Re: [PATCH RFC 01/13] mm/hmm: Process pud swap entry without pud_huge()
From: Jason Gunthorpe <jgg@nvidia.com>
Date: 2024-03-07 18:12:37
Also in:
linux-arm-kernel, linux-mm, lkml, sparclinux
On Wed, Mar 06, 2024 at 06:41:35PM +0800, peterx@redhat.com wrote:
From: Peter Xu <peterx@redhat.com> Swap pud entries do not always return true for pud_huge() for all archs. x86 and sparc (so far) allow it, but all the rest do not accept a swap entry to be reported as pud_huge(). So it's not safe to check swap entries within pud_huge(). Check swap entries before pud_huge(), so it should be always safe. This is the only place in the kernel that (IMHO, wrongly) relies on pud_huge() to return true on pud swap entries. The plan is to cleanup pXd_huge() to only report non-swap mappings for all archs. Cc: Alistair Popple <apopple@nvidia.com> Signed-off-by: Peter Xu <peterx@redhat.com> --- mm/hmm.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-)
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
quoted hunk ↗ jump to hunk
@@ -424,7 +424,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end, walk->action = ACTION_CONTINUE; pud = READ_ONCE(*pudp); - if (pud_none(pud)) { + if (pud_none(pud) || !pud_present(pud)) {
Isn't this a tautology? pud_none always implies !present() ? Jason