[PATCH v7 00/13] Use generic_file_read_iter() in hugetlbfs

[PATCH v7 00/13] Use generic_file_read_iter() in hugetlbfs

[Matthew Wilcox (Oracle)]

This set of patches are separated out from Jane's earlier series.
https://lore.kernel.org/linux-mm/20260617172534.1740152-1-jane.chu@oracle.com/

We need three things to use filemap_read_iter() instead of a hugetlbfs
specific read_iter: hwpoison handling, treating gaps in the pagecache as
holes, and having hugetlb set the folio size in the mapping.  hwopison
handling turned out to need a lot of prep work; the other two things
are fairly straightforward.

Sashiko complains that the implementation of AS_AUTHORITATIVE is
incomplete, but hugetlbfs doesn't use any of that functionality.
We'll add it when we need it, either when hugetlbfs uses it, or when we
convert shmem to use filemap.

v6 here:
https://lore.kernel.org/linux-mm/20260727181310.2671972-1-willy@infradead.org/

Changes from v6:
 - Add folio_clear_hugetlb() helper in hugetlb.c to make sure we move
   the hwpoison flag to individual pages before clearing the hugetlb
   page type.
 - Add missing spin_unlock in an unpoison_memory() error path.
 - Add some R-b tags

Jane Chu (2):
  filemap: Add hwpoison handling to filemap_read()
  hugetlb: replace hugetlbfs_read_iter() with generic_file_read_iter()

Matthew Wilcox (Oracle) (11):
  memory-failure: Fix hardware poison check in unpoison_memory() again
  mm: Rename folio_contain_hwpoison_page() to folio_has_hwpoison_page()
  hugetlb: Mark some function arguments as const
  guest_memfd: Use folio_has_hwpoisoned_page()
  hugetlb: Move poison to pages before clearing hugetlb page type
  hugetlb: Use the has_hwpoisoned flag
  mm: Remove locking mf_mutex in is_raw_hwpoison_page_in_hugepage()
  mm: Check individual hugetlb pages for poison
  filemap: Remove checks in mapping_set_folio_order_range()
  hugetlb: Set mapping folio order
  filemap: Add support for authoritative mappings

 fs/Kconfig                 |   2 +-
 fs/hugetlbfs/inode.c       | 123 +++--------------------
 include/linux/hugetlb.h    |  24 ++---
 include/linux/mm_types.h   |   4 +-
 include/linux/page-flags.h |  63 ++++++++++--
 include/linux/pagemap.h    |  45 +++++----
 mm/Kconfig                 |   6 +-
 mm/filemap.c               |  51 +++++++++-
 mm/huge_memory.c           |   2 +-
 mm/hugetlb.c               |  41 ++++----
 mm/memory-failure.c        | 197 +++++++++++++++++++++++++------------
 mm/memory_hotplug.c        |   2 +-
 mm/rmap.c                  |  43 +++++---
 mm/shmem.c                 |   2 +-
 mm/vmscan.c                |   2 +-
 virt/kvm/guest_memfd.c     |   2 +-
 16 files changed, 346 insertions(+), 263 deletions(-)

-- 
2.47.3

[PATCH v7 01/13] memory-failure: Fix hardware poison check in unpoison_memory() again

[Matthew Wilcox (Oracle)]

The earlier patch (6c54312f9689) that attempted to fix unpoison_memory()
was incorrect for hugetlb folios.  Before a6fddef49eef, we checked
the head page for poison (which was correct for hugetlb and incorrect
for THP).  We are currently incapable of unpoisoning pages (other than
the first page) in a hugetlb folio.

Use is_page_hwpoison() which handles hugetlb pages sufficiently well for
this purpose.  This is racy as we don't have a reference on the folio at
this point, but fixing that properly requires deeper surgery and this
is a CAP_SYS_ADMIN path only so this will do for the moment and can be
easily backported.  It's no worse than the situation before a6fddef49eef.

The other bug in a6fddef49eef is that we currently clear the HWPoison
flag on the precise page, which is wrong for hugetlb.  Fix that too.

Fixes: a6fddef49eef ("mm/memory-failure: convert unpoison_memory() to folios")
Cc: stable@vger.kernel.org
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/memory-failure.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 51508a55c405..944e6e1d4971 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2695,8 +2695,8 @@ int unpoison_memory(unsigned long pfn)
 		goto unlock_mutex;
 	}
 
-	if (!PageHWPoison(p)) {
-		unpoison_pr_info("%#lx: page was already unpoisoned\n",
+	if (!is_page_hwpoison(p)) {
+		unpoison_pr_info("%#lx: page is not poisoned\n",
 				 pfn, &unpoison_rs);
 		goto unlock_mutex;
 	}
@@ -2748,6 +2748,7 @@ int unpoison_memory(unsigned long pfn)
 				folio_put(folio);
 				goto unlock_mutex;
 			}
+			p = &folio->page;
 		}
 
 		folio_put(folio);
-- 
2.47.3

Re: [PATCH v7 01/13] memory-failure: Fix hardware poison check in unpoison_memory() again

[Gregory Price]

On Tue, Jul 28, 2026 at 09:43:53PM +0100, Matthew Wilcox (Oracle) wrote:
> The earlier patch (6c54312f9689) that attempted to fix unpoison_memory()
> was incorrect for hugetlb folios.  Before a6fddef49eef, we checked
> the head page for poison (which was correct for hugetlb and incorrect
> for THP).  We are currently incapable of unpoisoning pages (other than
> the first page) in a hugetlb folio.
> 
> Use is_page_hwpoison() which handles hugetlb pages sufficiently well for
> this purpose.  This is racy as we don't have a reference on the folio at
> this point, but fixing that properly requires deeper surgery and this
> is a CAP_SYS_ADMIN path only so this will do for the moment and can be
> easily backported.  It's no worse than the situation before a6fddef49eef.
> 
> The other bug in a6fddef49eef is that we currently clear the HWPoison
> flag on the precise page, which is wrong for hugetlb.  Fix that too.
> 
> Fixes: a6fddef49eef ("mm/memory-failure: convert unpoison_memory() to folios")
> Cc: stable@vger.kernel.org
> Cc: Miaohe Lin <linmiaohe@huawei.com>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Just trying to wrap my head around the state before/after, assuming
the following is correct then LGTM:

prior:
   pfn_to_online_page(pfn) -> p = precise page
   PageHWPoison(page)      -> checks precise page. Poison for hugetlb
                              is only set only on the head, so bug.
after:
   is_page_hwpoison(page)  -> checks precise page AND head (if hugetlb)
   p = folio->page         -> now TestClearPageHWPoison() explicitly
                              clears the head page poison if hugetlb

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

Re: [PATCH v7 01/13] memory-failure: Fix hardware poison check in unpoison_memory() again

[Matthew Wilcox]

On Tue, Jul 28, 2026 at 08:39:29PM -0400, Gregory Price wrote:
> On Tue, Jul 28, 2026 at 09:43:53PM +0100, Matthew Wilcox (Oracle) wrote:
> > The earlier patch (6c54312f9689) that attempted to fix unpoison_memory()
> > was incorrect for hugetlb folios.  Before a6fddef49eef, we checked
> > the head page for poison (which was correct for hugetlb and incorrect
> > for THP).  We are currently incapable of unpoisoning pages (other than
> > the first page) in a hugetlb folio.
> > 
> > Use is_page_hwpoison() which handles hugetlb pages sufficiently well for
> > this purpose.  This is racy as we don't have a reference on the folio at
> > this point, but fixing that properly requires deeper surgery and this
> > is a CAP_SYS_ADMIN path only so this will do for the moment and can be
> > easily backported.  It's no worse than the situation before a6fddef49eef.
> > 
> > The other bug in a6fddef49eef is that we currently clear the HWPoison
> > flag on the precise page, which is wrong for hugetlb.  Fix that too.
> > 
> > Fixes: a6fddef49eef ("mm/memory-failure: convert unpoison_memory() to folios")
> > Cc: stable@vger.kernel.org
> > Cc: Miaohe Lin <linmiaohe@huawei.com>
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> Just trying to wrap my head around the state before/after, assuming
> the following is correct then LGTM:
> 
> prior:
>    pfn_to_online_page(pfn) -> p = precise page
>    PageHWPoison(page)      -> checks precise page. Poison for hugetlb
>                               is only set only on the head, so bug.
> after:
>    is_page_hwpoison(page)  -> checks precise page AND head (if hugetlb)
>    p = folio->page         -> now TestClearPageHWPoison() explicitly
>                               clears the head page poison if hugetlb

Exactly.  That was how it worked before a6fddef49eef; it used to do
p = compound_head(p) (which wasn't great _either_ but had different
problems ...)

The careful reader will observe that injecting two memory failures
into the same hugetlb causes ... problems.  That's true before and after
this patch, so it's no longer a regression.

> Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>
> 

[PATCH v7 02/13] mm: Rename folio_contain_hwpoison_page() to folio_has_hwpoison_page()

[Matthew Wilcox (Oracle)]

This is a better name for this predicate.  Also make the argument const
to allow other callers to be made const.  No functional change.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Usama Arif <usama.arif@linux.dev>
Reviewed-by: Gregory Price <gourry@gourry.net>
---
 include/linux/page-flags.h | 4 ++--
 mm/huge_memory.c           | 2 +-
 mm/memory_hotplug.c        | 2 +-
 mm/shmem.c                 | 2 +-
 mm/vmscan.c                | 2 +-
 5 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 7223f6f4e2b4..4185a03a45cf 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1083,10 +1083,10 @@ static inline bool is_page_hwpoison(const struct page *page)
 	return folio_test_hugetlb(folio) && PageHWPoison(&folio->page);
 }
 
-static inline bool folio_contain_hwpoisoned_page(struct folio *folio)
+static inline bool folio_has_hwpoisoned_page(const struct folio *folio)
 {
 	return folio_test_hwpoison(folio) ||
-	    (folio_test_large(folio) && folio_test_has_hwpoisoned(folio));
+	       (folio_test_large(folio) && folio_test_has_hwpoisoned(folio));
 }
 
 bool is_free_buddy_page(const struct page *page);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2bccb0a53a0a..353340309107 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4413,7 +4413,7 @@ static bool thp_underused(struct folio *folio)
 	if (khugepaged_max_ptes_none == HPAGE_PMD_NR - 1)
 		return false;
 
-	if (folio_contain_hwpoisoned_page(folio))
+	if (folio_has_hwpoisoned_page(folio))
 		return false;
 
 	for (i = 0; i < folio_nr_pages(folio); i++) {
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 7ac19fab2263..33007e8e546a 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1813,7 +1813,7 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 		if (folio_test_large(folio))
 			pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1;
 
-		if (folio_contain_hwpoisoned_page(folio)) {
+		if (folio_has_hwpoisoned_page(folio)) {
 			/*
 			 * unmap_poisoned_folio() cannot handle large folios
 			 * in all cases yet.
diff --git a/mm/shmem.c b/mm/shmem.c
index b51f83c970bb..492c9bef3620 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3240,7 +3240,7 @@ shmem_write_begin(const struct kiocb *iocb, struct address_space *mapping,
 	if (ret)
 		return ret;
 
-	if (folio_contain_hwpoisoned_page(folio)) {
+	if (folio_has_hwpoisoned_page(folio)) {
 		folio_unlock(folio);
 		folio_put(folio);
 		return -EIO;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 35c3bb15ae96..70e54ace0e74 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1086,7 +1086,7 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 		if (!folio_trylock(folio))
 			goto keep;
 
-		if (folio_contain_hwpoisoned_page(folio)) {
+		if (folio_has_hwpoisoned_page(folio)) {
 			/*
 			 * unmap_poisoned_folio() can't handle large
 			 * folio, just skip it. memory_failure() will
-- 
2.47.3

[PATCH v7 03/13] hugetlb: Mark some function arguments as const

[Matthew Wilcox (Oracle)]

These functions do not modify their folio argument, so we can mark them
as being const which will allow for some minor optimisations and let us
mark other function arguments as being const in the future.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Usama Arif <usama.arif@linux.dev>
Reviewed-by: Gregory Price <gourry@gourry.net>
---
 include/linux/hugetlb.h | 19 +++++++++----------
 mm/hugetlb.c            |  2 +-
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 2abaf99321e9..18661a7cdb37 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -165,7 +165,7 @@ bool hugetlbfs_pagecache_present(struct hstate *h,
 				 struct vm_area_struct *vma,
 				 unsigned long address);
 
-struct address_space *hugetlb_folio_mapping_lock_write(struct folio *folio);
+struct address_space *hugetlb_folio_mapping_lock_write(const struct folio *folio);
 
 extern int movable_gigantic_pages __read_mostly;
 extern int sysctl_hugetlb_shm_group __read_mostly;
@@ -292,8 +292,7 @@ static inline unsigned long hugetlb_total_pages(void)
 	return 0;
 }
 
-static inline struct address_space *hugetlb_folio_mapping_lock_write(
-							struct folio *folio)
+static inline struct address_space *hugetlb_folio_mapping_lock_write(const struct folio *folio)
 {
 	return NULL;
 }
@@ -595,8 +594,8 @@ enum hugetlb_page_flags {
 #ifdef CONFIG_HUGETLB_PAGE
 #define TESTHPAGEFLAG(uname, flname)				\
 static __always_inline						\
-bool folio_test_hugetlb_##flname(struct folio *folio)		\
-	{	void *private = &folio->private;		\
+bool folio_test_hugetlb_##flname(const struct folio *folio)	\
+	{	const void *private = &folio->private;		\
 		return test_bit(HPG_##flname, private);		\
 	}
 
@@ -616,7 +615,7 @@ void folio_clear_hugetlb_##flname(struct folio *folio)		\
 #else
 #define TESTHPAGEFLAG(uname, flname)				\
 static inline bool						\
-folio_test_hugetlb_##flname(struct folio *folio)		\
+folio_test_hugetlb_##flname(const struct folio *folio)		\
 	{ return 0; }
 
 #define SETHPAGEFLAG(uname, flname)				\
@@ -727,7 +726,7 @@ static inline struct hugepage_subpool *subpool_inode(struct inode *inode)
 	return HUGETLBFS_SB(inode->i_sb)->spool;
 }
 
-static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio)
+static inline struct hugepage_subpool *hugetlb_folio_subpool(const struct folio *folio)
 {
 	return folio->_hugetlb_subpool;
 }
@@ -857,7 +856,7 @@ static inline bool arch_has_huge_bootmem_alloc(void)
 }
 #endif
 
-static inline struct hstate *folio_hstate(struct folio *folio)
+static inline struct hstate *folio_hstate(const struct folio *folio)
 {
 	VM_BUG_ON_FOLIO(!folio_test_hugetlb(folio), folio);
 	return size_to_hstate(folio_size(folio));
@@ -1088,7 +1087,7 @@ static inline unsigned long huge_page_mask_align(struct file *file)
 	return 0;
 }
 
-static inline struct hugepage_subpool *hugetlb_folio_subpool(struct folio *folio)
+static inline struct hugepage_subpool *hugetlb_folio_subpool(const struct folio *folio)
 {
 	return NULL;
 }
@@ -1157,7 +1156,7 @@ static inline struct hstate *hstate_vma(struct vm_area_struct *vma)
 	return NULL;
 }
 
-static inline struct hstate *folio_hstate(struct folio *folio)
+static inline struct hstate *folio_hstate(const struct folio *folio)
 {
 	return NULL;
 }
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 571212b80835..cc8d98399913 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1775,7 +1775,7 @@ void init_new_hugetlb_folio(struct folio *folio)
  * stable.  Due to locking order, we can only trylock_write.  If we can
  * not get the lock, simply return NULL to caller.
  */
-struct address_space *hugetlb_folio_mapping_lock_write(struct folio *folio)
+struct address_space *hugetlb_folio_mapping_lock_write(const struct folio *folio)
 {
 	struct address_space *mapping = folio_mapping(folio);
 
-- 
2.47.3

[PATCH v7 04/13] guest_memfd: Use folio_has_hwpoisoned_page()

[Matthew Wilcox (Oracle)]

folio_test_hwpoison() only works on hugetlb folios today and will give
the wrong answer for other large folios.  folio_has_hwpoisoned_page()
works on both.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
---
 virt/kvm/guest_memfd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index db57c5766ab6..94eedcc7f1a9 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -774,7 +774,7 @@ static struct folio *__kvm_gmem_get_pfn(struct file *file,
 	if (IS_ERR(folio))
 		return folio;
 
-	if (folio_test_hwpoison(folio)) {
+	if (folio_has_hwpoisoned_page(folio)) {
 		folio_unlock(folio);
 		folio_put(folio);
 		return ERR_PTR(-EHWPOISON);
-- 
2.47.3

[PATCH v7 05/13] hugetlb: Move poison to pages before clearing hugetlb page type

[Matthew Wilcox (Oracle)]

For is_page_hwpoison() to be reliable, we need to set the hwpoison
flag on each page before clearing the hugetlb flag.  Introduce
folio_clear_hugetlb() to make this easier.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/hugetlb.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index cc8d98399913..47403d02be88 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1381,6 +1381,18 @@ static struct folio *alloc_gigantic_frozen_folio(int order, gfp_t gfp_mask, int
 }
 #endif
 
+static void folio_clear_hugetlb(struct folio *folio)
+{
+	/*
+	 * Move HWPoison flag to each error page
+	 * which makes any healthy pages reusable.
+	 */
+	if (unlikely(folio_test_hwpoison(folio)))
+		folio_clear_hugetlb_hwpoison(folio);
+
+	__folio_clear_hugetlb(folio);
+}
+
 /*
  * Remove hugetlb folio from lists.
  * If vmemmap exists for the folio, clear the hugetlb flag so that the
@@ -1419,7 +1431,7 @@ void remove_hugetlb_folio(struct hstate *h, struct folio *folio,
 	 * to tail struct pages.
 	 */
 	if (!folio_test_hugetlb_vmemmap_optimized(folio))
-		__folio_clear_hugetlb(folio);
+		folio_clear_hugetlb(folio);
 
 	h->nr_huge_pages--;
 	h->nr_huge_pages_node[nid]--;
@@ -1493,17 +1505,10 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
 	 */
 	if (folio_test_hugetlb(folio)) {
 		spin_lock_irq(&hugetlb_lock);
-		__folio_clear_hugetlb(folio);
+		folio_clear_hugetlb(folio);
 		spin_unlock_irq(&hugetlb_lock);
 	}
 
-	/*
-	 * Move PageHWPoison flag from head page to the raw error pages,
-	 * which makes any healthy subpages reusable.
-	 */
-	if (unlikely(folio_test_hwpoison(folio)))
-		folio_clear_hugetlb_hwpoison(folio);
-
 	VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
 	if (folio_test_hugetlb_cma(folio))
 		hugetlb_cma_free_frozen_folio(folio);
@@ -1595,7 +1600,7 @@ static void bulk_vmemmap_restore_error(struct hstate *h,
 		list_for_each_entry_safe(folio, t_folio, non_hvo_folios, lru) {
 			list_del(&folio->lru);
 			spin_lock_irq(&hugetlb_lock);
-			__folio_clear_hugetlb(folio);
+			folio_clear_hugetlb(folio);
 			spin_unlock_irq(&hugetlb_lock);
 			update_and_free_hugetlb_folio(h, folio, false);
 			cond_resched();
@@ -1620,7 +1625,7 @@ static void bulk_vmemmap_restore_error(struct hstate *h,
 			} else {
 				list_del(&folio->lru);
 				spin_lock_irq(&hugetlb_lock);
-				__folio_clear_hugetlb(folio);
+				folio_clear_hugetlb(folio);
 				spin_unlock_irq(&hugetlb_lock);
 				update_and_free_hugetlb_folio(h, folio, false);
 				cond_resched();
@@ -1653,14 +1658,14 @@ static void update_and_free_pages_bulk(struct hstate *h,
 	 * should only be pages on the non_hvo_folios list.
 	 * Do note that the non_hvo_folios list could be empty.
 	 * Without HVO enabled, ret will be 0 and there is no need to call
-	 * __folio_clear_hugetlb as this was done previously.
+	 * folio_clear_hugetlb as this was done previously.
 	 */
 	VM_WARN_ON(!list_empty(folio_list));
 	VM_WARN_ON(ret < 0);
 	if (!list_empty(&non_hvo_folios) && ret) {
 		spin_lock_irq(&hugetlb_lock);
 		list_for_each_entry(folio, &non_hvo_folios, lru)
-			__folio_clear_hugetlb(folio);
+			folio_clear_hugetlb(folio);
 		spin_unlock_irq(&hugetlb_lock);
 	}
 
-- 
2.47.3

Re: [PATCH v7 05/13] hugetlb: Move poison to pages before clearing hugetlb page type

[Gregory Price]

On Tue, Jul 28, 2026 at 09:43:57PM +0100, Matthew Wilcox (Oracle) wrote:
> For is_page_hwpoison() to be reliable, we need to set the hwpoison
> flag on each page before clearing the hugetlb flag.  Introduce
> folio_clear_hugetlb() to make this easier.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>

[PATCH v7 06/13] hugetlb: Use the has_hwpoisoned flag

[Matthew Wilcox (Oracle)]

Other large folios use the has_hwpoisoned flag.  Convert hugetlb to match.
This will help us use the per-page hwpoison flag in the future.

Also introduce a folio_test_huge_poison().  This has exactly the same
meaning as folio_test_has_hwpoisoned() but can be used when we don't have
a reference to the folio containing the page.  folio_test_has_hwpoisoned()
can race with folio splitting / reallocation and trip the assertions
in const_folio_flags().

This closes a gap where a page in a previously-poisoned hugetlb folio
could be observed to not have the hwpoison bit set.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/Kconfig                 |  2 +-
 fs/hugetlbfs/inode.c       |  2 +-
 include/linux/page-flags.h | 46 ++++++++++++++++++++++-----
 mm/Kconfig                 |  6 +++-
 mm/hugetlb.c               | 10 +++---
 mm/memory-failure.c        | 64 ++++++++++++++++++++++++++++----------
 mm/rmap.c                  | 43 +++++++++++++++----------
 7 files changed, 124 insertions(+), 49 deletions(-)

diff --git a/fs/Kconfig b/fs/Kconfig
index cf6ae64776e6..eddac4ed214b 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -272,7 +272,7 @@ endif # HUGETLBFS
 
 config HUGETLB_PAGE
 	def_bool HUGETLBFS
-	select XARRAY_MULTI
+	select LARGE_FOLIO
 
 config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	def_bool HUGETLB_PAGE
diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 216e1a0dd0b2..fbac554886c3 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -258,7 +258,7 @@ static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
 		} else {
 			folio_unlock(folio);
 
-			if (!folio_test_hwpoison(folio))
+			if (!folio_test_has_hwpoisoned(folio))
 				want = nr;
 			else {
 				/*
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 4185a03a45cf..4fab3fbfd430 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -893,14 +893,19 @@ static inline int PageTransCompound(const struct page *page)
 TESTPAGEFLAG_FALSE(TransCompound, transcompound)
 #endif
 
-#if defined(CONFIG_MEMORY_FAILURE) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
+#if defined(CONFIG_MEMORY_FAILURE) && defined(CONFIG_LARGE_FOLIO)
 /*
- * PageHasHWPoisoned indicates that at least one subpage is hwpoisoned in the
- * compound page.
+ * folio_has_hwpoisoned indicates that at least one page is hwpoisoned in the
+ * folio.  That page will usually also have the HWPoison flag set, but this
+ * is not possible for folios which have HVO (see memory-failure for the
+ * scheme used in that case).  You probably don't want to call this directly;
+ * use folio_has_hwpoisoned_page() instead.
  *
  * This flag is set by hwpoison handler.  Cleared by THP split or free page.
  */
 FOLIO_FLAG(has_hwpoisoned, FOLIO_SECOND_PAGE)
+FOLIO_TEST_SET_FLAG(has_hwpoisoned, FOLIO_SECOND_PAGE)
+FOLIO_TEST_CLEAR_FLAG(has_hwpoisoned, FOLIO_SECOND_PAGE)
 #else
 FOLIO_FLAG_FALSE(has_hwpoisoned)
 #endif
@@ -1041,8 +1046,29 @@ PAGE_TYPE_OPS(Slab, slab, slab)
 
 #ifdef CONFIG_HUGETLB_PAGE
 FOLIO_TYPE_OPS(hugetlb, hugetlb)
+
+#ifdef CONFIG_MEMORY_FAILURE
+static inline bool folio_test_huge_poison(const struct folio *folio)
+{
+	return (READ_ONCE(folio->page.page_type) >> 23) ==
+		((PGTY_hugetlb << 1) | 1);
+}
+
+static inline void folio_set_huge_poison(struct folio *folio)
+{
+	folio->page.page_type |= (1 << 23);
+}
+
+static inline void folio_clear_huge_poison(struct folio *folio)
+{
+	folio->page.page_type &= ~(1 << 23);
+}
+#else
+FOLIO_TEST_FLAG_FALSE(huge_poison)
+#endif
 #else
 FOLIO_TEST_FLAG_FALSE(hugetlb)
+FOLIO_TEST_FLAG_FALSE(huge_poison)
 #endif
 
 PAGE_TYPE_OPS(Zsmalloc, zsmalloc, zsmalloc)
@@ -1069,9 +1095,10 @@ static inline bool PageHuge(const struct page *page)
 }
 
 /*
- * Check if a page is currently marked HWPoisoned. Note that this check is
- * best effort only and inherently racy: there is no way to synchronize with
- * failing hardware.
+ * Check if a page is currently marked HWPoisoned.  This check is best
+ * effort only and inherently racy: there is no way to synchronize with
+ * failing hardware.  The caller may not have a refcount on the folio
+ * containing the page, so we must be careful to not trip any assertions.
  */
 static inline bool is_page_hwpoison(const struct page *page)
 {
@@ -1080,12 +1107,15 @@ static inline bool is_page_hwpoison(const struct page *page)
 	if (PageHWPoison(page))
 		return true;
 	folio = page_folio(page);
-	return folio_test_hugetlb(folio) && PageHWPoison(&folio->page);
+	if (folio_test_huge_poison(folio))
+		return true;
+	/* In case we raced with hugetlb transferring flags */
+	return PageHWPoison(page);
 }
 
 static inline bool folio_has_hwpoisoned_page(const struct folio *folio)
 {
-	return folio_test_hwpoison(folio) ||
+	return PageHWPoison(&folio->page) ||
 	       (folio_test_large(folio) && folio_test_has_hwpoisoned(folio));
 }
 
diff --git a/mm/Kconfig b/mm/Kconfig
index 9e0ca4824905..e666dd14ca0c 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -843,11 +843,15 @@ config PERSISTENT_HUGE_ZERO_FOLIO
 config MM_ID
 	def_bool n
 
+config LARGE_FOLIO
+	def_bool n
+	select XARRAY_MULTI
+
 menuconfig TRANSPARENT_HUGEPAGE
 	bool "Transparent Hugepage Support"
 	depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE && !PREEMPT_RT
 	select COMPACTION
-	select XARRAY_MULTI
+	select LARGE_FOLIO
 	select MM_ID
 	help
 	  Transparent Hugepages allows the kernel to use huge pages and
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 47403d02be88..40ae967b9ecc 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1255,7 +1255,7 @@ static struct folio *dequeue_hugetlb_folio_node_exact(struct hstate *h,
 		if (pin && !folio_is_longterm_pinnable(folio))
 			continue;
 
-		if (folio_test_hwpoison(folio))
+		if (folio_test_has_hwpoisoned(folio))
 			continue;
 
 		if (is_migrate_isolate_page(&folio->page))
@@ -1387,7 +1387,7 @@ static void folio_clear_hugetlb(struct folio *folio)
 	 * Move HWPoison flag to each error page
 	 * which makes any healthy pages reusable.
 	 */
-	if (unlikely(folio_test_hwpoison(folio)))
+	if (unlikely(folio_test_has_hwpoisoned(folio)))
 		folio_clear_hugetlb_hwpoison(folio);
 
 	__folio_clear_hugetlb(folio);
@@ -4003,7 +4003,7 @@ long demote_pool_huge_page(struct hstate *src, nodemask_t *nodes_allowed,
 		struct folio *folio, *next;
 
 		list_for_each_entry_safe(folio, next, &src->hugepage_freelists[node], lru) {
-			if (folio_test_hwpoison(folio))
+			if (folio_test_has_hwpoisoned(folio))
 				continue;
 
 			remove_hugetlb_folio(src, folio, false);
@@ -5814,7 +5814,7 @@ static vm_fault_t hugetlb_no_page(struct address_space *mapping,
 		 * don't have hwpoisoned swap entry for errored virtual address.
 		 * So we need to block hugepage fault by PG_hwpoison bit check.
 		 */
-		if (unlikely(folio_test_hwpoison(folio))) {
+		if (unlikely(folio_test_has_hwpoisoned(folio))) {
 			ret = VM_FAULT_HWPOISON_LARGE |
 				VM_FAULT_SET_HINDEX(hstate_index(h));
 			goto backout_unlocked;
@@ -6323,7 +6323,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
 	ptl = huge_pte_lock(h, dst_mm, dst_pte);
 
 	ret = -EIO;
-	if (folio_test_hwpoison(folio))
+	if (folio_test_has_hwpoisoned(folio))
 		goto out_release_unlock;
 
 	ret = -EEXIST;
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 944e6e1d4971..fda6698e5e0f 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1829,7 +1829,7 @@ bool is_raw_hwpoison_page_in_hugepage(struct page *page)
 	struct folio *folio = page_folio(page);
 	bool ret = false;
 
-	if (!folio_test_hwpoison(folio))
+	if (!folio_test_has_hwpoisoned(folio))
 		return false;
 
 	if (!folio_test_hugetlb(folio))
@@ -1881,6 +1881,24 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
 #define	MF_HUGETLB_FOLIO_PRE_POISONED	3	/* folio already poisoned */
 #define	MF_HUGETLB_PAGE_PRE_POISONED	4	/* exact page already poisoned */
 #define	MF_HUGETLB_RETRY		5	/* hugepage is busy, retry */
+
+static inline int hugetlb_set_poison(struct folio *folio)
+{
+	if (folio_test_set_has_hwpoisoned(folio))
+		return MF_HUGETLB_FOLIO_PRE_POISONED;
+	folio_set_huge_poison(folio);
+	return 0;
+}
+
+static inline int hugetlb_clear_poison(struct folio *folio)
+{
+	if (!folio_test_has_hwpoisoned(folio))
+		return -EBUSY;
+	folio_clear_huge_poison(folio);
+	folio_clear_has_hwpoisoned(folio);
+	return 0;
+}
+
 /*
  * Set hugetlb folio as hwpoisoned, update folio private raw hwpoison list
  * to keep track of the poisoned pages.
@@ -1890,12 +1908,12 @@ static int hugetlb_update_hwpoison(struct folio *folio, struct page *page)
 	struct llist_head *head;
 	struct raw_hwp_page *raw_hwp;
 	struct raw_hwp_page *p;
-	int ret = folio_test_set_hwpoison(folio) ? MF_HUGETLB_FOLIO_PRE_POISONED : 0;
+	int ret = hugetlb_set_poison(folio);
 
 	/*
 	 * Once the hwpoison hugepage has lost reliable raw error info,
-	 * there is little meaning to keep additional error info precisely,
-	 * so skip to add additional raw error info.
+	 * there is no point in keeping additional error info precisely,
+	 * so skip adding additional raw error info.
 	 */
 	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
 		return MF_HUGETLB_FOLIO_PRE_POISONED;
@@ -1950,8 +1968,8 @@ void folio_clear_hugetlb_hwpoison(struct folio *folio)
 		return;
 	if (folio_test_hugetlb_vmemmap_optimized(folio))
 		return;
-	folio_clear_hwpoison(folio);
 	folio_free_raw_hwp(folio, true);
+	folio_clear_has_hwpoisoned(folio);
 }
 
 static int get_huge_page_for_hwpoison(unsigned long pfn, int flags,
@@ -2104,6 +2122,11 @@ static inline unsigned long folio_free_raw_hwp(struct folio *folio, bool flag)
 {
 	return 0;
 }
+
+static inline int hugetlb_clear_poison(struct folio *folio)
+{
+	return 0;
+}
 #endif	/* CONFIG_HUGETLB_PAGE */
 
 /* Drop the extra refcount in case we come from madvise() */
@@ -2725,13 +2748,19 @@ int unpoison_memory(unsigned long pfn)
 
 	ghp = get_hwpoison_page(p, MF_UNPOISON);
 	if (!ghp) {
+		spin_lock_irq(&hugetlb_lock);
 		if (folio_test_hugetlb(folio)) {
 			huge = true;
 			count = folio_free_raw_hwp(folio, false);
-			if (count == 0)
+			if (count == 0) {
+				spin_unlock_irq(&hugetlb_lock);
 				goto unlock_mutex;
+			}
+			ret = hugetlb_clear_poison(folio);
+		} else {
+			ret = TestClearPageHWPoison(p) ? 0 : -EBUSY;
 		}
-		ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
+		spin_unlock_irq(&hugetlb_lock);
 	} else if (ghp < 0) {
 		if (ghp == -EHWPOISON) {
 			ret = put_page_back_buddy(p) ? 0 : -EBUSY;
@@ -2740,17 +2769,18 @@ int unpoison_memory(unsigned long pfn)
 			unpoison_pr_info("%#lx: failed to grab page\n",
 					 pfn, &unpoison_rs);
 		}
-	} else {
-		if (folio_test_hugetlb(folio)) {
-			huge = true;
-			count = folio_free_raw_hwp(folio, false);
-			if (count == 0) {
-				folio_put(folio);
-				goto unlock_mutex;
-			}
-			p = &folio->page;
+	} else if (folio_test_hugetlb(folio)) {
+		huge = true;
+		count = folio_free_raw_hwp(folio, false);
+		if (count == 0) {
+			folio_put(folio);
+			goto unlock_mutex;
 		}
-
+		ret = hugetlb_clear_poison(folio);
+		folio_put(folio);
+		if (!ret)
+			folio_put(folio);
+	} else {
 		folio_put(folio);
 		if (TestClearPageHWPoison(p)) {
 			folio_put(folio);
diff --git a/mm/rmap.c b/mm/rmap.c
index 1c77d5dc06e9..fd19a0bfbfe7 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1978,6 +1978,22 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio,
 				     FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY);
 }
 
+/*
+ * Since we cannot split a hugetlb folio, we want to insert a poison
+ * entry into the page table for the whole folio even if only one page
+ * is poisoned.  Otherwise, we've split down to the PTE level and we only
+ * want to poison the precise page
+ */
+static bool ttu_create_hwpoison(const struct folio *folio,
+		const struct page *page, enum ttu_flags flags)
+{
+	if (!(flags & TTU_HWPOISON))
+		return false;
+	if (folio_test_hugetlb(folio))
+		return folio_test_has_hwpoisoned(folio);
+	return PageHWPoison(page);
+}
+
 /*
  * @arg: enum ttu_flags will be passed to this argument
  */
@@ -1993,7 +2009,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 	enum ttu_flags flags = (enum ttu_flags)(long)arg;
 	unsigned long nr_pages = 1, end_addr;
 	unsigned long pfn;
-	unsigned long hsz = 0;
 	int ptes = 0;
 
 	/*
@@ -2023,9 +2038,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 		 */
 		adjust_range_if_pmd_sharing_possible(vma, &range.start,
 						     &range.end);
-
-		/* We need the huge page size for set_huge_pte_at() */
-		hsz = huge_page_size(hstate_vma(vma));
 	}
 	mmu_notifier_invalidate_range_start(&range);
 
@@ -2121,7 +2133,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			 * The try_to_unmap() is only passed a hugetlb page
 			 * in the case where the hugetlb page is poisoned.
 			 */
-			VM_BUG_ON_PAGE(!PageHWPoison(subpage), subpage);
+			VM_BUG_ON_FOLIO(!folio_has_hwpoisoned_page(folio),
+					folio);
 			/*
 			 * huge_pmd_unshare may unmap an entire PMD page.
 			 * There is no way of knowing exactly which PMDs may
@@ -2200,12 +2213,12 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 		/* Update high watermark before we lower rss */
 		update_hiwater_rss(mm);
 
-		if (PageHWPoison(subpage) && (flags & TTU_HWPOISON)) {
+		if (ttu_create_hwpoison(folio, subpage, flags)) {
 			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
 			if (folio_test_hugetlb(folio)) {
 				hugetlb_count_sub(folio_nr_pages(folio), mm);
 				set_huge_pte_at(mm, address, pvmw.pte, pteval,
-						hsz);
+						folio_size(folio));
 			} else {
 				dec_mm_counter(mm, mm_counter(folio));
 				set_pte_at(mm, address, pvmw.pte, pteval);
@@ -2423,7 +2436,6 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 	struct mmu_notifier_range range;
 	enum ttu_flags flags = (enum ttu_flags)(long)arg;
 	unsigned long pfn;
-	unsigned long hsz = 0;
 
 	/*
 	 * When racing against e.g. zap_pte_range() on another cpu,
@@ -2452,9 +2464,6 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 		 */
 		adjust_range_if_pmd_sharing_possible(vma, &range.start,
 						     &range.end);
-
-		/* We need the huge page size for set_huge_pte_at() */
-		hsz = huge_page_size(hstate_vma(vma));
 	}
 	mmu_notifier_invalidate_range_start(&range);
 
@@ -2607,14 +2616,14 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 		/* Update high watermark before we lower rss */
 		update_hiwater_rss(mm);
 
-		if (PageHWPoison(subpage)) {
+		if (ttu_create_hwpoison(folio, subpage, TTU_HWPOISON)) {
 			VM_WARN_ON_FOLIO(folio_is_device_private(folio), folio);
 
 			pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
 			if (folio_test_hugetlb(folio)) {
 				hugetlb_count_sub(folio_nr_pages(folio), mm);
 				set_huge_pte_at(mm, address, pvmw.pte, pteval,
-						hsz);
+						folio_size(folio));
 			} else {
 				dec_mm_counter(mm, mm_counter(folio));
 				set_pte_at(mm, address, pvmw.pte, pteval);
@@ -2644,7 +2653,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 			if (arch_unmap_one(mm, vma, address, pteval) < 0) {
 				if (folio_test_hugetlb(folio))
 					set_huge_pte_at(mm, address, pvmw.pte,
-							pteval, hsz);
+							pteval,
+							folio_size(folio));
 				else
 					set_pte_at(mm, address, pvmw.pte, pteval);
 				ret = false;
@@ -2657,7 +2667,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 				if (anon_exclusive &&
 				    hugetlb_try_share_anon_rmap(folio)) {
 					set_huge_pte_at(mm, address, pvmw.pte,
-							pteval, hsz);
+							pteval,
+							folio_size(folio));
 					ret = false;
 					page_vma_mapped_walk_done(&pvmw);
 					break;
@@ -2703,7 +2714,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 			}
 			if (folio_test_hugetlb(folio))
 				set_huge_pte_at(mm, address, pvmw.pte, swp_pte,
-						hsz);
+						folio_size(folio));
 			else
 				set_pte_at(mm, address, pvmw.pte, swp_pte);
 			trace_set_migration_pte(address, pte_val(swp_pte),
-- 
2.47.3

Re: [PATCH v7 06/13] hugetlb: Use the has_hwpoisoned flag

[Gregory Price]

On Tue, Jul 28, 2026 at 09:43:58PM +0100, Matthew Wilcox (Oracle) wrote:
> +
> +#ifdef CONFIG_MEMORY_FAILURE
> +static inline bool folio_test_huge_poison(const struct folio *folio)
> +{
> +	return (READ_ONCE(folio->page.page_type) >> 23) ==
> +		((PGTY_hugetlb << 1) | 1);
> +}
> +
> +static inline void folio_set_huge_poison(struct folio *folio)
> +{
> +	folio->page.page_type |= (1 << 23);
> +}
> +
> +static inline void folio_clear_huge_poison(struct folio *folio)
> +{
> +	folio->page.page_type &= ~(1 << 23);
> +}
> +#else

Took me a second to realize why this was open-coded instead of using
the generator macros.  The reasoning is buried in this comment:

/*
 * Check if a page is currently marked HWPoisoned.  This check is best
 * effort only and inherently racy: there is no way to synchronize with
 * failing hardware.  The caller may not have a refcount on the folio
 * containing the page, so we must be careful to not trip any assertions.
 */
 static inline bool is_page_hwpoison(const struct page *page)
 ...

which i presume is referring to VM_BUG_ON_FOLIO() in the set/clear in
the macros.  Might be worth just note here if only so no one comes along
and "fixes" this or writes more of these without the same reasoning.

> @@ -2725,13 +2748,19 @@ int unpoison_memory(unsigned long pfn)
>  
>  	ghp = get_hwpoison_page(p, MF_UNPOISON);
>  	if (!ghp) {
> +		spin_lock_irq(&hugetlb_lock);
>  		if (folio_test_hugetlb(folio)) {
>  			huge = true;
>  			count = folio_free_raw_hwp(folio, false);
> -			if (count == 0)
> +			if (count == 0) {
> +				spin_unlock_irq(&hugetlb_lock);
>  				goto unlock_mutex;
> +			}
> +			ret = hugetlb_clear_poison(folio);
> +		} else {
> +			ret = TestClearPageHWPoison(p) ? 0 : -EBUSY;
>  		}
> -		ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
> +		spin_unlock_irq(&hugetlb_lock);

Adding new synchronization here without noting why - it's not
immediately clear what this synchronizes.

Is this just fixing an unrelated bug / should it be a separate patch?

~Gregory

Re: [PATCH v7 06/13] hugetlb: Use the has_hwpoisoned flag

[Matthew Wilcox]

On Tue, Jul 28, 2026 at 09:36:37PM -0400, Gregory Price wrote:
> On Tue, Jul 28, 2026 at 09:43:58PM +0100, Matthew Wilcox (Oracle) wrote:
> > +
> > +#ifdef CONFIG_MEMORY_FAILURE
> > +static inline bool folio_test_huge_poison(const struct folio *folio)
> > +{
> > +	return (READ_ONCE(folio->page.page_type) >> 23) ==
> > +		((PGTY_hugetlb << 1) | 1);
> > +}
> > +
> > +static inline void folio_set_huge_poison(struct folio *folio)
> > +{
> > +	folio->page.page_type |= (1 << 23);
> > +}
> > +
> > +static inline void folio_clear_huge_poison(struct folio *folio)
> > +{
> > +	folio->page.page_type &= ~(1 << 23);
> > +}
> > +#else
> 
> Took me a second to realize why this was open-coded instead of using
> the generator macros.  The reasoning is buried in this comment:

I believe hugetlb is the first user of the low 24 bits of page_type.
As such, there aren't any generator macros yet ... and I'd probably want
there to be at least three before creating any.

> /*
>  * Check if a page is currently marked HWPoisoned.  This check is best
>  * effort only and inherently racy: there is no way to synchronize with
>  * failing hardware.  The caller may not have a refcount on the folio
>  * containing the page, so we must be careful to not trip any assertions.
>  */
>  static inline bool is_page_hwpoison(const struct page *page)
>  ...
> 
> which i presume is referring to VM_BUG_ON_FOLIO() in the set/clear in
> the macros.  Might be worth just note here if only so no one comes along
> and "fixes" this or writes more of these without the same reasoning.

It's even in the test ...

FOLIO_FLAG(has_hwpoisoned, FOLIO_SECOND_PAGE)
#define FOLIO_SECOND_PAGE       1
#define FOLIO_FLAG(name, page)                                          \
FOLIO_TEST_FLAG(name, page)                                             \
#define FOLIO_TEST_FLAG(name, page)                                     \
static __always_inline bool folio_test_##name(const struct folio *folio) \
{ return test_bit(PG_##name, const_folio_flags(folio, page)); }

static const unsigned long *const_folio_flags(const struct folio *folio,
                unsigned n)
{
        const struct page *page = &folio->page;

        VM_BUG_ON_PGFLAGS(page->compound_info & 1, page);
        VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags.f), page);
        return &page[n].flags.f;
}

So there's two asserts that might trip; the first if the folio is freed
then reallocated into a larger folio and the former folio becomes a tail
page.  That's pretty unlikely for a hugetlb folio, but the second is
more likely.  That'll happen just by freeing the folio.

> > @@ -2725,13 +2748,19 @@ int unpoison_memory(unsigned long pfn)
> >  
> >  	ghp = get_hwpoison_page(p, MF_UNPOISON);
> >  	if (!ghp) {
> > +		spin_lock_irq(&hugetlb_lock);
> >  		if (folio_test_hugetlb(folio)) {
> >  			huge = true;
> >  			count = folio_free_raw_hwp(folio, false);
> > -			if (count == 0)
> > +			if (count == 0) {
> > +				spin_unlock_irq(&hugetlb_lock);
> >  				goto unlock_mutex;
> > +			}
> > +			ret = hugetlb_clear_poison(folio);
> > +		} else {
> > +			ret = TestClearPageHWPoison(p) ? 0 : -EBUSY;
> >  		}
> > -		ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
> > +		spin_unlock_irq(&hugetlb_lock);
> 
> Adding new synchronization here without noting why - it's not
> immediately clear what this synchronizes.
> 
> Is this just fixing an unrelated bug / should it be a separate patch?

This prevents a hugetlb folio (which in this arm we don't have a
reference on) from being freed.  I think it ended up in this patch
because Sashiko pointed out the race during review of this patch.
It could probably go in its own patch 

Re: [PATCH v7 06/13] hugetlb: Use the has_hwpoisoned flag

[Matthew Wilcox]

On Wed, Jul 29, 2026 at 03:55:10AM +0100, Matthew Wilcox wrote:
> > > @@ -2725,13 +2748,19 @@ int unpoison_memory(unsigned long pfn)
> > >  
> > >  	ghp = get_hwpoison_page(p, MF_UNPOISON);
> > >  	if (!ghp) {
> > > +		spin_lock_irq(&hugetlb_lock);
> > >  		if (folio_test_hugetlb(folio)) {
> > >  			huge = true;
> > >  			count = folio_free_raw_hwp(folio, false);
> > > -			if (count == 0)
> > > +			if (count == 0) {
> > > +				spin_unlock_irq(&hugetlb_lock);
> > >  				goto unlock_mutex;
> > > +			}
> > > +			ret = hugetlb_clear_poison(folio);
> > > +		} else {
> > > +			ret = TestClearPageHWPoison(p) ? 0 : -EBUSY;
> > >  		}
> > > -		ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
> > > +		spin_unlock_irq(&hugetlb_lock);
> > 
> > Adding new synchronization here without noting why - it's not
> > immediately clear what this synchronizes.
> > 
> > Is this just fixing an unrelated bug / should it be a separate patch?
> 
> This prevents a hugetlb folio (which in this arm we don't have a
> reference on) from being freed.  I think it ended up in this patch
> because Sashiko pointed out the race during review of this patch.
> It could probably go in its own patch 

OK, split out into its own patch.  The 0day bot chewed on it a bit and
came up with a config that enabled MEMORY_FAILURE and disabled HUGETLB
which showed a missing hugetlb_lock symbol.  Here's the new patch:

commit 9df49152f5de
Author: Matthew Wilcox (Oracle) <willy@infradead.org>
Date:   Wed Jul 29 08:41:50 2026 -0400

    memory-failure: Prevent hugetlb freeing during unpoisoning
    
    If we fail to get a reference on the hugetlb folio, then it might be
    freed as we operate on it.  Prevent the freeing and the attendant races
    around manipulation of the raw_hwp list by holding the hugetlb_lock,
    which is also held by the hugetlb code when freeing hugetlb folios.
    
    Fixes: ac5fcde0a96a ("mm, hwpoison: make unpoison aware of raw error info in hwpoisoned hugepage")
    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 2abaf99321e9..50eab2c23299 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -110,6 +110,17 @@ extern struct resv_map *resv_map_alloc(void);
 void resv_map_release(struct kref *ref);
 
 extern spinlock_t hugetlb_lock;
+
+static inline void hugetlb_lock_irq(void)
+{
+	spin_lock_irq(&hugetlb_lock);
+}
+
+static inline void hugetlb_unlock_irq(void)
+{
+	spin_unlock_irq(&hugetlb_lock);
+}
+
 extern int hugetlb_max_hstate __read_mostly;
 #define for_each_hstate(h) \
 	for ((h) = hstates; (h) < &hstates[hugetlb_max_hstate]; (h)++)
@@ -279,6 +290,14 @@ unsigned int arch_hugetlb_cma_order(void);
 
 #else /* !CONFIG_HUGETLB_PAGE */
 
+static inline void hugetlb_lock_irq(void)
+{
+}
+
+static inline void hugetlb_unlock_irq(void)
+{
+}
+
 static inline void hugetlb_dup_vma_private(struct vm_area_struct *vma)
 {
 }
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 944e6e1d4971..1dd0e7b99bb1 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2725,13 +2725,17 @@ int unpoison_memory(unsigned long pfn)
 
 	ghp = get_hwpoison_page(p, MF_UNPOISON);
 	if (!ghp) {
+		hugetlb_lock_irq();
 		if (folio_test_hugetlb(folio)) {
 			huge = true;
 			count = folio_free_raw_hwp(folio, false);
-			if (count == 0)
+			if (count == 0) {
+				hugetlb_unlock_irq();
 				goto unlock_mutex;
+			}
 		}
 		ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
+		hugetlb_unlock_irq();
 	} else if (ghp < 0) {
 		if (ghp == -EHWPOISON) {
 			ret = put_page_back_buddy(p) ? 0 : -EBUSY;

[PATCH v7 07/13] mm: Remove locking mf_mutex in is_raw_hwpoison_page_in_hugepage()

[Matthew Wilcox (Oracle)]

Sleeping in this kind of predicate is unexpected.  Add a new spinlock
to protect access to the list, and turn it into a normal singly linked
list now that it doesn't need to be a lockless list.

Rename is_raw_hwpoison_page_in_hugepage() to hugetlb_page_hwpoison()
and make it take the folio (since the callers naturally have the folio).
Also remove the handling of non-hugetlb folios and make the arguments
const.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/hugetlbfs/inode.c     |   4 +-
 include/linux/hugetlb.h  |   5 +-
 include/linux/mm_types.h |   4 +-
 mm/memory-failure.c      | 101 ++++++++++++++++++++++-----------------
 4 files changed, 61 insertions(+), 53 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index fbac554886c3..dbca3f713bbf 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -198,7 +198,7 @@ static size_t adjust_range_hwpoison(struct folio *folio, size_t offset,
 	struct page *page = folio_page(folio, offset / PAGE_SIZE);
 	size_t safe_bytes;
 
-	if (is_raw_hwpoison_page_in_hugepage(page))
+	if (hugetlb_page_hwpoison(folio, page))
 		return 0;
 	/* Safe to read the remaining bytes in this page. */
 	safe_bytes = PAGE_SIZE - (offset % PAGE_SIZE);
@@ -206,7 +206,7 @@ static size_t adjust_range_hwpoison(struct folio *folio, size_t offset,
 
 	/* Check each remaining page as long as we are not done yet. */
 	for (; safe_bytes < bytes; safe_bytes += PAGE_SIZE, page++)
-		if (is_raw_hwpoison_page_in_hugepage(page))
+		if (hugetlb_page_hwpoison(folio, page))
 			break;
 
 	return min(safe_bytes, bytes);
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 18661a7cdb37..325f0404a7eb 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1069,10 +1069,7 @@ void hugetlb_register_node(struct node *node);
 void hugetlb_unregister_node(struct node *node);
 #endif
 
-/*
- * Check if a given raw @page in a hugepage is HWPOISON.
- */
-bool is_raw_hwpoison_page_in_hugepage(struct page *page);
+bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page);
 
 static inline unsigned long huge_page_mask_align(struct file *file)
 {
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index b18c2b2e7d2c..86a2d0fee557 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -387,7 +387,7 @@ typedef unsigned short mm_id_t;
  * @_hugetlb_subpool: Do not use directly, use accessor in hugetlb.h.
  * @_hugetlb_cgroup: Do not use directly, use accessor in hugetlb_cgroup.h.
  * @_hugetlb_cgroup_rsvd: Do not use directly, use accessor in hugetlb_cgroup.h.
- * @_hugetlb_hwpoison: Do not use directly, call raw_hwp_list_head().
+ * @hugetlb_hwpoison: List of pages with hwpoison.
  * @_deferred_list: Folios to be split under memory pressure.
  * @_unused_slab_obj_exts: Placeholder to match obj_exts in struct slab.
  *
@@ -499,7 +499,7 @@ struct folio {
 			void *_hugetlb_subpool;
 			void *_hugetlb_cgroup;
 			void *_hugetlb_cgroup_rsvd;
-			void *_hugetlb_hwpoison;
+			struct hwp_page *hugetlb_hwpoison;
 	/* private: the union with struct page is transitional */
 		};
 		struct page __page_3;
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index fda6698e5e0f..30470f8ea590 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1808,63 +1808,60 @@ EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
 
 #ifdef CONFIG_HUGETLB_PAGE
 
+/* Protects all lists of hwp_pages */
+static DEFINE_SPINLOCK(hwp_page_lock);
+
 /*
- * Struct raw_hwp_page represents information about "raw error page",
- * constructing singly linked list from ->_hugetlb_hwpoison field of folio.
+ * hwp_page represents information about "error page",
+ * constructing singly linked list from folio->hugetlb_hwpoison field.
  */
-struct raw_hwp_page {
-	struct llist_node node;
+struct hwp_page {
+	struct hwp_page *next;
 	struct page *page;
 };
 
-static inline struct llist_head *raw_hwp_list_head(struct folio *folio)
-{
-	return (struct llist_head *)&folio->_hugetlb_hwpoison;
-}
-
-bool is_raw_hwpoison_page_in_hugepage(struct page *page)
+/*
+ * Check if a given @page in a hugetlb folio is HWPOISON.
+ */
+bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page)
 {
-	struct llist_head *raw_hwp_head;
-	struct raw_hwp_page *p;
-	struct folio *folio = page_folio(page);
-	bool ret = false;
+	const struct hwp_page *p;
+	unsigned long flags;
 
 	if (!folio_test_has_hwpoisoned(folio))
 		return false;
 
-	if (!folio_test_hugetlb(folio))
-		return PageHWPoison(page);
+	spin_lock_irqsave(&hwp_page_lock, flags);
 
 	/*
-	 * When RawHwpUnreliable is set, kernel lost track of which subpages
-	 * are HWPOISON. So return as if ALL subpages are HWPOISONed.
+	 * When RawHwpUnreliable is set, kernel lost track of which pages
+	 * are HWPOISON. So return as if ALL pages are HWPOISONed.
 	 */
-	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
+	if (folio_test_hugetlb_raw_hwp_unreliable(folio)) {
+		spin_unlock_irqrestore(&hwp_page_lock, flags);
 		return true;
+	}
 
-	mutex_lock(&mf_mutex);
-
-	raw_hwp_head = raw_hwp_list_head(folio);
-	llist_for_each_entry(p, raw_hwp_head->first, node) {
-		if (page == p->page) {
-			ret = true;
+	for (p = folio->hugetlb_hwpoison; p; p = p->next) {
+		if (page == p->page)
 			break;
-		}
 	}
+	spin_unlock_irqrestore(&hwp_page_lock, flags);
 
-	mutex_unlock(&mf_mutex);
-
-	return ret;
+	return p != NULL;
 }
 
 static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
 {
-	struct llist_node *head;
-	struct raw_hwp_page *p, *next;
+	struct hwp_page *p, *next;
 	unsigned long count = 0;
 
-	head = llist_del_all(raw_hwp_list_head(folio));
-	llist_for_each_entry_safe(p, next, head, node) {
+	next = folio->hugetlb_hwpoison;
+	folio->hugetlb_hwpoison = NULL;
+
+	while (next) {
+		p = next;
+		next = p->next;
 		if (move_flag)
 			SetPageHWPoison(p->page);
 		else
@@ -1905,9 +1902,8 @@ static inline int hugetlb_clear_poison(struct folio *folio)
  */
 static int hugetlb_update_hwpoison(struct folio *folio, struct page *page)
 {
-	struct llist_head *head;
-	struct raw_hwp_page *raw_hwp;
-	struct raw_hwp_page *p;
+	struct hwp_page *p;
+	unsigned long flags;
 	int ret = hugetlb_set_poison(folio);
 
 	/*
@@ -1917,16 +1913,23 @@ static int hugetlb_update_hwpoison(struct folio *folio, struct page *page)
 	 */
 	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
 		return MF_HUGETLB_FOLIO_PRE_POISONED;
-	head = raw_hwp_list_head(folio);
-	llist_for_each_entry(p, head->first, node) {
+
+	spin_lock_irqsave(&hwp_page_lock, flags);
+	for (p = folio->hugetlb_hwpoison; p; p = p->next) {
 		if (p->page == page)
-			return MF_HUGETLB_PAGE_PRE_POISONED;
+			break;
 	}
 
-	raw_hwp = kmalloc_obj(struct raw_hwp_page, GFP_ATOMIC);
-	if (raw_hwp) {
-		raw_hwp->page = page;
-		llist_add(&raw_hwp->node, head);
+	if (p) {
+		spin_unlock_irqrestore(&hwp_page_lock, flags);
+		return MF_HUGETLB_PAGE_PRE_POISONED;
+	}
+
+	p = kmalloc_obj(*p, GFP_ATOMIC);
+	if (p) {
+		p->page = page;
+		p->next = folio->hugetlb_hwpoison;
+		folio->hugetlb_hwpoison = p;
 	} else {
 		/*
 		 * Failed to save raw error info.  We no longer trace all
@@ -1935,16 +1938,20 @@ static int hugetlb_update_hwpoison(struct folio *folio, struct page *page)
 		 */
 		folio_set_hugetlb_raw_hwp_unreliable(folio);
 		/*
-		 * Once hugetlb_raw_hwp_unreliable is set, raw_hwp_page is not
+		 * Once hugetlb_raw_hwp_unreliable is set, hwp_page is not
 		 * used any more, so free it.
 		 */
 		__folio_free_raw_hwp(folio, false);
 	}
+	spin_unlock_irqrestore(&hwp_page_lock, flags);
 	return ret;
 }
 
 static unsigned long folio_free_raw_hwp(struct folio *folio, bool move_flag)
 {
+	unsigned long count;
+	unsigned long flags;
+
 	/*
 	 * hugetlb_vmemmap_optimized hugepages can't be freed because struct
 	 * pages for tail pages are required but they don't exist.
@@ -1959,7 +1966,11 @@ static unsigned long folio_free_raw_hwp(struct folio *folio, bool move_flag)
 	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
 		return 0;
 
-	return __folio_free_raw_hwp(folio, move_flag);
+	spin_lock_irqsave(&hwp_page_lock, flags);
+	count = __folio_free_raw_hwp(folio, move_flag);
+	spin_unlock_irqrestore(&hwp_page_lock, flags);
+
+	return count;
 }
 
 void folio_clear_hugetlb_hwpoison(struct folio *folio)
-- 
2.47.3

[PATCH v7 08/13] mm: Check individual hugetlb pages for poison

[Matthew Wilcox (Oracle)]

So far, is_page_hwpoison() has returned true for the entire poisoned
hugetlb folio, but we can usually allow access to the pages which
aren't poisoned.  It's slightly tricky due to not having a reference
to the folio, but the hugetlb lock can save us here.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/page-flags.h |  4 +++-
 mm/memory-failure.c        | 43 +++++++++++++++++++++++++++++++-------
 2 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 4fab3fbfd430..ee026ba9b0b5 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1094,6 +1094,8 @@ static inline bool PageHuge(const struct page *page)
 	return folio_test_hugetlb(page_folio(page));
 }
 
+bool hugetlb_unref_page_hwpoison(const struct page *page);
+
 /*
  * Check if a page is currently marked HWPoisoned.  This check is best
  * effort only and inherently racy: there is no way to synchronize with
@@ -1108,7 +1110,7 @@ static inline bool is_page_hwpoison(const struct page *page)
 		return true;
 	folio = page_folio(page);
 	if (folio_test_huge_poison(folio))
-		return true;
+		return hugetlb_unref_page_hwpoison(page);
 	/* In case we raced with hugetlb transferring flags */
 	return PageHWPoison(page);
 }
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 30470f8ea590..ab2094ed320c 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1820,17 +1820,12 @@ struct hwp_page {
 	struct page *page;
 };
 
-/*
- * Check if a given @page in a hugetlb folio is HWPOISON.
- */
-bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page)
+static bool precise_page_poisoned(const struct folio *folio,
+		const struct page *page)
 {
 	const struct hwp_page *p;
 	unsigned long flags;
 
-	if (!folio_test_has_hwpoisoned(folio))
-		return false;
-
 	spin_lock_irqsave(&hwp_page_lock, flags);
 
 	/*
@@ -1851,6 +1846,40 @@ bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page)
 	return p != NULL;
 }
 
+/*
+ * Check if a given @page in a hugetlb folio is HWPOISON.
+ */
+bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page)
+{
+	if (!folio_test_has_hwpoisoned(folio))
+		return false;
+
+	return precise_page_poisoned(folio, page);
+}
+
+/*
+ * We have no reference on the folio containing this page.
+ * The hugetlb_lock keeps hugetlb folios from being freed.
+ */
+bool hugetlb_unref_page_hwpoison(const struct page *page)
+{
+	const struct folio *folio;
+	unsigned long flags;
+	bool ret;
+
+	spin_lock_irqsave(&hugetlb_lock, flags);
+	folio = page_folio(page);
+	if (!folio_test_huge_poison(folio)) {
+		ret = PageHWPoison(page);
+		goto unlock;
+	}
+
+	ret = precise_page_poisoned(folio, page);
+unlock:
+	spin_unlock_irqrestore(&hugetlb_lock, flags);
+	return ret;
+}
+
 static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
 {
 	struct hwp_page *p, *next;
-- 
2.47.3

[PATCH v7 09/13] filemap: Add hwpoison handling to filemap_read()

[Matthew Wilcox (Oracle)]

From: Jane Chu <jane.chu@oracle.com>

Add hwpoison handling to filemap_read() such that .read_iter() could
make best effort copying data out of clean pages without risking
MCE in case page cache contains HWpoison.

Signed-off-by: Jane Chu <jane.chu@oracle.com>
Co-developed-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Matthew Wilcox <willy@infradead.org>
---
 include/linux/hugetlb.h    |  2 --
 include/linux/page-flags.h | 11 +++++++++++
 mm/filemap.c               | 33 +++++++++++++++++++++++++++++++--
 3 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 325f0404a7eb..1878642e75ec 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1069,8 +1069,6 @@ void hugetlb_register_node(struct node *node);
 void hugetlb_unregister_node(struct node *node);
 #endif
 
-bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page);
-
 static inline unsigned long huge_page_mask_align(struct file *file)
 {
 	return PAGE_MASK & ~huge_page_mask(hstate_file(file));
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index ee026ba9b0b5..07cc7854b2de 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1094,6 +1094,7 @@ static inline bool PageHuge(const struct page *page)
 	return folio_test_hugetlb(page_folio(page));
 }
 
+bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page);
 bool hugetlb_unref_page_hwpoison(const struct page *page);
 
 /*
@@ -1115,6 +1116,16 @@ static inline bool is_page_hwpoison(const struct page *page)
 	return PageHWPoison(page);
 }
 
+static inline bool is_ref_page_hwpoison(const struct folio *folio,
+		const struct page *page)
+{
+	if (PageHWPoison(page))
+		return true;
+	if (folio_test_hugetlb(folio))
+		return hugetlb_page_hwpoison(folio, page);
+	return false;
+}
+
 static inline bool folio_has_hwpoisoned_page(const struct folio *folio)
 {
 	return PageHWPoison(&folio->page) ||
diff --git a/mm/filemap.c b/mm/filemap.c
index 58eb9d240643..26a5f18121f9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2483,6 +2483,8 @@ static void filemap_get_read_batch(struct address_space *mapping,
 
 		if (!folio_batch_add(fbatch, folio))
 			break;
+		if (folio_has_hwpoisoned_page(folio))
+			break;
 		if (!folio_test_uptodate(folio))
 			break;
 		if (folio_test_readahead(folio))
@@ -2749,6 +2751,29 @@ static inline bool pos_same_folio(loff_t pos1, loff_t pos2, struct folio *folio)
 	return (pos1 >> shift == pos2 >> shift);
 }
 
+static size_t adjust_range_hwpoison(const struct folio *folio, size_t offset,
+		size_t bytes)
+{
+	const struct page *page = folio_page(folio, offset / PAGE_SIZE);
+	size_t safe_bytes;
+
+	if (!folio_has_hwpoisoned_page(folio))
+		return bytes;
+	if (is_ref_page_hwpoison(folio, page))
+		return 0;
+
+	/* Safe to read the remaining bytes in this page. */
+	safe_bytes = PAGE_SIZE - (offset % PAGE_SIZE);
+	page++;
+
+	/* Check each remaining page as long as we are not done yet. */
+	for (; safe_bytes < bytes; safe_bytes += PAGE_SIZE, page++)
+		if (is_ref_page_hwpoison(folio, page))
+			break;
+
+	return min(safe_bytes, bytes);
+}
+
 static void filemap_end_dropbehind_read(struct folio *folio)
 {
 	if (!folio_test_dropbehind(folio))
@@ -2862,14 +2887,18 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
 			if (writably_mapped)
 				flush_dcache_folio(folio);
 
-			copied = copy_folio_to_iter(folio, offset, bytes, iter);
+			copied = adjust_range_hwpoison(folio, offset, bytes);
+			if (copied < bytes)
+				error = -EIO;
+			copied = copy_folio_to_iter(folio, offset, copied, iter);
 
 			already_read += copied;
 			iocb->ki_pos += copied;
 			last_pos = iocb->ki_pos;
 
 			if (copied < bytes) {
-				error = -EFAULT;
+				if (!error)
+					error = -EFAULT;
 				break;
 			}
 		}
-- 
2.47.3

[PATCH v7 10/13] filemap: Remove checks in mapping_set_folio_order_range()

[Matthew Wilcox (Oracle)]

These checks make it impossible to use mapping_set_folio_order_range()
in hugetlb.  They add very little value and can simply be removed.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/pagemap.h | 34 ++++++++++++++--------------------
 1 file changed, 14 insertions(+), 20 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2c3718d592d6..968b791cfd14 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -373,7 +373,7 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
  * assumptions about maximum order if THP are disabled, but 8 seems like
  * a good order (that's 1MB if you're using 4kB pages)
  */
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#ifdef CONFIG_LARGE_FOLIO
 #define PREFERRED_MAX_PAGECACHE_ORDER	HPAGE_PMD_ORDER
 #else
 #define PREFERRED_MAX_PAGECACHE_ORDER	8
@@ -394,7 +394,7 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
  */
 static inline size_t mapping_max_folio_size_supported(void)
 {
-	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+	if (IS_ENABLED(CONFIG_LARGE_FOLIO))
 		return 1U << (PAGE_SHIFT + MAX_PAGECACHE_ORDER);
 	return PAGE_SIZE;
 }
@@ -405,29 +405,23 @@ static inline size_t mapping_max_folio_size_supported(void)
  * @min: Minimum folio order (between 0-MAX_PAGECACHE_ORDER inclusive).
  * @max: Maximum folio order (between @min-MAX_PAGECACHE_ORDER inclusive).
  *
- * The filesystem should call this function in its inode constructor to
- * indicate which base size (min) and maximum size (max) of folio the VFS
- * can use to cache the contents of the file.  This should only be used
- * if the filesystem needs special handling of folio sizes (ie there is
- * something the core cannot know).
+ * The filesystem should call this function in its inode constructor
+ * to indicate which size folios can be used to cache the contents of
+ * the inode.  This should only be used if the filesystem needs special
+ * handling of folio sizes (ie there is something the core cannot know).
  * Do not tune it based on, eg, i_size.
  *
+ * hugetlb calls this with orders larger than MAX_PAGECACHE_ORDER.
+ * Normal filesystems should not do this.
+ *
  * Context: This should not be called while the inode is active as it
  * is non-atomic.
  */
 static inline void mapping_set_folio_order_range(struct address_space *mapping,
-						 unsigned int min,
-						 unsigned int max)
+		unsigned int min, unsigned int max)
 {
-	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+	if (!IS_ENABLED(CONFIG_LARGE_FOLIO))
 		return;
-
-	if (min > MAX_PAGECACHE_ORDER)
-		min = MAX_PAGECACHE_ORDER;
-
-	if (max > MAX_PAGECACHE_ORDER)
-		max = MAX_PAGECACHE_ORDER;
-
 	if (max < min)
 		max = min;
 
@@ -460,7 +454,7 @@ static inline void mapping_set_large_folios(struct address_space *mapping)
 static inline unsigned int
 mapping_max_folio_order(const struct address_space *mapping)
 {
-	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+	if (!IS_ENABLED(CONFIG_LARGE_FOLIO))
 		return 0;
 	return (mapping->flags & AS_FOLIO_ORDER_MAX_MASK) >> AS_FOLIO_ORDER_MAX;
 }
@@ -468,7 +462,7 @@ mapping_max_folio_order(const struct address_space *mapping)
 static inline unsigned int
 mapping_min_folio_order(const struct address_space *mapping)
 {
-	if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
+	if (!IS_ENABLED(CONFIG_LARGE_FOLIO))
 		return 0;
 	return (mapping->flags & AS_FOLIO_ORDER_MIN_MASK) >> AS_FOLIO_ORDER_MIN;
 }
@@ -524,7 +518,7 @@ static inline bool mapping_large_folio_support(const struct address_space *mappi
  *
  * Return: True if PMD-sized folios are supported, otherwise false.
  */
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#ifdef CONFIG_LARGE_FOLIO
 static inline bool mapping_pmd_folio_support(const struct address_space *mapping)
 {
 	/* AS_FOLIO_ORDER is only reasonable for pagecache folios */
-- 
2.47.3

[PATCH v7 11/13] hugetlb: Set mapping folio order

[Matthew Wilcox (Oracle)]

hugetlbfs currently uses an fs-specific way to determine the size of
the folios in its page cache.  Thanks to the support of block sizes
larger than page sizes, we now support this as part of the page cache.
It's somewhat more efficient as we have this information directly in the
mapping rather than going from inode->i_sb->s_fs_info.  We can convert
the rest of the hugetlb code to use this at our leisure; this is needed
now so that we can use filemap_get_pages() unmodified.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Gregory Price <gourry@gourry.net>
---
 fs/hugetlbfs/inode.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index dbca3f713bbf..8d15413a67ee 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -883,6 +883,16 @@ static struct inode *hugetlbfs_get_root(struct super_block *sb,
 	return inode;
 }
 
+static void hugetlbfs_init_regular_inode(struct inode *inode)
+{
+	struct hstate *hstate = hstate_inode(inode);
+	unsigned int order = huge_page_order(hstate);
+
+	inode->i_op = &hugetlbfs_inode_operations;
+	inode->i_fop = &hugetlbfs_file_operations;
+	mapping_set_folio_order_range(inode->i_mapping, order, order);
+}
+
 /*
  * Hugetlbfs is not reclaimable; therefore its i_mmap_rwsem will never
  * be taken from reclaim -- unlike regular filesystems. This needs an
@@ -926,8 +936,7 @@ static struct inode *hugetlbfs_get_inode(struct super_block *sb,
 			init_special_inode(inode, mode, dev);
 			break;
 		case S_IFREG:
-			inode->i_op = &hugetlbfs_inode_operations;
-			inode->i_fop = &hugetlbfs_file_operations;
+			hugetlbfs_init_regular_inode(inode);
 			break;
 		case S_IFDIR:
 			inode->i_op = &hugetlbfs_dir_inode_operations;
-- 
2.47.3

[PATCH v7 12/13] filemap: Add support for authoritative mappings

[Matthew Wilcox (Oracle)]

An authoritative mapping knows about all the folios in the mapping.
If read() finds a missing folio, there's no reason to allocate one and
try to read it because we know it's a zero region of the file.  We can
just call iov_iter_zero() instead.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/pagemap.h | 11 +++++++++++
 mm/filemap.c            | 18 ++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 968b791cfd14..22d48935ffda 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -210,6 +210,7 @@ enum mapping_flags {
 	AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM = 9,
 	AS_KERNEL_FILE = 10,	/* mapping for a fake kernel file that shouldn't
 				   account usage to user cgroups */
+	AS_AUTHORITATIVE = 11,	/* If we miss in the page cache, it's a hole */
 	/* Bits 16-25 are used for FOLIO_ORDER */
 	AS_FOLIO_ORDER_BITS = 5,
 	AS_FOLIO_ORDER_MIN = 16,
@@ -345,6 +346,16 @@ static inline bool mapping_writeback_may_deadlock_on_reclaim(const struct addres
 	return test_bit(AS_WRITEBACK_MAY_DEADLOCK_ON_RECLAIM, &mapping->flags);
 }
 
+static inline void mapping_set_authoritative(struct address_space *mapping)
+{
+	set_bit(AS_AUTHORITATIVE, &mapping->flags);
+}
+
+static inline bool mapping_is_authoritative(const struct address_space *mapping)
+{
+	return test_bit(AS_AUTHORITATIVE, &mapping->flags);
+}
+
 static inline gfp_t mapping_gfp_mask(const struct address_space *mapping)
 {
 	return mapping->gfp_mask;
diff --git a/mm/filemap.c b/mm/filemap.c
index 26a5f18121f9..5a8cc20e624e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2697,6 +2697,8 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count,
 	if (!folio_batch_count(fbatch)) {
 		DEFINE_READAHEAD(ractl, filp, &filp->f_ra, mapping, index);
 
+		if (mapping_is_authoritative(mapping))
+			return 0;
 		if (iocb->ki_flags & IOCB_NOIO)
 			return -EAGAIN;
 		if (iocb->ki_flags & IOCB_NOWAIT)
@@ -2853,6 +2855,22 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
 			goto put_folios;
 		end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count);
 
+		if (!folio_batch_count(&fbatch)) {
+			size_t fsize = mapping_min_folio_nrbytes(mapping);
+			size_t offset = iocb->ki_pos & (fsize - 1);
+			size_t bytes = min_t(loff_t, end_offset - iocb->ki_pos,
+					     fsize - offset);
+			size_t copied = iov_iter_zero(bytes, iter);
+
+			already_read += copied;
+			iocb->ki_pos += copied;
+			last_pos = iocb->ki_pos;
+
+			if (copied < bytes)
+				error = -EFAULT;
+			continue;
+		}
+
 		/*
 		 * Once we start copying data, we don't want to be touching any
 		 * cachelines that might be contended:
-- 
2.47.3

[PATCH v7 13/13] hugetlb: replace hugetlbfs_read_iter() with generic_file_read_iter()

[Matthew Wilcox (Oracle)]

From: Jane Chu <jane.chu@oracle.com>

generic_file_read_iter() now handles hugetlb poison, hugetlb page
size and missing folios correctly, so we no longer need a separate
hugetlbfs_read_iter().

Signed-off-by: Jane Chu <jane.chu@oracle.com>
Co-developed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/hugetlbfs/inode.c | 110 +------------------------------------------
 1 file changed, 2 insertions(+), 108 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 8d15413a67ee..cef7e61b827d 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -187,113 +187,6 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 	return mm_get_unmapped_area_vmflags(file, addr0, len, pgoff, flags, 0);
 }
 
-/*
- * Someone wants to read @bytes from a HWPOISON hugetlb @folio from @offset.
- * Returns the maximum number of bytes one can read without touching the 1st raw
- * HWPOISON page.
- */
-static size_t adjust_range_hwpoison(struct folio *folio, size_t offset,
-		size_t bytes)
-{
-	struct page *page = folio_page(folio, offset / PAGE_SIZE);
-	size_t safe_bytes;
-
-	if (hugetlb_page_hwpoison(folio, page))
-		return 0;
-	/* Safe to read the remaining bytes in this page. */
-	safe_bytes = PAGE_SIZE - (offset % PAGE_SIZE);
-	page++;
-
-	/* Check each remaining page as long as we are not done yet. */
-	for (; safe_bytes < bytes; safe_bytes += PAGE_SIZE, page++)
-		if (hugetlb_page_hwpoison(folio, page))
-			break;
-
-	return min(safe_bytes, bytes);
-}
-
-/*
- * Support for read() - Find the page attached to f_mapping and copy out the
- * data. This provides functionality similar to filemap_read().
- */
-static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
-{
-	struct file *file = iocb->ki_filp;
-	struct hstate *h = hstate_file(file);
-	struct address_space *mapping = file->f_mapping;
-	struct inode *inode = mapping->host;
-	unsigned long index = iocb->ki_pos >> huge_page_shift(h);
-	unsigned long offset = iocb->ki_pos & ~huge_page_mask(h);
-	unsigned long end_index;
-	loff_t isize;
-	ssize_t retval = 0;
-
-	while (iov_iter_count(to)) {
-		struct folio *folio;
-		size_t nr, copied, want;
-
-		/* nr is the maximum number of bytes to copy from this page */
-		nr = huge_page_size(h);
-		isize = i_size_read(inode);
-		if (!isize)
-			break;
-		end_index = (isize - 1) >> huge_page_shift(h);
-		if (index > end_index)
-			break;
-		if (index == end_index) {
-			nr = ((isize - 1) & ~huge_page_mask(h)) + 1;
-			if (nr <= offset)
-				break;
-		}
-		nr = nr - offset;
-
-		/* Find the folio */
-		folio = filemap_lock_hugetlb_folio(h, mapping, index);
-		if (IS_ERR(folio)) {
-			/*
-			 * We have a HOLE, zero out the user-buffer for the
-			 * length of the hole or request.
-			 */
-			copied = iov_iter_zero(nr, to);
-		} else {
-			folio_unlock(folio);
-
-			if (!folio_test_has_hwpoisoned(folio))
-				want = nr;
-			else {
-				/*
-				 * Adjust how many bytes safe to read without
-				 * touching the 1st raw HWPOISON page after
-				 * offset.
-				 */
-				want = adjust_range_hwpoison(folio, offset, nr);
-				if (want == 0) {
-					folio_put(folio);
-					retval = -EIO;
-					break;
-				}
-			}
-
-			/*
-			 * We have the folio, copy it to user space buffer.
-			 */
-			copied = copy_folio_to_iter(folio, offset, want, to);
-			folio_put(folio);
-		}
-		offset += copied;
-		retval += copied;
-		if (copied != nr && iov_iter_count(to)) {
-			if (!retval)
-				retval = -EFAULT;
-			break;
-		}
-		index += offset >> huge_page_shift(h);
-		offset &= ~huge_page_mask(h);
-	}
-	iocb->ki_pos = ((loff_t)index << huge_page_shift(h)) + offset;
-	return retval;
-}
-
 static int hugetlbfs_write_begin(const struct kiocb *iocb,
 			struct address_space *mapping,
 			loff_t pos, unsigned len,
@@ -891,6 +784,7 @@ static void hugetlbfs_init_regular_inode(struct inode *inode)
 	inode->i_op = &hugetlbfs_inode_operations;
 	inode->i_fop = &hugetlbfs_file_operations;
 	mapping_set_folio_order_range(inode->i_mapping, order, order);
+	mapping_set_authoritative(inode->i_mapping);
 }
 
 /*
@@ -1215,7 +1109,7 @@ static void init_once(void *foo)
 }
 
 static const struct file_operations hugetlbfs_file_operations = {
-	.read_iter		= hugetlbfs_read_iter,
+	.read_iter		= generic_file_read_iter,
 	.mmap			= hugetlbfs_file_mmap,
 	.fsync			= noop_fsync,
 	.get_unmapped_area	= hugetlb_get_unmapped_area,
-- 
2.47.3

Re: [PATCH v7 00/13] Use generic_file_read_iter() in hugetlbfs

[Matthew Wilcox]

On Tue, Jul 28, 2026 at 09:43:52PM +0100, Matthew Wilcox (Oracle) wrote:
> This set of patches are separated out from Jane's earlier series.
> https://lore.kernel.org/linux-mm/20260617172534.1740152-1-jane.chu@oracle.com/

Sashiko pointed out that I hadn't touched kpageflags, and it's right.
I'll add this standalone patch for v8:

commit c392dd16cf5f
Author: Matthew Wilcox (Oracle) <willy@infradead.org>
Date:   Wed Jul 29 11:12:01 2026 -0400

    kpageflags: Use is_page_hwpoison() to set KPF_HWPOISON
    
    Instead of knowing how hugetlb handles hwpoison, just ask
    is_page_hwpoison().  This gives us the flexibility to change how hwpoison
    is handled without updating this function in the future.
    
    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

diff --git a/fs/proc/page.c b/fs/proc/page.c
index 7d9387143435..28c9a7b724f3 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -233,12 +233,8 @@ u64 stable_page_flags(const struct page *page)
 	u |= kpf_copy_bit(k, KPF_UNEVICTABLE,	PG_unevictable);
 	u |= kpf_copy_bit(k, KPF_MLOCKED,	PG_mlocked);
 
-#ifdef CONFIG_MEMORY_FAILURE
-	if (u & (1 << KPF_HUGE))
-		u |= kpf_copy_bit(k, KPF_HWPOISON,	PG_hwpoison);
-	else
-		u |= kpf_copy_bit(ps.page_snapshot.flags.f, KPF_HWPOISON, PG_hwpoison);
-#endif
+	if (is_page_hwpoison(page))
+		u |= KPF_HWPOISON;
 
 	u |= kpf_copy_bit(k, KPF_RESERVED,	PG_reserved);
 	u |= kpf_copy_bit(k, KPF_OWNER_2,	PG_owner_2);