[PATCH v6 0/5] Only free healthy pages in high-order has_hwpoisoned folio

[PATCH v6 0/5] Only free healthy pages in high-order has_hwpoisoned folio

[Jiaqi Yan]

At the end of dissolve_free_hugetlb_folio(), a free HugeTLB
folio becomes non-HugeTLB and is released to buddy allocator
as a high-order folio, e.g. a folio that contains 262144 pages
if the folio was a 1G HugeTLB hugepage.

This is problematic if the HugeTLB hugepage contained HWPoison
subpages. In that case, since buddy allocator does not check
HWPoison for non-zero-order folio, the raw HWPoison page can
be given out with its buddy page and be re-used by either
kernel or userspace.

Memory failure recovery (MFR) code (mm/memory-failure.c) does
attempt to take raw HWPoison page off buddy allocator after
dissolve_free_hugetlb_folio(). However, there is always a time
window between dissolve_free_hugetlb_folio() frees a HWPoison
high-order folio to buddy allocator and MFR takes HWPoison
raw page off buddy allocator.

Another similar situation is when a transparent huge page (THP)
is handled by MFR but splitting failed. Such THP will eventually
be released to buddy allocator when owning userspace processes
are gone, but with certain subpages having HWPoison [9].

One obvious way to avoid both problems is to add page sanity
checks in page allocate or free path. However, it is against
the past efforts to reduce sanity check overhead [1,2,3].

Introduce free_has_hwpoisoned() to only free the healthy pages
and exclude the HWPoison ones in the high-order folio.
free_has_hwpoisoned() happens at the end of free_pages_prepare(),
which already deals with both decomposing the original compound
page, updating page metadata like alloc tag and page owner.
It is also only applied when PG_has_hwpoisoned indicates folio
contains certain HWPoison page(s) for performance reason.
Its idea is to iterate through the sub-pages of the folio to
identify contiguous ranges of healthy pages. Instead of freeing
pages one by one, free_has_hwpoisoned() then re-use
free_prepared_contig_range() [11] to decompose healthy ranges into
the largest possible chunks of different orders. Every chunk is
freed via __free_frozen_pages().

free_has_hwpoisoned() has linear time complexity wrt the number
of pages in the folio. While the power-of-two decomposition
ensures that the number of calls to the buddy allocator is
logarithmic for each contiguous healthy range, the mandatory
linear scan of pages to identify PageHWPoison() defines the
overall time complexity.

I tested with some test-only code [4] and hugetlb-mfr [5], by
checking the status of pcplist and freelist immediately after
dissolve_free_hugetlb_folio() a free 2M or 1G HugeTLB page that
contains 1~8 HWPoison raw pages:

- HWPoison pages are excluded by free_has_hwpoisoned().

- Some healthy pages can be in zone->per_cpu_pageset (pcplist)
  because pcp_count is not high enough. Many healthy pages are
  in some order's zone->free_area[order].free_list (freelist).

- In rare cases, some healthy pages are in neither pcplist
  nor freelist. My best guest is they are allocated before
  the test checks.

To illustrate the latency free_has_hwpoisoned() added to the
memory freeing path, I tested its time cost with 8 HWPoison
pages with instrument code in [4] for 20 sample runs on a machine
having 56 Intel Skylake physical cores and 768GB memory:

- Has HWPoison path: mean=1030us, stdev=21us

- No HWPoison path: mean=66us, stdev=6us

free_has_hwpoisoned() is around 15x the baseline. Its cost is
nontrivial, but still far from triggering soft lockup, and fair
for handling exceptional hardware memory errors.

Now that free_has_hwpoisoned() ensures HWPoison pages never made
into buddy allocator, MFR don't need to take_page_off_buddy() anymore
after disovling HWPoison hugepages. So replace __page_handle_poison()
with new __hugepage_handle_poison() for HugeTLB specific call sites.
It may worthy to note that this patchset doesn't affect the soft
offline behavior in MFR. This is because soft offline does not
folio_set_hwpoison() upfront, and for HugeTLB case, doesn't involve
get_huge_page_for_hwpoison().

To provide test coverage for the new __hugepage_handle_poison()
in me_huge_page(), the last commit adds a MADV_HARD test variant
for anonymous HugeTLB pages. It also cover the code path that
frees a HugeTLB page that contains 1 raw HWPoison page.

Based on commit cfb8731f5396 ("mm: fix CONFIG_STACK_GROWSUP typo in tools/testing/vma/include/dup.h")

Changelog

v5 [11] -> v6

- Rebase to recent akpm/mm-unstable and address comments from Zi Yan,
  Miaohe Lin, Vlastimil Babka.

- Extract free_pages_sanitize() to avoid touching HWPoison page(s)
  at the end of __free_pages_prepare().

- Introduce FPI_SANITIZE and add a fpi_t argument to the freeing path
  free_has_hwpoisoned() -> __free_prepared_contig_range(), so that
  healthy page blocks are sanitized before __free_frozen_pages().

- Make free_has_hwpoisoned() be compatible with order==0.

- Repeat the previous test done on both X86 and ARM64 machines.
  CONFIG_KASAN + CONFIG_KASAN_SW_TAGS + kasan.fault=report are
  enabled on the ARM64 machine.

v4 [10] -> v5

- Rebase to very recent akpm/mm-unstable.

- Re-use free_prepared_contig_range() introduced by [11], and remove
  free_contiguous_pages() in v4.

- Instead of using struct page pointer, iterate over pfn in
  free_has_hwpoison().

- Re-ested and re-evaluated free_has_hwpoison()'s time cost.

- Add memory failure recovery test for anonymous 1G HugeTLB page to
  gain test coverage for __hugepage_handle_poison() and for freeing
  1G HugeTLB page that has 1 HWPoison page.

v3 [8] -> v4

- Address comments from Zi Yan, Miaohe Lin, Harry Yoo.

- Set has_hwpoisoned flag after introducing free_has_hwpoisoned().

- Unwrap free_pages_prepare_has_hwpoisoned() into free_pages_prepare().

- If folio has HWPoison, its healthy pages will be freed with FPI_NONE
  right in free_pages_prepare(), who returns false to indicate caller
  should not proceeding its own freeing action.

- Rework the commit on __page_handle_poison. Only change the handling
  for HWPoison HugeTLB page, leaving free buddy page and soft offline
  handling alone.

v2 [7] -> v3:

- Address comments from Mathew Wilcox, Harry Hoo, Miaohe Lin.

- Let free_has_hwpoisoned() happen after free_pages_prepare(),
  which help to deal with decomposing the original compound page,
  and with page metadata like alloc tag and page owner.

- Tested with "page_owner=on" and CONFIG_MEM_ALLOC_PROFILING*=y.

- Wrap checking PG_has_hwpoisoned and free_has_hwpoisoned() into
  free_pages_prepare_has_hwpoisoned(), which replaces
  free_pages_prepare() calls in free_frozen_pages().

- Rename free_has_hwpoison_page() to free_has_hwpoisoned().

- Measure latency added by free_has_hwpoisoned().

- Ensure struct page *end is only used for pointer arithmetic,
  instead of accessed as page.

- Refactor page_handl_poison instead of just __page_handle_poison().

v1 [6] -> v2:

- Total reimplementation based on discussions with Mathew Wilcox,
  Harry Hoo, Zi Yan etc

- hugetlb_free_hwpoison_folio() => free_has_hwpoison_pages().

- Utilize has_hwpoisoned flag to tell buddy allocator a high-order
  folio contains HWPoison.

- Simplify __page_handle_poison() given that the HWPoison page(s)
  won't be freed within high-order folio.

[1] https://lore.kernel.org/linux-mm/1460711275-1130-15-git-send-email-mgorman@techsingularity.net
[2] https://lore.kernel.org/linux-mm/1460711275-1130-16-git-send-email-mgorman@techsingularity.net
[3] https://lore.kernel.org/all/20230216095131.17336-1-vbabka@suse.cz
[4] https://drive.google.com/file/d/1CzJn1Cc4wCCm183Y77h244fyZIkTLzCt/view?usp=sharing
[5] https://lore.kernel.org/linux-mm/20251116013223.1557158-3-jiaqiyan@google.com
[6] https://lore.kernel.org/linux-mm/20251116014721.1561456-1-jiaqiyan@google.com
[7] https://lore.kernel.org/linux-mm/20251219183346.3627510-1-jiaqiyan@google.com
[8] https://lore.kernel.org/linux-mm/20260112004923.888429-1-jiaqiyan@google.com
[9] https://lore.kernel.org/linux-mm/20260113205441.506897-1-boudewijn@delta-utec.com
[10] https://lore.kernel.org/linux-mm/20260202194125.2191216-1-jiaqiyan@google.com
[11] https://lore.kernel.org/all/20260401101634.2868165-2-usama.anjum@arm.com
[12] https://lore.kernel.org/linux-mm/20260531055829.3636554-1-jiaqiyan@google.com

Jiaqi Yan (5):
  mm/page_alloc: introduce __free_prepared_contig_range() with fpi_t
  mm/page_alloc: only free healthy pages in high-order has_hwpoisoned
    folio
  mm/memory-failure: set has_hwpoisoned flags on dissolved HugeTLB folio
  mm/memory-failure: skip take_page_off_buddy after dissolving HWPoison
    HugeTLB page
  selftests/mm: add hard memory failure anonymous HugeTLB test

 include/linux/page-flags.h                  |   2 +-
 mm/memory-failure.c                         |  37 +++-
 mm/page_alloc.c                             | 176 ++++++++++++++++----
 tools/testing/selftests/mm/memory-failure.c |  70 +++++++-
 4 files changed, 247 insertions(+), 38 deletions(-)

-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v6 1/5] mm/page_alloc: introduce __free_prepared_contig_range() with fpi_t

[Jiaqi Yan]

A future commit introducing free_has_hwpoison() to be called within
__free_pages_prepare() will need to pass specific fpi_t flags when
freeing a contiguous range of pages. Currently,
free_prepared_contig_range() hardcodes the FPI_PREPARED flag and
does not accept any caller-provided flags.

Rename the core logic to __free_prepared_contig_range() to accept
an fpi_t argument. It bitwise ORs with the required FPI_PREPARED
flag.

This is a preparatory commit with no functional changes.

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 mm/page_alloc.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 762d9b6bc792..7d27aff48b15 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6852,8 +6852,8 @@ void __init page_alloc_sysctl_init(void)
 	register_sysctl_init("vm", page_alloc_sysctl_table);
 }
 
-static void free_prepared_contig_range(struct page *page,
-		unsigned long nr_pages)
+static void __free_prepared_contig_range(struct page *page,
+		unsigned long nr_pages, fpi_t fpi_flags)
 {
 	unsigned long pfn = page_to_pfn(page);
 
@@ -6870,7 +6870,7 @@ static void free_prepared_contig_range(struct page *page,
 		 * Free the chunk as a single block. Our caller has already
 		 * called free_pages_prepare() for each order-0 page.
 		 */
-		__free_frozen_pages(page, order, FPI_PREPARED);
+		__free_frozen_pages(page, order, fpi_flags | FPI_PREPARED);
 
 		pfn += 1UL << order;
 		page += 1UL << order;
@@ -6878,6 +6878,11 @@ static void free_prepared_contig_range(struct page *page,
 	}
 }
 
+static void free_prepared_contig_range(struct page *page, unsigned long nr_pages)
+{
+	__free_prepared_contig_range(page, nr_pages, FPI_NONE);
+}
+
 static void __free_contig_range_common(unsigned long pfn, unsigned long nr_pages,
 		bool is_frozen)
 {
-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v6 2/5] mm/page_alloc: only free healthy pages in high-order has_hwpoisoned folio

[Jiaqi Yan]

At the end of dissolve_free_hugetlb_folio(), a free HugeTLB folio
becomes non-HugeTLB, and it is released to buddy allocator
as a high-order folio, e.g. a folio that contains 262144 pages
if the folio was a 1G HugeTLB hugepage.

This is problematic if the HugeTLB hugepage contained HWPoison
subpages. In that case, since buddy allocator does not check
HWPoison for non-zero-order folio, the raw HWPoison page can
be given out with its buddy page and be re-used by either
kernel or userspace.

Memory failure recovery (MFR) in kernel does attempt to take
raw HWPoison page off buddy allocator after
dissolve_free_hugetlb_folio(). However, there is always a time
window between dissolve_free_hugetlb_folio() frees a HWPoison
high-order folio to buddy allocator and MFR takes HWPoison
raw page off buddy allocator.

Another similar situation is when a transparent huge page (THP)
runs into memory failure but splitting failed. Such THP will
eventually be released to buddy allocator when owning userspace
processes are gone, but with certain subpages having HWPoison.

One obvious way to avoid both problems is to add page sanity
checks in page allocate or free path. However, it is against
the past efforts to reduce sanity check overhead [1,2,3].

Introduce free_has_hwpoisoned() to only free the healthy pages
and to exclude the HWPoison ones in the high-order folio.
The idea is to iterate through the sub-pages of the folio to
identify contiguous ranges of healthy pages.

free_has_hwpoisoned() is added at the end of __free_pages_prepare()
as a shortcut and only if PG_has_hwpoisoned indicates HWPoison page
exists and after checks and preparations in __free_pages_prepare()
all succeeded. It then use __free_prepared_contig_range() to
decompose healthy range into the largest possible chunks of
different orders, then freed via __free_frozen_pages().

free_has_hwpoisoned() has linear time complexity wrt the number
of pages in the folio. While the power-of-two decomposition
ensures that the number of calls to the buddy allocator is
logarithmic for each contiguous healthy range, the mandatory
linear scan of pages to identify PageHWPoison() defines the
overall time complexity. For a 1G hugepage having 8 HWPoison
pages, free_has_hwpoisoned() takes around 1ms on average on
a system having 56 Intel Skylake physical cores. This is
15x to the case of freeing no HWPoison page. The cost is far
from triggering soft lockup, and fair for handling exceptional
hardware memory errors.

[1] https://lore.kernel.org/linux-mm/1460711275-1130-15-git-send-email-mgorman@techsingularity.net
[2] https://lore.kernel.org/linux-mm/1460711275-1130-16-git-send-email-mgorman@techsingularity.net
[3] https://lore.kernel.org/all/20230216095131.17336-1-vbabka@suse.cz

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 mm/page_alloc.c | 165 ++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 140 insertions(+), 25 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7d27aff48b15..6418896c9df6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -93,6 +93,13 @@ typedef int __bitwise fpi_t;
 /* free_pages_prepare() has already been called for page(s) being freed. */
 #define FPI_PREPARED		((__force fpi_t)BIT(3))
 
+/*
+ * Page(s) needs to go through free_pages_sanitize(), for example, because
+ * free_pages_prepare() cannot sanitize a high-order page block due to
+ * hardware error in some page(s).
+ */
+#define FPI_SANITIZE		((__force fpi_t)BIT(4))
+
 /* prevent >1 _updater_ of zone percpu pageset ->high and ->batch fields */
 static DEFINE_MUTEX(pcp_batch_high_lock);
 #define MIN_PERCPU_PAGELIST_HIGH_FRACTION (8)
@@ -210,6 +217,8 @@ gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
 unsigned int pageblock_order __read_mostly;
 #endif
 
+static void free_has_hwpoisoned(struct page *page, unsigned int order,
+				fpi_t fpi_flags);
 static void __free_pages_ok(struct page *page, unsigned int order,
 			    fpi_t fpi_flags);
 static void reserve_highatomic_pageblock(struct page *page, int order,
@@ -1311,14 +1320,73 @@ static inline void pgalloc_tag_sub_pages(struct alloc_tag *tag, unsigned int nr)
 
 #endif /* CONFIG_MEM_ALLOC_PROFILING */
 
+/*
+ * Sanitize, which requires writing, a block of pages at the last moment of
+ * preparing to freeing them, i.e. __free_pages_prepare().
+ */
+static void free_pages_sanitize(struct page *page, unsigned int order)
+{
+	bool init = want_init_on_free();
+	/*
+	 * __kasan_unpoison_pages() sets kasan tag on every tail page, so
+	 * it is fine to use should_skip_kasan_poison() when pages here
+	 * were a set of tail pages from a compound folio.
+	 */
+	bool skip_kasan_poison = should_skip_kasan_poison(page);
+
+	kernel_poison_pages(page, 1 << order);
+
+	/*
+	 * As memory initialization might be integrated into KASAN,
+	 * KASAN poisoning and memory initialization code must be
+	 * kept together to avoid discrepancies in behavior.
+	 *
+	 * With hardware tag-based KASAN, memory tags must be set before the
+	 * page becomes unavailable via debug_pagealloc or arch_free_page.
+	 */
+	if (!skip_kasan_poison) {
+		kasan_poison_pages(page, order, init);
+
+		/* Memory is already initialized if KASAN did it internally. */
+		if (kasan_has_integrated_init())
+			init = false;
+	}
+	if (init)
+		clear_highpages_kasan_tagged(page, 1 << order);
+
+	/*
+	 * arch_free_page() can make the page's contents inaccessible.  s390
+	 * does this.  So nothing which can access the page's contents should
+	 * happen after this.
+	 */
+	arch_free_page(page, order);
+
+	debug_pagealloc_unmap_pages(page, 1 << order);
+}
+
+/*
+ * Returns
+ * - true: checks and preparations all good, caller can proceed freeing.
+ * - false: do not proceed freeing for one of the following reasons:
+ *   1. Some check failed so it is not safe to proceed freeing.
+ *   2. A compound page has some HWPoison pages. The healthy pages
+ *      are already safely freed, and the HWPoison ones isolated.
+ */
 static __always_inline bool __free_pages_prepare(struct page *page,
 		unsigned int order, fpi_t fpi_flags)
 {
 	int bad = 0;
-	bool skip_kasan_poison = should_skip_kasan_poison(page);
-	bool init = want_init_on_free();
 	bool compound = PageCompound(page);
 	struct folio *folio = page_folio(page);
+	/*
+	 * When dealing with compound page, PG_has_hwpoisoned is cleared
+	 * with PAGE_FLAGS_SECOND. So the check must be done first.
+	 *
+	 * Note we can't exclude PG_has_hwpoisoned from PAGE_FLAGS_SECOND.
+	 * Because PG_has_hwpoisoned == PG_active, free_page_is_bad() will
+	 * confuse and complaint that the first tail page is still active.
+	 */
+	bool should_fhh = compound && folio_test_has_hwpoisoned(folio);
 
 	if (fpi_flags & FPI_PREPARED)
 		return true;
@@ -1416,34 +1484,19 @@ static __always_inline bool __free_pages_prepare(struct page *page,
 					   PAGE_SIZE << order);
 	}
 
-	kernel_poison_pages(page, 1 << order);
-
 	/*
-	 * As memory initialization might be integrated into KASAN,
-	 * KASAN poisoning and memory initialization code must be
-	 * kept together to avoid discrepancies in behavior.
+	 * After breaking down compound page and dealing with page metadata
+	 * (e.g. page owner and page alloc tags), take a shortcut if this
+	 * was a compound page containing certain HWPoison subpages.
 	 *
-	 * With hardware tag-based KASAN, memory tags must be set before the
-	 * page becomes unavailable via debug_pagealloc or arch_free_page.
+	 * FPI_SANITIZE to remember free_pages_sanitize() healthy pages.
 	 */
-	if (!skip_kasan_poison) {
-		kasan_poison_pages(page, order, init);
-
-		/* Memory is already initialized if KASAN did it internally. */
-		if (kasan_has_integrated_init())
-			init = false;
+	if (should_fhh) {
+		free_has_hwpoisoned(page, order, fpi_flags | FPI_SANITIZE);
+		return false;
 	}
-	if (init)
-		clear_highpages_kasan_tagged(page, 1 << order);
-
-	/*
-	 * arch_free_page() can make the page's contents inaccessible.  s390
-	 * does this.  So nothing which can access the page's contents should
-	 * happen after this.
-	 */
-	arch_free_page(page, order);
 
-	debug_pagealloc_unmap_pages(page, 1 << order);
+	free_pages_sanitize(page, order);
 
 	return true;
 }
@@ -6869,7 +6922,14 @@ static void __free_prepared_contig_range(struct page *page,
 		/*
 		 * Free the chunk as a single block. Our caller has already
 		 * called free_pages_prepare() for each order-0 page.
+		 *
+		 * If the original compound page has HWPoison page,
+		 * free_pages_prepare() has to skip sanitize at that time,
+		 * but now it is good time to do that.
 		 */
+		if (fpi_flags & FPI_SANITIZE)
+			free_pages_sanitize(page, order);
+
 		__free_frozen_pages(page, order, fpi_flags | FPI_PREPARED);
 
 		pfn += 1UL << order;
@@ -6956,6 +7016,61 @@ void __free_contig_range(unsigned long pfn, unsigned long nr_pages)
 	__free_contig_range_common(pfn, nr_pages, /* is_frozen= */ false);
 }
 
+/*
+ * Given some contiguous pages that have certain number of HWPoison page(s),
+ * free only the healthy ones.
+ *
+ * Used at the end of __free_pages_prepare(). Even if having HWPoison pages,
+ * breaking down compound page and clearing metadata (e.g. page owner, alloc
+ * tag) can be done together during __free_pages_prepare(), which simplifies
+ * the splitting here: unlike __split_unmapped_folio(), there is no need to
+ * turn split pages into a compound page or to carry metadata.
+ *
+ * It scans every raw page of the compound page and causes nontrivial overhead.
+ * So only use this when the compound page contains HWPoison page(s).
+ *
+ * It also works when order == 0, regardless of PageHWPoison() or not.
+ *
+ * This implementation needs rework in memdesc world.
+ */
+static void free_has_hwpoisoned(struct page *page, unsigned int order,
+				fpi_t fpi_flags)
+{
+	unsigned long curr = page_to_pfn(page);
+	unsigned long end_pfn = curr + (1 << order);
+	unsigned long next;
+	unsigned long total_freed = 0;
+	unsigned long total_hwp = 0;
+
+	while (curr < end_pfn) {
+		next = curr;
+
+		while (next < end_pfn && !PageHWPoison(pfn_to_page(next)))
+			++next;
+
+		if (next != end_pfn) {
+			/*
+			 * Avoid accounting error when the page is freed
+			 * by unpoison_memory().
+			 */
+			clear_page_tag_ref(pfn_to_page(next));
+			++total_hwp;
+		}
+
+		__free_prepared_contig_range(pfn_to_page(curr), next - curr,
+					     fpi_flags);
+		total_freed += next - curr;
+
+		if (next == end_pfn)
+			break;
+
+		curr = next + 1;
+	}
+
+	pr_info("Freed %#lx pages, excluded %#lx HWPoison pages\n",
+		total_freed, total_hwp);
+}
+
 #ifdef CONFIG_CONTIG_ALLOC
 /* Usage: See admin-guide/dynamic-debug-howto.rst */
 static void alloc_contig_dump_pages(struct list_head *page_list)
-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v6 3/5] mm/memory-failure: set has_hwpoisoned flags on dissolved HugeTLB folio

[Jiaqi Yan]

When a free HWPoison HugeTLB folio is dissolved, it becomes
non-HugeTLB and is released to buddy allocator as a high-order
folio.

Set has_hwpoisoned flags on the high-order folio so that buddy
allocator can tell that it contains certain HWPoison page(s),
and can handle it specially with free_has_hwpoisoned().

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
---
 include/linux/page-flags.h | 2 +-
 mm/memory-failure.c        | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 7a863572adce..3cd524e04a30 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -879,7 +879,7 @@ FOLIO_FLAG_FALSE(partially_mapped)
 
 #define PG_head_mask ((1UL << PG_head))
 
-#if defined(CONFIG_MEMORY_FAILURE) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
+#if defined(CONFIG_MEMORY_FAILURE) && (defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLB_PAGE))
 /*
  * PageHasHWPoisoned indicates that at least one subpage is hwpoisoned in the
  * compound page.
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 4916ab145325..3d15b4c1b694 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2008,6 +2008,7 @@ void folio_clear_hugetlb_hwpoison(struct folio *folio)
 	if (folio_test_hugetlb_vmemmap_optimized(folio))
 		return;
 	folio_clear_hwpoison(folio);
+	folio_set_has_hwpoisoned(folio);
 	folio_free_raw_hwp(folio, true);
 }
 
-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v6 4/5] mm/memory-failure: skip take_page_off_buddy after dissolving HWPoison HugeTLB page

[Jiaqi Yan]

Now that HWPoison subpage(s) within HugeTLB page will be rejected by
buddy allocator during dissolve_free_hugetlb_folio(), there is no
need to drain_all_pages() and take_page_off_buddy() anymore. In fact,
calling take_page_off_buddy() after dissolve_free_hugetlb_folio()
succeeded returns false, making caller think __page_handle_poison()
failed.

Add __hugepage_handle_poison() and replace __page_handle_poison() at
HugeTLB specific call sites. The being handled HugeTLB page either
is free at the moment of try_memory_failure_hugetlb(), or becomes
free at the moment of me_huge_page().

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 mm/memory-failure.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 3d15b4c1b694..a37b67550718 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -174,6 +174,30 @@ static struct rb_root_cached pfn_space_itree = RB_ROOT_CACHED;
 static DEFINE_MUTEX(pfn_space_lock);
 
 /*
+ * Only for a HugeTLB page being handled by memory_failure(). The key
+ * difference to soft_offline() is that, no HWPoison subpage will make
+ * into buddy allocator after a successful dissolve_free_hugetlb_folio(),
+ * so take_page_off_buddy() is unnecessary.
+ */
+static int __hugepage_handle_poison(struct page *page)
+{
+	struct folio *folio = page_folio(page);
+
+	/*
+	 * Can't use dissolve_free_hugetlb_folio() without a reliable
+	 * raw_hwp_list telling which subpage is HWPoison. So do not free
+	 * them to the buddy allocator. dequeue_hugetlb_folio_node_exact()
+	 * will ensure to never re-allocate this hugepage.
+	 */
+	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
+		/* raw_hwp_list becomes unreliable when kmalloc() fails. */
+		return -ENOMEM;
+
+	return dissolve_free_hugetlb_folio(folio);
+}
+
+/*
+ * Only for a free or HugeTLB page being handled by soft_offline().
  * Return values:
  *   1:   the page is dissolved (if needed) and taken off from buddy,
  *   0:   the page is dissolved (if needed) and not taken off from buddy,
@@ -1166,11 +1190,11 @@ static int me_huge_page(struct page_state *ps, struct page *p)
 		 * subpages.
 		 */
 		folio_put(folio);
-		if (__page_handle_poison(p) > 0) {
+		if (__hugepage_handle_poison(p)) {
+			res = MF_FAILED;
+		} else {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
-		} else {
-			res = MF_FAILED;
 		}
 	}
 
@@ -2133,11 +2157,11 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags)
 	 */
 	if (res == MF_HUGETLB_FREED) {
 		folio_unlock(folio);
-		if (__page_handle_poison(p) > 0) {
+		if (__hugepage_handle_poison(p)) {
+			res = MF_FAILED;
+		} else {
 			page_ref_inc(p);
 			res = MF_RECOVERED;
-		} else {
-			res = MF_FAILED;
 		}
 		return action_result(pfn, MF_MSG_FREE_HUGE, res);
 	}
-- 
2.55.0.rc0.799.gd6f94ed593-goog

[PATCH v6 5/5] selftests/mm: add hard memory failure anonymous HugeTLB test

[Jiaqi Yan]

Add a new testcase to validate memory failure recovery for HWPoison
anonymous HugeTLB page, including proper SIGBUS delivery, releasing
a HugeTLB page containing one HWPoison page to buddy allocator, and
isolation of the raw HWPoison page.

The test uses HugeTLB's default hugesize.

Although can be added in future, this patch does not support testing
the MADV_SOFT variant.

Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
---
 tools/testing/selftests/mm/memory-failure.c | 70 ++++++++++++++++++++-
 1 file changed, 67 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/mm/memory-failure.c b/tools/testing/selftests/mm/memory-failure.c
index 032ed952057c..78c105ce2af1 100644
--- a/tools/testing/selftests/mm/memory-failure.c
+++ b/tools/testing/selftests/mm/memory-failure.c
@@ -18,6 +18,7 @@
 #include <linux/magic.h>
 #include <errno.h>
 
+#include "hugepage_settings.h"
 #include "vm_util.h"
 
 enum inject_type {
@@ -27,6 +28,7 @@ enum inject_type {
 
 enum result_type {
 	MADV_HARD_ANON,
+	MADV_HARD_ANON_HUGETLB,
 	MADV_HARD_CLEAN_PAGECACHE,
 	MADV_HARD_DIRTY_PAGECACHE,
 	MADV_SOFT_ANON,
@@ -47,6 +49,8 @@ FIXTURE(memory_failure)
 	int pagemap_fd;
 	int kpageflags_fd;
 	bool triggered;
+	/* Number of initial HugeTLB pages with default page size. */
+	unsigned long nr_hugetlb_pages;
 };
 
 FIXTURE_VARIANT(memory_failure)
@@ -157,6 +161,7 @@ static void check(struct __test_metadata *_metadata, FIXTURE_DATA(memory_failure
 		  void *vaddr, enum result_type type, int setjmp)
 {
 	unsigned long size;
+	unsigned long nr_hugetlb_pages;
 	uint64_t pfn_flags;
 
 	switch (type) {
@@ -174,6 +179,7 @@ static void check(struct __test_metadata *_metadata, FIXTURE_DATA(memory_failure
 		ASSERT_NE(pagemap_get_pfn(self->pagemap_fd, vaddr), self->pfn);
 		break;
 	case MADV_HARD_ANON:
+	case MADV_HARD_ANON_HUGETLB:
 	case MADV_HARD_DIRTY_PAGECACHE:
 		/* The SIGBUS signal should have been received. */
 		ASSERT_EQ(setjmp, 1);
@@ -184,8 +190,15 @@ static void check(struct __test_metadata *_metadata, FIXTURE_DATA(memory_failure
 		ASSERT_EQ(1UL << siginfo.si_addr_lsb, self->page_size);
 		ASSERT_EQ(siginfo.si_addr, vaddr);
 
-		/* XXX Check backing pte is hwpoison entry when supported. */
-		ASSERT_TRUE(pagemap_is_swapped(self->pagemap_fd, vaddr));
+		if (type != MADV_HARD_ANON_HUGETLB)
+			/*
+			 * Check backing pte is hwpoison entry when supported.
+			 * Although try_to_unmap_one() also installs hwpoison
+			 * entry for HugeTLB, pagemap_hugetlb_range() doesn't
+			 * parse swap entries at all.
+			 */
+			ASSERT_TRUE(pagemap_is_swapped(self->pagemap_fd, vaddr));
+
 		break;
 	default:
 		SKIP(return, "unexpected inject type %d.\n", type);
@@ -193,7 +206,19 @@ static void check(struct __test_metadata *_metadata, FIXTURE_DATA(memory_failure
 
 	/* Check if the value of HardwareCorrupted has increased. */
 	ASSERT_EQ(get_hardware_corrupted_size(&size), 0);
-	ASSERT_EQ(size, self->corrupted_size + self->page_size / 1024);
+
+	if (type == MADV_HARD_ANON_HUGETLB) {
+		/*
+		 * Only one page is hardware corrupted; the rest should all be
+		 * released to buddy allocator.
+		 */
+		ASSERT_EQ(size, self->corrupted_size + getpagesize() / 1024);
+		/* HugeTLB should have lost the HWPoison HugeTLB page. */
+		nr_hugetlb_pages = hugetlb_nr_default_pages();
+		ASSERT_EQ(nr_hugetlb_pages + 1, self->nr_hugetlb_pages);
+	} else {
+		ASSERT_EQ(size, self->corrupted_size + self->page_size / 1024);
+	}
 
 	/* Check if HWPoison flag is set. */
 	ASSERT_EQ(pageflags_get(self->pfn, self->kpageflags_fd, &pfn_flags), 0);
@@ -247,6 +272,45 @@ TEST_F(memory_failure, anon)
 	ASSERT_EQ(munmap(addr, self->page_size), 0);
 }
 
+TEST_F(memory_failure, anon_hugetlb)
+{
+	char *addr;
+	int ret;
+	const unsigned long nr_alloc_hugetlb_pages = 4;
+	unsigned long alloc_size;
+
+	if (variant->type == MADV_SOFT)
+		SKIP(return, "Soft offline test is not implemented");
+
+	/* HugeTLB settings will be automatically restored when test exits. */
+	hugetlb_setup_default(nr_alloc_hugetlb_pages);
+
+	alloc_size = default_huge_page_size() * nr_alloc_hugetlb_pages;
+	self->page_size = default_huge_page_size();
+	self->nr_hugetlb_pages = hugetlb_nr_default_pages();
+
+	addr = mmap(0, alloc_size, PROT_READ | PROT_WRITE,
+		    MAP_ANONYMOUS | MAP_PRIVATE | MAP_HUGETLB, -1, 0);
+	if (addr == MAP_FAILED)
+		SKIP(return, "mmap failed, not enough memory or hugetlb not supported.\n");
+	memset(addr, 0xce, alloc_size);
+
+	prepare(_metadata, self, addr);
+
+	ret = sigsetjmp(signal_jmp_buf, 1);
+	if (!self->triggered) {
+		self->triggered = true;
+		ASSERT_EQ(variant->inject(self, addr), 0);
+		FORCE_READ(*addr);
+	}
+
+	check(_metadata, self, addr, MADV_HARD_ANON_HUGETLB, ret);
+
+	cleanup(_metadata, self, addr);
+
+	ASSERT_EQ(munmap(addr, alloc_size), 0);
+}
+
 static int prepare_file(const char *fname, unsigned long size)
 {
 	int fd;
-- 
2.55.0.rc0.799.gd6f94ed593-goog

Re: [PATCH v6 0/5] Only free healthy pages in high-order has_hwpoisoned folio

[Andrew Morton]

On Sun,  5 Jul 2026 18:07:09 +0000 Jiaqi Yan <jiaqiyan@google.com> wrote:

> At the end of dissolve_free_hugetlb_folio(), a free HugeTLB
> folio becomes non-HugeTLB and is released to buddy allocator
> as a high-order folio, e.g. a folio that contains 262144 pages
> if the folio was a 1G HugeTLB hugepage.
> 
> ...
> 
> Introduce free_has_hwpoisoned() to only free the healthy pages
> and exclude the HWPoison ones in the high-order folio.
> free_has_hwpoisoned() happens at the end of free_pages_prepare(),
> which already deals with both decomposing the original compound
> page, updating page metadata like alloc tag and page owner.
> It is also only applied when PG_has_hwpoisoned indicates folio
> contains certain HWPoison page(s) for performance reason.
> Its idea is to iterate through the sub-pages of the folio to
> identify contiguous ranges of healthy pages. Instead of freeing
> pages one by one, free_has_hwpoisoned() then re-use
> free_prepared_contig_range() [11] to decompose healthy ranges into
> the largest possible chunks of different orders. Every chunk is
> freed via __free_frozen_pages().

Thanks.  I'll await further reviewer input before taking any action
with this series.

AI review flags several possible issues, some of them pre-existing:

	https://sashiko.dev/#/patchset/20260705180714.3708947-1-jiaqiyan@google.com

Re: [PATCH v6 0/5] Only free healthy pages in high-order has_hwpoisoned folio

[David Hildenbrand (Arm)]

On 7/5/26 20:50, Andrew Morton wrote:
> On Sun,  5 Jul 2026 18:07:09 +0000 Jiaqi Yan <jiaqiyan@google.com> wrote:
> 
>> At the end of dissolve_free_hugetlb_folio(), a free HugeTLB
>> folio becomes non-HugeTLB and is released to buddy allocator
>> as a high-order folio, e.g. a folio that contains 262144 pages
>> if the folio was a 1G HugeTLB hugepage.
>>
>> ...
>>
>> Introduce free_has_hwpoisoned() to only free the healthy pages
>> and exclude the HWPoison ones in the high-order folio.
>> free_has_hwpoisoned() happens at the end of free_pages_prepare(),
>> which already deals with both decomposing the original compound
>> page, updating page metadata like alloc tag and page owner.
>> It is also only applied when PG_has_hwpoisoned indicates folio
>> contains certain HWPoison page(s) for performance reason.
>> Its idea is to iterate through the sub-pages of the folio to
>> identify contiguous ranges of healthy pages. Instead of freeing
>> pages one by one, free_has_hwpoisoned() then re-use
>> free_prepared_contig_range() [11] to decompose healthy ranges into
>> the largest possible chunks of different orders. Every chunk is
>> freed via __free_frozen_pages().
> 
> Thanks.  I'll await further reviewer input before taking any action
> with this series.

FWIW, I want Vlastimil to ack this before this goes upstream.

-- 
Cheers,

David