Re: [PATCH 2/2] powerpc/64s: __find_linux_pte synchronization vs pmdp_invalidate
From: Aneesh Kumar K.V <hidden>
Date: 2019-06-07 05:41:14
Nicholas Piggin [off-list ref] writes:
The change to pmdp_invalidate to mark the pmd with _PAGE_INVALID broke the synchronisation against lock free lookups, __find_linux_pte's pmd_none check no longer returns true for such cases. Fix this by adding a check for this condition as well.
Reviewed-by: Aneesh Kumar K.V <redacted>
quoted hunk ↗ jump to hunk
Fixes: da7ad366b497 ("powerpc/mm/book3s: Update pmd_present to look at _PAGE_PRESENT bit") Cc: Christophe Leroy <redacted> Suggested-by: Aneesh Kumar K.V <redacted> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/mm/pgtable.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c index db4a6253df92..533fc6fa6726 100644 --- a/arch/powerpc/mm/pgtable.c +++ b/arch/powerpc/mm/pgtable.c@@ -372,13 +372,25 @@ pte_t *__find_linux_pte(pgd_t *pgdir, unsigned long ea, pdshift = PMD_SHIFT; pmdp = pmd_offset(&pud, ea); pmd = READ_ONCE(*pmdp); + /* - * A hugepage collapse is captured by pmd_none, because - * it mark the pmd none and do a hpte invalidate. + * A hugepage collapse is captured by this condition, see + * pmdp_collapse_flush. */ if (pmd_none(pmd)) return NULL; +#ifdef CONFIG_PPC_BOOK3S_64 + /* + * A hugepage split is captured by this condition, see + * pmdp_invalidate. + * + * Huge page modification can be caught here too. + */ + if (pmd_is_serializing(pmd)) + return NULL; +#endif + if (pmd_trans_huge(pmd) || pmd_devmap(pmd)) { if (is_thp) *is_thp = true;-- 2.20.1