From: Ryan Roberts ryan.roberts@arm.com
mainline inclusion from mainline-v6.9-rc1 commit 94c18d5f7e0d612ce3fb9cb4aa8cfb1308d57a0a category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I9OCYO CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
--------------------------------
Make clear the atmicity/consistency requirements of the API and how we achieve them.
Link: https://lore.kernel.org/linux-mm/Zc-Tqqfksho3BHmU@arm.com/ Link: https://lkml.kernel.org/r/20240226120321.1055731-3-ryan.roberts@arm.com Signed-off-by: Ryan Roberts ryan.roberts@arm.com Acked-by: David Hildenbrand david@redhat.com Reviewed-by: Catalin Marinas catalin.marinas@arm.com Cc: John Hubbard jhubbard@nvidia.com Cc: Mark Rutland mark.rutland@arm.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Liu Shixin liushixin2@huawei.com --- arch/arm64/mm/contpte.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c index be0a226c4ff9..1b64b4c3f8bf 100644 --- a/arch/arm64/mm/contpte.c +++ b/arch/arm64/mm/contpte.c @@ -183,16 +183,20 @@ EXPORT_SYMBOL_GPL(contpte_ptep_get); pte_t contpte_ptep_get_lockless(pte_t *orig_ptep) { /* - * Gather access/dirty bits, which may be populated in any of the ptes - * of the contig range. We may not be holding the PTL, so any contiguous - * range may be unfolded/modified/refolded under our feet. Therefore we - * ensure we read a _consistent_ contpte range by checking that all ptes - * in the range are valid and have CONT_PTE set, that all pfns are - * contiguous and that all pgprots are the same (ignoring access/dirty). - * If we find a pte that is not consistent, then we must be racing with - * an update so start again. If the target pte does not have CONT_PTE - * set then that is considered consistent on its own because it is not - * part of a contpte range. + * The ptep_get_lockless() API requires us to read and return *orig_ptep + * so that it is self-consistent, without the PTL held, so we may be + * racing with other threads modifying the pte. Usually a READ_ONCE() + * would suffice, but for the contpte case, we also need to gather the + * access and dirty bits from across all ptes in the contiguous block, + * and we can't read all of those neighbouring ptes atomically, so any + * contiguous range may be unfolded/modified/refolded under our feet. + * Therefore we ensure we read a _consistent_ contpte range by checking + * that all ptes in the range are valid and have CONT_PTE set, that all + * pfns are contiguous and that all pgprots are the same (ignoring + * access/dirty). If we find a pte that is not consistent, then we must + * be racing with an update so start again. If the target pte does not + * have CONT_PTE set then that is considered consistent on its own + * because it is not part of a contpte range. */
pgprot_t orig_prot;