Re: [RFC PATCH] powerpc/64s: __find_linux_pte synchronization vs pmdp_invalidate
From: Christophe Leroy <hidden>
Date: 2019-06-03 07:46:03
Le 03/06/2019 à 08:44, Nicholas Piggin a écrit :
quoted hunk ↗ jump to hunk
The pmd_none check does not catch hugepage collapse, nor does the pmd_present check in pmd_trans_huge, because hugepage collapse sets !_PAGE_PRESENT && _PAGE_INVALID (which results in !pmd_none and pmd_present). Aneesh noticed we might need this check as well. --- arch/powerpc/mm/pgtable.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-)diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c index db4a6253df92..7a702d21400a 100644 --- a/arch/powerpc/mm/pgtable.c +++ b/arch/powerpc/mm/pgtable.c@@ -372,13 +372,20 @@ 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. - */ + if (pmd_none(pmd)) return NULL; +#ifdef CONFIG_PPC_BOOK3S_64
I can't see anything that would build fail on other subarches. Wouldn't be better to use if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && (pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_INVALID) == _PAGE_INVALID))
+ if (pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_INVALID) == _PAGE_INVALID) {Maybe using pmd_raw() instead as in all the book3s64 helpers ? Christophe
+ /*
+ * A hugepage collapse is captured by this condition, see
+ * pmdp_invalidate.
+ */
+ return NULL;
+ }
+#endif
+
if (pmd_trans_huge(pmd) || pmd_devmap(pmd)) {
if (is_thp)
*is_thp = true;