[PATCH v4 2/2] mm/memory-failure: teach kill_accessing_process to accept hugetlb tail page pfn

[Jane Chu <jane.chu@oracle.com>]

When a hugetlb folio is being poisoned again, try_memory_failure_hugetlb()
passed head pfn to kill_accessing_process(), that is not right.
The precise pfn of the poisoned page should be used in order to
determine the precise vaddr as the SIGBUS payload.

This issue has already been taken care of in the normal path, that is,
hwpoison_user_mappings(), see [1][2].  Further more, for [3] to work
correctly in the hugetlb repoisoning case, it's essential to inform
VM the precise poisoned page, not the head page.

[1] https://lkml.kernel.org/r/20231218135837.3310403-1-willy@infradead.org
[2] https://lkml.kernel.org/r/20250224211445.2663312-1-jane.chu@oracle.com
[3] https://lore.kernel.org/lkml/20251116013223.1557158-1-jiaqiyan@google.com/

Cc: <stable@vger.kernel.org>
Signed-off-by: Jane Chu <jane.chu@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
v4 -> v3: No change.
v2 -> v3:
  incorporated suggestions from Miaohe and Matthew.
v1 -> v2:
  pickup R-B, add stable to cc list.
---
 mm/memory-failure.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index b3e27451d618..885dc1d4f212 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -692,6 +692,8 @@ static int check_hwpoisoned_entry(pte_t pte, unsigned long addr, short shift,
 				unsigned long poisoned_pfn, struct to_kill *tk)
 {
 	unsigned long pfn = 0;
+	unsigned long hwpoison_vaddr;
+	unsigned long mask;
 
 	if (pte_present(pte)) {
 		pfn = pte_pfn(pte);
@@ -702,10 +704,12 @@ static int check_hwpoisoned_entry(pte_t pte, unsigned long addr, short shift,
 			pfn = softleaf_to_pfn(entry);
 	}
 
-	if (!pfn || pfn != poisoned_pfn)
+	mask = ~((1UL << (shift - PAGE_SHIFT)) - 1);
+	if (!pfn || ((pfn & mask) != (poisoned_pfn & mask)))
 		return 0;
 
-	set_to_kill(tk, addr, shift);
+	hwpoison_vaddr = addr + ((poisoned_pfn - pfn) << PAGE_SHIFT);
+	set_to_kill(tk, hwpoison_vaddr, shift);
 	return 1;
 }
 
@@ -2049,10 +2053,8 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
 		return action_result(pfn, MF_MSG_GET_HWPOISON, MF_IGNORED);
 	case MF_HUGETLB_FOLIO_PRE_POISONED:
 	case MF_HUGETLB_PAGE_PRE_POISON:
-		if (flags & MF_ACTION_REQUIRED) {
-			folio = page_folio(p);
-			res = kill_accessing_process(current, folio_pfn(folio), flags);
-		}
+		if (flags & MF_ACTION_REQUIRED)
+			res = kill_accessing_process(current, pfn, flags);
 		if (res == MF_HUGETLB_FOLIO_PRE_POISONED)
 			action_result(pfn, MF_MSG_ALREADY_POISONED, MF_FAILED);
 		else
-- 
2.43.5