[PATCH v3 0/9] Use generic_file_read_iter() in hugetlbfs

[PATCH v3 0/9] 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/

There's enough potentially controversial things in here that I think
it's worth considering them by themselves.  First, handling hwpoison
in filemap_read().  I want this for shmem as well as for hugetlbfs (a
later patchset, maybe).  Second, handling misses in the pagecache as
holes rather than opportunities to populate the pagecache.

Sashiko review of v2 here: 
https://sashiko.dev/#/patchset/20260709184740.1286561-1-willy%40infradead.org

Changes:
 - Introduce CONFIG_FILEMAP_LARGE_FOLIO
 - Reordered the patches to do all the hwpoison handling first
 - Picked up Usama's Acked-by on a couple of patches
 - Rewrote handling of hugetlb hwpoison completely
 - Return -EIO instead of -EFAULT when a read touches a hwpoison page
 - Add a call to mapping_set_authoritative() in hugetlbfs

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

Matthew Wilcox (Oracle) (7):
  mm: Rename folio_contain_hwpoison_page() to folio_has_hwpoison_page()
  hugetlb: Mark some function arguments as const
  memory-failure: Track hugetlb poison in a hash table
  mm: Handle hugetlb correctly in is_page_hwpoison()
  filemap: Remove checks in mapping_set_folio_order_range()
  hugetlb: Set mapping folio order
  filemap: Add support for authoritative mappings

 fs/Kconfig                 |   1 +
 fs/hugetlbfs/inode.c       | 122 ++++---------------------------------
 include/linux/hugetlb.h    |  24 +++-----
 include/linux/mm_types.h   |   2 -
 include/linux/page-flags.h |  28 ++++++---
 include/linux/pagemap.h    |  45 ++++++++------
 mm/Kconfig                 |   4 ++
 mm/filemap.c               |  51 +++++++++++++++-
 mm/huge_memory.c           |   2 +-
 mm/hugetlb.c               |   2 +-
 mm/memory-failure.c        |  80 ++++++++++++------------
 mm/memory_hotplug.c        |   2 +-
 mm/shmem.c                 |   2 +-
 mm/vmscan.c                |   2 +-
 14 files changed, 167 insertions(+), 200 deletions(-)

-- 
2.47.3

[PATCH v3 1/9] 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>
---
 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 v3 2/9] 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>
---
 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 v3 3/9] memory-failure: Track hugetlb poison in a hash table

[Matthew Wilcox (Oracle)]

With HVO, we cannot track per-page hwpoison as the struct pages are no
longer there.  Instead, they were being tracked in a linked list
anchored in the folio.  Unfortunately, we need to be able to determine
whether pages are hwpoison without holding a reference to the folio and
there's no way to atomically check whether a folio is hugetlb and get
the list of hwpoison pages.

Switch to a global hashtable of hwpoison pages which is only queried
when the folio indicates that it has pages in that hashtable.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/mm_types.h |  2 --
 mm/memory-failure.c      | 71 +++++++++++++++++++++-------------------
 2 files changed, 37 insertions(+), 36 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index b18c2b2e7d2c..ed5c0829ff56 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -387,7 +387,6 @@ 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().
  * @_deferred_list: Folios to be split under memory pressure.
  * @_unused_slab_obj_exts: Placeholder to match obj_exts in struct slab.
  *
@@ -499,7 +498,6 @@ struct folio {
 			void *_hugetlb_subpool;
 			void *_hugetlb_cgroup;
 			void *_hugetlb_cgroup_rsvd;
-			void *_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 51508a55c405..490aed0b25b4 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -43,6 +43,7 @@
 #include <linux/sched/signal.h>
 #include <linux/sched/task.h>
 #include <linux/dax.h>
+#include <linux/hashtable.h>
 #include <linux/ksm.h>
 #include <linux/rmap.h>
 #include <linux/export.h>
@@ -1808,24 +1809,18 @@ EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
 
 #ifdef CONFIG_HUGETLB_PAGE
 
-/*
- * Struct raw_hwp_page represents information about "raw error page",
- * constructing singly linked list from ->_hugetlb_hwpoison field of folio.
- */
-struct raw_hwp_page {
-	struct llist_node node;
+/* Protects hugetlb_hwpoison list */
+static DEFINE_SPINLOCK(htlb_hwpoison_lock);
+static DEFINE_HASHTABLE(htlb_hwpoison, 5);
+
+struct hwp_page {
+	struct hlist_node node;
 	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)
 {
-	struct llist_head *raw_hwp_head;
-	struct raw_hwp_page *p;
+	struct hwp_page *p;
 	struct folio *folio = page_folio(page);
 	bool ret = false;
 
@@ -1842,36 +1837,39 @@ bool is_raw_hwpoison_page_in_hugepage(struct page *page)
 	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
 		return true;
 
-	mutex_lock(&mf_mutex);
+	spin_lock(&htlb_hwpoison_lock);
 
-	raw_hwp_head = raw_hwp_list_head(folio);
-	llist_for_each_entry(p, raw_hwp_head->first, node) {
+	hash_for_each_possible(htlb_hwpoison, p, node, (unsigned long)page) {
 		if (page == p->page) {
 			ret = true;
 			break;
 		}
 	}
 
-	mutex_unlock(&mf_mutex);
+	spin_unlock(&htlb_hwpoison_lock);
 
 	return ret;
 }
 
-static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
+static unsigned long __folio_free_hwp(struct folio *folio, bool move_flag)
 {
-	struct llist_node *head;
-	struct raw_hwp_page *p, *next;
+	int b;
+	struct hwp_page *p;
+	struct hlist_node *tmp;
 	unsigned long count = 0;
 
-	head = llist_del_all(raw_hwp_list_head(folio));
-	llist_for_each_entry_safe(p, next, head, node) {
+	hash_for_each_safe(htlb_hwpoison, b, tmp, p, node) {
+		if (page_folio(p->page) != folio)
+			continue;
 		if (move_flag)
 			SetPageHWPoison(p->page);
 		else
 			num_poisoned_pages_sub(page_to_pfn(p->page), 1);
+		hash_del(&p->node);
 		kfree(p);
 		count++;
 	}
+
 	return count;
 }
 
@@ -1887,9 +1885,7 @@ static unsigned long __folio_free_raw_hwp(struct folio *folio, bool move_flag)
  */
 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;
 	int ret = folio_test_set_hwpoison(folio) ? MF_HUGETLB_FOLIO_PRE_POISONED : 0;
 
 	/*
@@ -1899,16 +1895,18 @@ 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) {
-		if (p->page == page)
+	spin_lock(&htlb_hwpoison_lock);
+	hash_for_each_possible(htlb_hwpoison, p, node, (unsigned long)page) {
+		if (p->page == page) {
+			spin_unlock(&htlb_hwpoison_lock);
 			return MF_HUGETLB_PAGE_PRE_POISONED;
+		}
 	}
 
-	raw_hwp = kmalloc_obj(struct raw_hwp_page, GFP_ATOMIC);
-	if (raw_hwp) {
-		raw_hwp->page = page;
-		llist_add(&raw_hwp->node, head);
+	p = kmalloc_obj(struct hwp_page, GFP_ATOMIC);
+	if (p) {
+		p->page = page;
+		hash_add(htlb_hwpoison, &p->node, (unsigned long)page);
 	} else {
 		/*
 		 * Failed to save raw error info.  We no longer trace all
@@ -1920,13 +1918,15 @@ static int hugetlb_update_hwpoison(struct folio *folio, struct page *page)
 		 * Once hugetlb_raw_hwp_unreliable is set, raw_hwp_page is not
 		 * used any more, so free it.
 		 */
-		__folio_free_raw_hwp(folio, false);
+		__folio_free_hwp(folio, false);
 	}
+	spin_unlock(&htlb_hwpoison_lock);
 	return ret;
 }
 
 static unsigned long folio_free_raw_hwp(struct folio *folio, bool move_flag)
 {
+	unsigned long count;
 	/*
 	 * hugetlb_vmemmap_optimized hugepages can't be freed because struct
 	 * pages for tail pages are required but they don't exist.
@@ -1941,7 +1941,10 @@ 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(&htlb_hwpoison_lock);
+	count = __folio_free_hwp(folio, move_flag);
+	spin_unlock(&htlb_hwpoison_lock);
+	return count;
 }
 
 void folio_clear_hugetlb_hwpoison(struct folio *folio)
-- 
2.47.3

[PATCH v3 4/9] mm: Handle hugetlb correctly in is_page_hwpoison()

[Matthew Wilcox (Oracle)]

Checking to see whether a page inside a hugetlb folio is hardware
poisoned is more complicated than I realised.  The correct logic was
in is_raw_hwpoison_page_in_hugepage().  Make is_page_hwpoison() the
official entry point for "is this page hwpoison", no matter what kind
of folio it belongs to.  Rename is_raw_hwpoison_page_in_hugepage() to
hugetlb_page_hwpoison(), and remove the attempt to handle non-hugetlb
folios from it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/hugetlbfs/inode.c       |  4 ++--
 include/linux/hugetlb.h    |  5 -----
 include/linux/page-flags.h | 24 +++++++++++++++++++-----
 mm/memory-failure.c        | 11 +++++------
 4 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 216e1a0dd0b2..f1d4e511d9b1 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..1878642e75ec 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1069,11 +1069,6 @@ 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);
-
 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 4185a03a45cf..8e57c12a7301 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1068,6 +1068,9 @@ static inline bool PageHuge(const struct page *page)
 	return folio_test_hugetlb(page_folio(page));
 }
 
+#ifdef CONFIG_MEMORY_FAILURE
+bool hugetlb_page_hwpoison(const struct folio *folio, 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
@@ -1075,13 +1078,24 @@ static inline bool PageHuge(const struct page *page)
  */
 static inline bool is_page_hwpoison(const struct page *page)
 {
-	const struct folio *folio;
+	const struct folio *folio = page_folio(page);
+
+	if (folio_test_hugetlb(folio))
+		return hugetlb_page_hwpoison(folio, page);
+	return PageHWPoison(page);
+}
+#else
+static inline bool hugetlb_page_hwpoison(const struct folio *folio,
+		const struct page *page)
+{
+	return false;
+}
 
-	if (PageHWPoison(page))
-		return true;
-	folio = page_folio(page);
-	return folio_test_hugetlb(folio) && PageHWPoison(&folio->page);
+static inline bool is_page_hwpoison(const struct page *page)
+{
+	return false;
 }
+#endif
 
 static inline bool folio_has_hwpoisoned_page(const struct folio *folio)
 {
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 490aed0b25b4..9e4ee5d93905 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1818,18 +1818,17 @@ struct hwp_page {
 	struct page *page;
 };
 
-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 hwp_page *p;
-	struct folio *folio = page_folio(page);
+	const struct hwp_page *p;
 	bool ret = false;
 
 	if (!folio_test_hwpoison(folio))
 		return false;
 
-	if (!folio_test_hugetlb(folio))
-		return PageHWPoison(page);
-
 	/*
 	 * When RawHwpUnreliable is set, kernel lost track of which subpages
 	 * are HWPOISON. So return as if ALL subpages are HWPOISONed.
-- 
2.47.3

[PATCH v3 5/9] 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>
---
 mm/filemap.c | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 58eb9d240643..0f3ada4d8cff 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_page_hwpoison(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_page_hwpoison(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 v3 6/9] 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.
Use CONFIG_FILEMAP_LARGE_FOLIO to mean "do we support HUGETLB or THP".

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/Kconfig              |  1 +
 include/linux/pagemap.h | 34 ++++++++++++++--------------------
 mm/Kconfig              |  4 ++++
 3 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/fs/Kconfig b/fs/Kconfig
index cf6ae64776e6..4922adf5bc85 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -272,6 +272,7 @@ endif # HUGETLBFS
 
 config HUGETLB_PAGE
 	def_bool HUGETLBFS
+	select FILEMAP_LARGE_FOLIO
 	select XARRAY_MULTI
 
 config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 2c3718d592d6..346b77fa95ef 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_FILEMAP_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_FILEMAP_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_FILEMAP_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_FILEMAP_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_FILEMAP_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_FILEMAP_LARGE_FOLIO
 static inline bool mapping_pmd_folio_support(const struct address_space *mapping)
 {
 	/* AS_FOLIO_ORDER is only reasonable for pagecache folios */
diff --git a/mm/Kconfig b/mm/Kconfig
index 9e0ca4824905..992e7ae0b2bf 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -843,11 +843,15 @@ config PERSISTENT_HUGE_ZERO_FOLIO
 config MM_ID
 	def_bool n
 
+config FILEMAP_LARGE_FOLIO
+	def_bool n
+
 menuconfig TRANSPARENT_HUGEPAGE
 	bool "Transparent Hugepage Support"
 	depends on HAVE_ARCH_TRANSPARENT_HUGEPAGE && !PREEMPT_RT
 	select COMPACTION
 	select XARRAY_MULTI
+	select FILEMAP_LARGE_FOLIO
 	select MM_ID
 	help
 	  Transparent Hugepages allows the kernel to use huge pages and
-- 
2.47.3

[PATCH v3 7/9] 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>
---
 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 f1d4e511d9b1..725bb945a440 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 v3 8/9] 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 346b77fa95ef..bd6a6275a4e9 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 0f3ada4d8cff..f662cda81dc7 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 v3 9/9] 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 | 109 +------------------------------------------
 1 file changed, 1 insertion(+), 108 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 725bb945a440..a6f0459d79de 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_hwpoison(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,
@@ -1215,7 +1108,7 @@ 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 v3 6/9] filemap: Remove checks in mapping_set_folio_order_range()

[Matthew Wilcox]

On Tue, Jul 14, 2026 at 07:08:36PM +0100, Matthew Wilcox (Oracle) wrote:
>  static inline size_t mapping_max_folio_size_supported(void)
>  {
> -	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE))
> +	if (IS_ENABLED(CONFIG_FILEMAP_LARGE_FOLIO))

oops.  This test suite I'm using clearly isn't much good.

Re: [PATCH v3 9/9] hugetlb: replace hugetlbfs_read_iter() with generic_file_read_iter()

[Matthew Wilcox]

On Tue, Jul 14, 2026 at 07:08:39PM +0100, Matthew Wilcox (Oracle) wrote:
> 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 | 109 +------------------------------------------
>  1 file changed, 1 insertion(+), 108 deletions(-)

What I was _testing_ had this hunk in that I neglected to commit to git
before running format-patch:

@@ -784,6 +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);
 }

 /*