From: Aneesh Kumar K.V Date: Mon, 30 Mar 2015 05:11:03 +0000 (+0530) Subject: powerpc/mm/thp: Make page table walk safe against thp split/collapse X-Git-Tag: firefly_0821_release~176^2~1859^2~3 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=691e95fd7396905a38d98919e9c150dbc3ea21a3;p=firefly-linux-kernel-4.4.55.git powerpc/mm/thp: Make page table walk safe against thp split/collapse We can disable a THP split or a hugepage collapse by disabling irq. We do send IPI to all the cpus in the early part of split/collapse, and disabling local irq ensure we don't make progress with split/collapse. If the THP is getting split we return NULL from find_linux_pte_or_hugepte(). For all the current callers it should be ok. We need to be careful if we want to use returned pte_t pointer outside the irq disabled region. W.r.t to THP split, the pfn remains the same, but then a hugepage collapse will result in a pfn change. There are few steps we can take to avoid a hugepage collapse.One way is to take page reference inside the irq disable region. Other option is to take mmap_sem so that a parallel collapse will not happen. We can also disable collapse by taking pmd_lock. Another method used by kvm subsystem is to check whether we had a mmu_notifer update in between using mmu_notifier_retry(). Signed-off-by: Aneesh Kumar K.V Signed-off-by: Michael Ellerman --- diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h index 92fe01c355a9..11a38635dd65 100644 --- a/arch/powerpc/include/asm/pgtable.h +++ b/arch/powerpc/include/asm/pgtable.h @@ -247,8 +247,17 @@ extern int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, #define pmd_large(pmd) 0 #define has_transparent_hugepage() 0 #endif -pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, +pte_t *__find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, unsigned *shift); +static inline pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, + unsigned *shift) +{ + if (!arch_irqs_disabled()) { + pr_info("%s called with irq enabled\n", __func__); + dump_stack(); + } + return __find_linux_pte_or_hugepte(pgdir, ea, shift); +} #endif /* __ASSEMBLY__ */ #endif /* __KERNEL__ */ diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c index a4c62eb0ee48..44b480e3a5af 100644 --- a/arch/powerpc/kernel/eeh.c +++ b/arch/powerpc/kernel/eeh.c @@ -334,9 +334,11 @@ static inline unsigned long eeh_token_to_phys(unsigned long token) int hugepage_shift; /* - * We won't find hugepages here, iomem + * We won't find hugepages here(this is iomem). Hence we are not + * worried about _PAGE_SPLITTING/collapse. Also we will not hit + * page table free, because of init_mm. */ - ptep = find_linux_pte_or_hugepte(init_mm.pgd, token, &hugepage_shift); + ptep = __find_linux_pte_or_hugepte(init_mm.pgd, token, &hugepage_shift); if (!ptep) return token; WARN_ON(hugepage_shift); diff --git a/arch/powerpc/kernel/io-workarounds.c b/arch/powerpc/kernel/io-workarounds.c index 24b968f8e4d8..63d9cc4d7366 100644 --- a/arch/powerpc/kernel/io-workarounds.c +++ b/arch/powerpc/kernel/io-workarounds.c @@ -71,15 +71,15 @@ struct iowa_bus *iowa_mem_find_bus(const PCI_IO_ADDR addr) vaddr = (unsigned long)PCI_FIX_ADDR(addr); if (vaddr < PHB_IO_BASE || vaddr >= PHB_IO_END) return NULL; - - ptep = find_linux_pte_or_hugepte(init_mm.pgd, vaddr, + /* + * We won't find huge pages here (iomem). Also can't hit + * a page table free due to init_mm + */ + ptep = __find_linux_pte_or_hugepte(init_mm.pgd, vaddr, &hugepage_shift); if (ptep == NULL) paddr = 0; else { - /* - * we don't have hugepages backing iomem - */ WARN_ON(hugepage_shift); paddr = pte_pfn(*ptep) << PAGE_SHIFT; } diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c index 534acb3c6c3d..26df3864d85a 100644 --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c @@ -539,12 +539,13 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu, if (!writing && hpte_is_writable(r)) { unsigned int hugepage_shift; pte_t *ptep, pte; + unsigned long flags; /* * We need to protect against page table destruction * while looking up and updating the pte. */ - rcu_read_lock_sched(); + local_irq_save(flags); ptep = find_linux_pte_or_hugepte(current->mm->pgd, hva, &hugepage_shift); if (ptep) { @@ -553,7 +554,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu, if (pte_write(pte)) write_ok = 1; } - rcu_read_unlock_sched(); + local_irq_restore(flags); } } diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c index 73e083cb9f7e..f559b25de173 100644 --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c @@ -26,11 +26,14 @@ static void *real_vmalloc_addr(void *x) { unsigned long addr = (unsigned long) x; pte_t *p; - - p = find_linux_pte_or_hugepte(swapper_pg_dir, addr, NULL); + /* + * assume we don't have huge pages in vmalloc space... + * So don't worry about THP collapse/split. Called + * Only in realmode, hence won't need irq_save/restore. + */ + p = __find_linux_pte_or_hugepte(swapper_pg_dir, addr, NULL); if (!p || !pte_present(*p)) return NULL; - /* assume we don't have huge pages in vmalloc space... */ addr = (pte_pfn(*p) << PAGE_SHIFT) | (addr & ~PAGE_MASK); return __va(addr); } @@ -153,7 +156,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags, pte_t *ptep; unsigned int writing; unsigned long mmu_seq; - unsigned long rcbits; + unsigned long rcbits, irq_flags = 0; psize = hpte_page_size(pteh, ptel); if (!psize) @@ -189,7 +192,16 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags, /* Translate to host virtual address */ hva = __gfn_to_hva_memslot(memslot, gfn); - ptep = find_linux_pte_or_hugepte(pgdir, hva, &hpage_shift); + /* + * If we had a page table table change after lookup, we would + * retry via mmu_notifier_retry. + */ + if (realmode) + ptep = __find_linux_pte_or_hugepte(pgdir, hva, &hpage_shift); + else { + local_irq_save(irq_flags); + ptep = find_linux_pte_or_hugepte(pgdir, hva, &hpage_shift); + } if (ptep) { pte_t pte; unsigned int host_pte_size; @@ -202,9 +214,11 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags, * We should always find the guest page size * to <= host page size, if host is using hugepage */ - if (host_pte_size < psize) + if (host_pte_size < psize) { + if (!realmode) + local_irq_restore(flags); return H_PARAMETER; - + } pte = kvmppc_read_update_linux_pte(ptep, writing, hpage_shift); if (pte_present(pte) && !pte_protnone(pte)) { if (writing && !pte_write(pte)) @@ -216,6 +230,8 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags, pa |= gpa & ~PAGE_MASK; } } + if (!realmode) + local_irq_restore(irq_flags); ptel &= ~(HPTE_R_PP0 - psize); ptel |= pa; diff --git a/arch/powerpc/kvm/e500_mmu_host.c b/arch/powerpc/kvm/e500_mmu_host.c index a1f5b0d4b1d6..4d33e199edcc 100644 --- a/arch/powerpc/kvm/e500_mmu_host.c +++ b/arch/powerpc/kvm/e500_mmu_host.c @@ -338,6 +338,7 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500, pte_t *ptep; unsigned int wimg = 0; pgd_t *pgdir; + unsigned long flags; /* used to check for invalidations in progress */ mmu_seq = kvm->mmu_notifier_seq; @@ -468,14 +469,23 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500, pgdir = vcpu_e500->vcpu.arch.pgdir; + /* + * We are just looking at the wimg bits, so we don't + * care much about the trans splitting bit. + * We are holding kvm->mmu_lock so a notifier invalidate + * can't run hence pfn won't change. + */ + local_irq_save(flags); ptep = find_linux_pte_or_hugepte(pgdir, hva, NULL); if (ptep) { pte_t pte = READ_ONCE(*ptep); - if (pte_present(pte)) + if (pte_present(pte)) { wimg = (pte_val(pte) >> PTE_WIMGE_SHIFT) & MAS2_WIMGE_MASK; - else { + local_irq_restore(flags); + } else { + local_irq_restore(flags); pr_err_ratelimited("%s: pte not present: gfn %lx,pfn %lx\n", __func__, (long)gfn, pfn); ret = -EINVAL; diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c index 2c2022d16059..444f7a5b859b 100644 --- a/arch/powerpc/mm/hash_utils_64.c +++ b/arch/powerpc/mm/hash_utils_64.c @@ -1066,7 +1066,7 @@ int hash_page_mm(struct mm_struct *mm, unsigned long ea, #endif /* CONFIG_PPC_64K_PAGES */ /* Get PTE and page size from page tables */ - ptep = find_linux_pte_or_hugepte(pgdir, ea, &hugeshift); + ptep = __find_linux_pte_or_hugepte(pgdir, ea, &hugeshift); if (ptep == NULL || !pte_present(*ptep)) { DBG_LOW(" no PTE !\n"); rc = 1; diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c index 2cb278a2f658..a9dbb27ca887 100644 --- a/arch/powerpc/mm/hugetlbpage.c +++ b/arch/powerpc/mm/hugetlbpage.c @@ -109,7 +109,7 @@ int pgd_huge(pgd_t pgd) pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr) { /* Only called for hugetlbfs pages, hence can ignore THP */ - return find_linux_pte_or_hugepte(mm->pgd, addr, NULL); + return __find_linux_pte_or_hugepte(mm->pgd, addr, NULL); } static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp, @@ -682,28 +682,35 @@ void hugetlb_free_pgd_range(struct mmu_gather *tlb, } while (addr = next, addr != end); } +/* + * We are holding mmap_sem, so a parallel huge page collapse cannot run. + * To prevent hugepage split, disable irq. + */ struct page * follow_huge_addr(struct mm_struct *mm, unsigned long address, int write) { pte_t *ptep; struct page *page; unsigned shift; - unsigned long mask; + unsigned long mask, flags; /* * Transparent hugepages are handled by generic code. We can skip them * here. */ + local_irq_save(flags); ptep = find_linux_pte_or_hugepte(mm->pgd, address, &shift); /* Verify it is a huge page else bail. */ - if (!ptep || !shift || pmd_trans_huge(*(pmd_t *)ptep)) + if (!ptep || !shift || pmd_trans_huge(*(pmd_t *)ptep)) { + local_irq_restore(flags); return ERR_PTR(-EINVAL); - + } mask = (1UL << shift) - 1; page = pte_page(*ptep); if (page) page += (address & mask) / PAGE_SIZE; + local_irq_restore(flags); return page; } @@ -950,9 +957,12 @@ void flush_dcache_icache_hugepage(struct page *page) * * So long as we atomically load page table pointers we are safe against teardown, * we can follow the address down to the the page and take a ref on it. + * This function need to be called with interrupts disabled. We use this variant + * when we have MSR[EE] = 0 but the paca->soft_enabled = 1 */ -pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, unsigned *shift) +pte_t *__find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea, + unsigned *shift) { pgd_t pgd, *pgdp; pud_t pud, *pudp; @@ -1031,7 +1041,7 @@ out: *shift = pdshift; return ret_pte; } -EXPORT_SYMBOL_GPL(find_linux_pte_or_hugepte); +EXPORT_SYMBOL_GPL(__find_linux_pte_or_hugepte); int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c index ead55351b254..ff09cde20cd2 100644 --- a/arch/powerpc/perf/callchain.c +++ b/arch/powerpc/perf/callchain.c @@ -111,41 +111,45 @@ perf_callchain_kernel(struct perf_callchain_entry *entry, struct pt_regs *regs) * interrupt context, so if the access faults, we read the page tables * to find which page (if any) is mapped and access it directly. */ -static int read_user_stack_slow(void __user *ptr, void *ret, int nb) +static int read_user_stack_slow(void __user *ptr, void *buf, int nb) { + int ret = -EFAULT; pgd_t *pgdir; pte_t *ptep, pte; unsigned shift; unsigned long addr = (unsigned long) ptr; unsigned long offset; - unsigned long pfn; + unsigned long pfn, flags; void *kaddr; pgdir = current->mm->pgd; if (!pgdir) return -EFAULT; + local_irq_save(flags); ptep = find_linux_pte_or_hugepte(pgdir, addr, &shift); + if (!ptep) + goto err_out; if (!shift) shift = PAGE_SHIFT; /* align address to page boundary */ offset = addr & ((1UL << shift) - 1); - addr -= offset; - if (ptep == NULL) - return -EFAULT; - pte = *ptep; + pte = READ_ONCE(*ptep); if (!pte_present(pte) || !(pte_val(pte) & _PAGE_USER)) - return -EFAULT; + goto err_out; pfn = pte_pfn(pte); if (!page_is_ram(pfn)) - return -EFAULT; + goto err_out; /* no highmem to worry about here */ kaddr = pfn_to_kaddr(pfn); - memcpy(ret, kaddr + offset, nb); - return 0; + memcpy(buf, kaddr + offset, nb); + ret = 0; +err_out: + local_irq_restore(flags); + return ret; } static int read_user_stack_64(unsigned long __user *ptr, unsigned long *ret)