There is a comment in hugetlb_fault() that does not hold anymore. This
one:
/*
* vmf.orig_pte could be a migration/hwpoison vmf.orig_pte at this
* point, so this check prevents the kernel from going below assuming
* that we have an active hugepage in pagecache. This goto expects
* the 2nd page fault, and is_hugetlb_entry_(migration|hwpoisoned)
* check will properly handle it.
*/
This was written because back in the day we used to do:
hugetlb_fault () {
ptep = huge_pte_offset(...)
if (ptep) {
entry = huge_ptep_get(ptep)
if (unlikely(is_hugetlb_entry_migration(entry))
...
else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
...
}
...
...
/*
* entry could be a migration/hwpoison entry at this point, so this
* check prevents the kernel from going below assuming that we have
* a active hugepage in pagecache. This goto expects the 2nd page fault,
* and is_hugetlb_entry_(migration|hwpoisoned) check will properly
* handle it.
*/
if (!pte_present(entry))
goto out_mutex;
...
}
The code was designed to check for hwpoisoned/migration entries upfront,
and then bail out if further down the pte was not present anymore, relying
on the second fault to properly handle migration/hwpoison entries that
time around.
The way we handle this is different nowadays, so drop the misleading
comment.
Link: https://lkml.kernel.org/r/20250627102904.107202-5-osalvador@suse.de
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gavin Guo <gavinguo@igalia.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/hugetlb.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 67f3c9c16348..ba078aa1cb96 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6745,13 +6745,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
ret = 0;
- /*
- * vmf.orig_pte could be a migration/hwpoison vmf.orig_pte at this
- * point, so this check prevents the kernel from going below assuming
- * that we have an active hugepage in pagecache. This goto expects
- * the 2nd page fault, and is_hugetlb_entry_(migration|hwpoisoned)
- * check will properly handle it.
- */
+ /* Not present, either a migration or a hwpoisoned entry */
if (!pte_present(vmf.orig_pte)) {
if (unlikely(is_hugetlb_entry_migration(vmf.orig_pte))) {
/*
--
2.50.0