+ mm-memory-failure-fix-infinite-uce-for-vm_pfnmaped-page.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/memory-failure: fix infinite UCE for VM_PFNMAP'ed page
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-memory-failure-fix-infinite-uce-for-vm_pfnmaped-page.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-failure-fix-infinite-uce-for-vm_pfnmaped-page.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Jinjiang Tu <tujinjiang@huawei.com>
Subject: mm/memory-failure: fix infinite UCE for VM_PFNMAP'ed page
Date: Mon, 11 Aug 2025 12:33:23 +0800

When memory_failure() is called for a already hwpoisoned pfn backed with
struct page, kill_accessing_process() will conditionally send a SIGBUS to
the current (triggering) process if it maps the page.

However, in case the page is not ordinarily mapped, but was mapped through
remap_pfn_range(), kill_accessing_process() wouldn't identify it as mapped
even though hwpoison_pte_range() would be prepared to handle it, because
walk_page_range() will skip VM_PFNMAP as default in walk_page_test().  As
a result, walk_page_range() will return 0, assuming "not mapped" and
SIGBUS will be skipped.  The user task will trigger UCE infinitely because
it will not receive a SIGBUS on access and simply retry.

Before commit aaf99ac2ceb7 ("mm/hwpoison: do not send SIGBUS to processes
with recovered clean pages"), kill_accessing_process() will return EFAULT.
For x86, the current task will be killed in kill_me_maybe().

To fix it, add .test_walk callback for hwpoison_walk_ops to process
VM_PFNMAP VMAs too.

Link: https://lkml.kernel.org/r/20250811043323.899130-1-tujinjiang@huawei.com
Fixes: aaf99ac2ceb7 ("mm/hwpoison: do not send SIGBUS to processes with recovered clean pages")
Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Shuai Xue <xueshuai@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory-failure.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/mm/memory-failure.c~mm-memory-failure-fix-infinite-uce-for-vm_pfnmaped-page
+++ a/mm/memory-failure.c
@@ -853,9 +853,16 @@ static int hwpoison_hugetlb_range(pte_t
 #define hwpoison_hugetlb_range	NULL
 #endif
 
+static int hwpoison_test_walk(unsigned long start, unsigned long end,
+			     struct mm_walk *walk)
+{
+	return 0;
+}
+
 static const struct mm_walk_ops hwpoison_walk_ops = {
 	.pmd_entry = hwpoison_pte_range,
 	.hugetlb_entry = hwpoison_hugetlb_range,
+	.test_walk = hwpoison_test_walk,
 	.walk_lock = PGWALK_RDLOCK,
 };
 
_

Patches currently in -mm which might be from tujinjiang@huawei.com are

mm-memory-failure-fix-infinite-uce-for-vm_pfnmaped-page.patch
mm-memory_hotplug-fix-hwpoisoned-large-folio-handling-in-do_migrate_range.patch