The patch below does not apply to the 5.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a00196a272161338d4b1d66ec69e3d57c6b280e0 Mon Sep 17 00:00:00 2001

From: Nicholas Piggin npiggin@gmail.com Date: Fri, 7 Jun 2019 13:56:36 +1000 Subject: [PATCH] powerpc/64s: __find_linux_pte() synchronization vs pmdp_invalidate()

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.

Fixes: da7ad366b497 ("powerpc/mm/book3s: Update pmd_present to look at _PAGE_PRESENT bit") Cc: stable@vger.kernel.org # v4.20+ Suggested-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Signed-off-by: Nicholas Piggin npiggin@gmail.com Reviewed-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au

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;