte updates to fail with write-protect faults. As a result, all pte pages must be properly locked, and only unlocked once the pinning/unpinning process has finished. In order to avoid taking spinlocks for the whole pagetable - which may overflow the PREEMPT_BITS portion of preempt counter - it locks and pins each pte page individually, and then finally pins the whole pagetable. Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com> Cc: Rik van Riel <riel@redhat.com> Cc: Hugh Dickens <hugh@veritas.com> Cc: David Rientjes <rientjes@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andi Kleen <ak@suse.de> Cc: Keir Fraser <keir@xensource.com> Cc: Jan Beulich <jbeulich@novell.com>
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@ -666,6 +666,15 @@ static __init void xen_alloc_pt_init(struct mm_struct *mm, u32 pfn)
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make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
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}
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static void pin_pagetable_pfn(unsigned level, unsigned long pfn)
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{
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struct mmuext_op op;
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op.cmd = level;
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op.arg1.mfn = pfn_to_mfn(pfn);
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if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
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BUG();
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}
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/* This needs to make sure the new pte page is pinned iff its being
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attached to a pinned pagetable. */
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static void xen_alloc_pt(struct mm_struct *mm, u32 pfn)
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@ -675,9 +684,10 @@ static void xen_alloc_pt(struct mm_struct *mm, u32 pfn)
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if (PagePinned(virt_to_page(mm->pgd))) {
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SetPagePinned(page);
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if (!PageHighMem(page))
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if (!PageHighMem(page)) {
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make_lowmem_page_readonly(__va(PFN_PHYS(pfn)));
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else
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pin_pagetable_pfn(MMUEXT_PIN_L1_TABLE, pfn);
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} else
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/* make sure there are no stray mappings of
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this page */
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kmap_flush_unused();
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@ -690,10 +700,12 @@ static void xen_release_pt(u32 pfn)
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struct page *page = pfn_to_page(pfn);
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if (PagePinned(page)) {
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if (!PageHighMem(page))
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if (!PageHighMem(page)) {
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pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, pfn);
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make_lowmem_page_readwrite(__va(PFN_PHYS(pfn)));
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}
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}
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}
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#ifdef CONFIG_HIGHPTE
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static void *xen_kmap_atomic_pte(struct page *page, enum km_type type)
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@ -806,15 +818,15 @@ static __init void xen_pagetable_setup_done(pgd_t *base)
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/* Actually pin the pagetable down, but we can't set PG_pinned
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yet because the page structures don't exist yet. */
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{
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struct mmuext_op op;
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unsigned level;
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#ifdef CONFIG_X86_PAE
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op.cmd = MMUEXT_PIN_L3_TABLE;
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level = MMUEXT_PIN_L3_TABLE;
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#else
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op.cmd = MMUEXT_PIN_L3_TABLE;
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level = MMUEXT_PIN_L2_TABLE;
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#endif
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op.arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(base)));
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if (HYPERVISOR_mmuext_op(&op, 1, NULL, DOMID_SELF))
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BUG();
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pin_pagetable_pfn(level, PFN_DOWN(__pa(base)));
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}
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}
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@ -303,7 +303,12 @@ pgd_t xen_make_pgd(unsigned long pgd)
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}
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#endif /* CONFIG_X86_PAE */
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enum pt_level {
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PT_PGD,
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PT_PUD,
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PT_PMD,
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PT_PTE
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};
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/*
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(Yet another) pagetable walker. This one is intended for pinning a
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@ -315,7 +320,7 @@ pgd_t xen_make_pgd(unsigned long pgd)
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FIXADDR_TOP. But the important bit is that we don't pin beyond
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there, because then we start getting into Xen's ptes.
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*/
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static int pgd_walk(pgd_t *pgd_base, int (*func)(struct page *, unsigned),
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static int pgd_walk(pgd_t *pgd_base, int (*func)(struct page *, enum pt_level),
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unsigned long limit)
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{
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pgd_t *pgd = pgd_base;
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@ -340,7 +345,7 @@ static int pgd_walk(pgd_t *pgd_base, int (*func)(struct page *, unsigned),
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pud = pud_offset(pgd, 0);
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if (PTRS_PER_PUD > 1) /* not folded */
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flush |= (*func)(virt_to_page(pud), 0);
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flush |= (*func)(virt_to_page(pud), PT_PUD);
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for (; addr != pud_limit; pud++, addr = pud_next) {
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pmd_t *pmd;
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@ -359,7 +364,7 @@ static int pgd_walk(pgd_t *pgd_base, int (*func)(struct page *, unsigned),
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pmd = pmd_offset(pud, 0);
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if (PTRS_PER_PMD > 1) /* not folded */
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flush |= (*func)(virt_to_page(pmd), 0);
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flush |= (*func)(virt_to_page(pmd), PT_PMD);
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for (; addr != pmd_limit; pmd++) {
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addr += (PAGE_SIZE * PTRS_PER_PTE);
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@ -371,17 +376,47 @@ static int pgd_walk(pgd_t *pgd_base, int (*func)(struct page *, unsigned),
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if (pmd_none(*pmd))
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continue;
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flush |= (*func)(pmd_page(*pmd), 0);
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flush |= (*func)(pmd_page(*pmd), PT_PTE);
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}
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}
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}
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flush |= (*func)(virt_to_page(pgd_base), UVMF_TLB_FLUSH);
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flush |= (*func)(virt_to_page(pgd_base), PT_PGD);
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return flush;
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}
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static int pin_page(struct page *page, unsigned flags)
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static spinlock_t *lock_pte(struct page *page)
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{
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spinlock_t *ptl = NULL;
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#if NR_CPUS >= CONFIG_SPLIT_PTLOCK_CPUS
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ptl = __pte_lockptr(page);
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spin_lock(ptl);
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#endif
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return ptl;
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}
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static void do_unlock(void *v)
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{
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spinlock_t *ptl = v;
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spin_unlock(ptl);
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}
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static void xen_do_pin(unsigned level, unsigned long pfn)
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{
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struct mmuext_op *op;
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struct multicall_space mcs;
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mcs = __xen_mc_entry(sizeof(*op));
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op = mcs.args;
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op->cmd = level;
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op->arg1.mfn = pfn_to_mfn(pfn);
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MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
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}
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static int pin_page(struct page *page, enum pt_level level)
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{
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unsigned pgfl = test_and_set_bit(PG_pinned, &page->flags);
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int flush;
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@ -396,12 +431,26 @@ static int pin_page(struct page *page, unsigned flags)
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void *pt = lowmem_page_address(page);
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unsigned long pfn = page_to_pfn(page);
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struct multicall_space mcs = __xen_mc_entry(0);
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spinlock_t *ptl;
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flush = 0;
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ptl = NULL;
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if (level == PT_PTE)
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ptl = lock_pte(page);
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MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
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pfn_pte(pfn, PAGE_KERNEL_RO),
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flags);
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level == PT_PGD ? UVMF_TLB_FLUSH : 0);
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if (level == PT_PTE)
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xen_do_pin(MMUEXT_PIN_L1_TABLE, pfn);
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if (ptl) {
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/* Queue a deferred unlock for when this batch
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is completed. */
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xen_mc_callback(do_unlock, ptl);
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}
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}
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return flush;
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@ -412,8 +461,7 @@ static int pin_page(struct page *page, unsigned flags)
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read-only, and can be pinned. */
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void xen_pgd_pin(pgd_t *pgd)
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{
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struct multicall_space mcs;
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struct mmuext_op *op;
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unsigned level;
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xen_mc_batch();
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@ -424,16 +472,13 @@ void xen_pgd_pin(pgd_t *pgd)
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xen_mc_batch();
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}
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mcs = __xen_mc_entry(sizeof(*op));
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op = mcs.args;
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#ifdef CONFIG_X86_PAE
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op->cmd = MMUEXT_PIN_L3_TABLE;
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level = MMUEXT_PIN_L3_TABLE;
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#else
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op->cmd = MMUEXT_PIN_L2_TABLE;
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level = MMUEXT_PIN_L2_TABLE;
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#endif
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op->arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(pgd)));
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MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
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xen_do_pin(level, PFN_DOWN(__pa(pgd)));
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xen_mc_issue(0);
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}
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@ -441,7 +486,7 @@ void xen_pgd_pin(pgd_t *pgd)
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/* The init_mm pagetable is really pinned as soon as its created, but
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that's before we have page structures to store the bits. So do all
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the book-keeping now. */
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static __init int mark_pinned(struct page *page, unsigned flags)
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static __init int mark_pinned(struct page *page, enum pt_level level)
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{
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SetPagePinned(page);
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return 0;
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@ -452,18 +497,32 @@ void __init xen_mark_init_mm_pinned(void)
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pgd_walk(init_mm.pgd, mark_pinned, FIXADDR_TOP);
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}
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static int unpin_page(struct page *page, unsigned flags)
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static int unpin_page(struct page *page, enum pt_level level)
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{
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unsigned pgfl = test_and_clear_bit(PG_pinned, &page->flags);
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if (pgfl && !PageHighMem(page)) {
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void *pt = lowmem_page_address(page);
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unsigned long pfn = page_to_pfn(page);
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struct multicall_space mcs = __xen_mc_entry(0);
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spinlock_t *ptl = NULL;
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struct multicall_space mcs;
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if (level == PT_PTE) {
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ptl = lock_pte(page);
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xen_do_pin(MMUEXT_UNPIN_TABLE, pfn);
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}
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mcs = __xen_mc_entry(0);
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MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
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pfn_pte(pfn, PAGE_KERNEL),
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flags);
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level == PT_PGD ? UVMF_TLB_FLUSH : 0);
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if (ptl) {
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/* unlock when batch completed */
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xen_mc_callback(do_unlock, ptl);
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}
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}
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return 0; /* never need to flush on unpin */
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@ -472,18 +531,9 @@ static int unpin_page(struct page *page, unsigned flags)
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/* Release a pagetables pages back as normal RW */
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static void xen_pgd_unpin(pgd_t *pgd)
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{
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struct mmuext_op *op;
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struct multicall_space mcs;
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xen_mc_batch();
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mcs = __xen_mc_entry(sizeof(*op));
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op = mcs.args;
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op->cmd = MMUEXT_UNPIN_TABLE;
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op->arg1.mfn = pfn_to_mfn(PFN_DOWN(__pa(pgd)));
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MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
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xen_do_pin(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));
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pgd_walk(pgd, unpin_page, TASK_SIZE);
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@ -585,5 +635,6 @@ void xen_exit_mmap(struct mm_struct *mm)
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/* pgd may not be pinned in the error exit path of execve */
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if (PagePinned(virt_to_page(mm->pgd)))
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xen_pgd_unpin(mm->pgd);
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spin_unlock(&mm->page_table_lock);
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}
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@ -137,7 +137,6 @@ config SPLIT_PTLOCK_CPUS
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int
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default "4096" if ARM && !CPU_CACHE_VIPT
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default "4096" if PARISC && !PA20
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default "4096" if XEN
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default "4"
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#
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