Commit a00196a2 authored Jun 07, 2019 by Nicholas Piggin Committed by Michael Ellerman Jun 07, 2019

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: da7ad366 ("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>

parent 33258a1d

arch/powerpc/mm/pgtable.c

+14 −2

Original line number	Diff line number	Diff line
		@@ -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;

Admin message