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authorAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>2015-03-30 10:41:03 +0530
committerMichael Ellerman <mpe@ellerman.id.au>2015-04-17 11:23:39 +1000
commit691e95fd7396905a38d98919e9c150dbc3ea21a3 (patch)
treed89b898d4f42d167f0da169f482d7104b46870d8 /arch/powerpc/include/asm
parentdac5657067919161eb3273ca787d8ae9814801e7 (diff)
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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 <aneesh.kumar@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/include/asm')
-rw-r--r--arch/powerpc/include/asm/pgtable.h11
1 files changed, 10 insertions, 1 deletions
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__ */
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