[PATCH RFC 01/13] mm/hmm: Process pud swap entry without pud_huge()

peterx
2024-03-06T10:42:10Z

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(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index 277ddcab4947..c44391a0246e 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -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)) {
spin_unlock(ptl);
return hmm_vma_walk_hole(start, end, -1, walk);
}
@@ -435,11 +435,6 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
unsigned long *hmm_pfns;
unsigned long cpu_flags;

- if (!pud_present(pud)) {
- spin_unlock(ptl);
- return hmm_vma_walk_hole(start, end, -1, walk);
- }
-
i = (addr - range->start) >> PAGE_SHIFT;
npages = (end - addr) >> PAGE_SHIFT;
hmm_pfns = &range->hmm_pfns[i];
--
2.44.0