From 691e95fd7396905a38d98919e9c150dbc3ea21a3 Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Mon, 30 Mar 2015 10:41:03 +0530 Subject: 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 --- arch/powerpc/include/asm/pgtable.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'arch/powerpc/include/asm') diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h index 92fe01c..11a3863 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__ */ -- cgit v1.1