[PATCH v5 00/12] Use generic_file_read_iter() in hugetlbfs

[PATCH v5 00/12] 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/

v4 here:
https://lore.kernel.org/all/20260723143034.175661-1-willy@infradead.org/

Changes from v4:
 - Drop patch "Test the page is hwpoison before taking the mutex".
   It's not necessary for this series, and Sashiko points out a bad
   possibility.
 - Fix try_to_unmap() checking of HWPoison for hugetlb folios
 - Protect the folio->hugetlb_hwpoison list with its own spinlock
 - Fold the "Remove raw_hwp_list_head" patch into the "Remove locking
   mf_mutex in is_raw_hwpoison_page_in_hugepage" patch
 - Make folio_test_huge_poison() always false if CONFIG_MEMORY_FAILURE not set
 - Fix CONFIG_FILEMAP_LARGE_FOLIO -> CONFIG_LARGE_FOLIO conversion
 - Fix hugetlb_clear_poison() to clear has_hwpoisoned last
 - Add tags from Ackerley & Sean for guest_memfd patch

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

Matthew Wilcox (Oracle) (10):
  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: 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               |  16 ++--
 mm/memory-failure.c        | 186 ++++++++++++++++++++++++-------------
 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, 321 insertions(+), 252 deletions(-)

-- 
2.47.3

[PATCH v5 01/12] 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: Naoya Horiguchi <naoya.horiguchi@nec.com>
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 v5 01/12] memory-failure: Fix hardware poison check in unpoison_memory() again

[Matthew Wilcox]

Sashiko:
> --- Patch [1]: [PATCH v5 01/12] memory-failure: Fix hardware poison check in unpoison_memory() again ---
> commit 4beed8e27f2afa68261389ac2133cfe324d37d0e
> Author: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> memory-failure: Fix hardware poison check in unpoison_memory() again
> 
> This commit modifies unpoison_memory() to use is_page_hwpoison() to better
> support hugetlb folios and ensures the HWPoison flag is cleared on the correct
> head page.
> 
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index 51508a55c4055..944e6e1d49719 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",
> 
> Can this speculative evaluation of is_page_hwpoison() trigger a panic?
> 
> Since this is evaluated without a reference on the page, the underlying
> page could be concurrently freed and reallocated as a tail page.
> Looking at is_page_hwpoison() in include/linux/page-flags.h, it calls
> folio_test_hugetlb(folio), which uses const_folio_flags(). That function

No it doesn't.  folio_test_hugetlb() is one of th FOLIO_TYPE_OPS which is
defined as return data_race(folio->page.page_type >> 24) == PGTY_##lname;
and no asserts.  I mean, there probably should be!  But this is irrelevant;
this whole function contains many such folio tests and the same problem
applies to all of them.  This patch doesn't make it worse.

> enforces a strict assertion:
> 
> VM_BUG_ON_PGFLAGS(PageTail(&folio->page))
> 
> If the page is concurrently reallocated as a tail page while
> is_page_hwpoison() executes, won't this crash the kernel on debug builds?
> 
> >  				 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);
> 
> This isn't a bug introduced by this patch, but does this lead to a
> double folio_put() and use-after-free for hugetlb folios?
> 
> If memory_failure() handles an in-use hugetlb folio, me_huge_page()
> might fail to dissolve it, meaning no extra poison reference is taken
> but the folio remains marked as hwpoisoned. If the folio is later
> unmapped and holds a single transient reference, unpoison_memory()
> will acquire a reference (ghp = 1) and perform the folio_put(folio)
> seen just below this reassignment.

I'm not an expert in the memory-poison field, but this also seems wrong.
Don't all hugetlb folios have a folio_mapping()?  And thus we'll never
take the dissolve path in me_huge_page().

At any rate, it says "not introduced by this patch", so I'm not going
to take any action.

> By reassigning p = &folio->page here, the subsequent call to
> TestClearPageHWPoison(p) will be tested on the head page and return
> true, triggering a second unconditional folio_put(folio). Does this
> underflow the transient pin and cause a use-after-free?
> 
> 
> This is a pre-existing issue, but does this same logic underflow the
> refcount for THP folios that previously failed to split?
> 
> If memory_failure() handles a THP and try_to_split_thp_page() fails, it
> explicitly drops the reference acquired via get_hwpoison_page(p), leaving
> the THP with no extra poison pin. However, TestSetPageHWPoison(p) was
> already called.
> 
> If the THP later reaches a state with a single transient reference
> and no mappings, unpoison_memory() acquires a reference (ghp = 1),
> calls folio_put(folio) once, and then TestClearPageHWPoison(p) clears
> the flag and returns true. This triggers the second folio_put(folio),
> dropping a non-existent poison pin.

I don't know, and I'm losing patience with the Sashiko rabbit holes.
This is all getting very far afield from the problem I actually want
to fix.

Re: [PATCH v5 01/12] memory-failure: Fix hardware poison check in unpoison_memory() again

[Andrew Morton]

On Mon, 27 Jul 2026 15:43:53 +0100 Matthew Wilcox <willy@infradead.org> wrote:

> > If the THP later reaches a state with a single transient reference
> > and no mappings, unpoison_memory() acquires a reference (ghp = 1),
> > calls folio_put(folio) once, and then TestClearPageHWPoison(p) clears
> > the flag and returns true. This triggers the second folio_put(folio),
> > dropping a non-existent poison pin.
> 
> I don't know, and I'm losing patience with the Sashiko rabbit holes.
> This is all getting very far afield from the problem I actually want
> to fix.

That's fair enough - you aren't a memory-failure maintainer.  If you
want to take a shot at the pre-existing things then great, but
otherwise then let's ensure that the relevant maintainers were cc'ed
and move on.

One relatively minor issue here is that if Sashiko's pre-exiting thing
is serious, we may decide to fix it with a cc:stable and such a fix
should be staged ahead of your series for backportability reasons.  If
we end up upstreaming these things in the "wrong" order then the
backportable-fix developers will be asked to prepare a backportable
version of their patch, which is a bit cumbersome, but not the end of the
world.

[PATCH v5 02/12] 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

Re: [PATCH v5 02/12] mm: Rename folio_contain_hwpoison_page() to folio_has_hwpoison_page()

[Matthew Wilcox]

Sashiko review:
> --- Patch [2]: [PATCH v5 02/12] mm: Rename folio_contain_hwpoison_page() to folio_has_hwpoison_page() ---
> commit 8fadf59bc3118e11dab2620f6cc376507c16b29a
> Author: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> mm: Rename folio_contain_hwpoison_page() to folio_has_hwpoison_page()
> 
> This is a better name for this predicate.  Also make the argument const
> to allow other callers to be made const.  No functional change.
> 
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > index 7223f6f4e2b40..4185a03a45cf7 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));
> >  }
> 
> This isn't a bug introduced by this patch, but can KSM trigger a machine check
> exception when scanning memory?

Good lord.  I renamed a function.  Which apparently causes Sashiko to
look for bugs in every caller

> Looking at cmp_and_merge_page() in mm/ksm.c, the KSM scanner initiates page
> hash calculation:
> 
> mm/ksm.c:cmp_and_merge_page() {
>     ...
>     checksum = calc_checksum(page);
>     ...
> }
> 
> which then maps and reads the page content:
> 
> mm/ksm.c:calc_checksum() {
>     ...
>     void *addr = kmap_local_page(page);
>     checksum = xxhash(addr, PAGE_SIZE, 0);
>     ...
> }
> 
> If a page becomes hardware-poisoned before KSM scans it, shouldn't there be a
> PageHWPoison(page) or folio_has_hwpoisoned_page(folio) check before the read
> to prevent a fatal MCE?
> 
> 
> This is a pre-existing issue, but does migration risk panicking on poisoned
> memory?

Yes, lots of things risk panicking on poisoned memory.  It's never been
a priority for Linux.

> During page migration, pages are passed to __migrate_folio() which copies the
> contents without validation:
> 
> mm/migrate.c:__migrate_folio() {
>     ...
>     rc = folio_mc_copy(dst, src);
>     if (unlikely(rc))
>         return rc;
>     ...
> }
> 
> This executes the page copy in folio_mc_copy():
> 
> mm/util.c:folio_mc_copy() {
>     ...
>     if (copy_mc_highpage(folio_page(dst, i), folio_page(src, i)))
>         return -EHWPOISON;
>     ...
> }
> 
> On architectures lacking copy_mc support, this falls back to copy_highpage().
> Without a prior folio_has_hwpoisoned_page(src) check, could migrating a
> poisoned page via mbind() or move_pages() read poisoned memory and trigger a
> kernel panic?
> 
> 
> This is a pre-existing issue, but does kill_accessing_process() return the
> wrong error code when a task lacks an mm?
> 
> In memory failure handling, if the task is exiting or is a kernel thread,
> p->mm is NULL:
> 
> mm/memory-failure.c:kill_accessing_process() {
>     ...
>     if (!p->mm)
>         return -EFAULT;
>     ...
> }
> 
> Since the memory_failure() API protocol requires returning 0 for a successfully
> recovered state (no user signal needed), does returning -EFAULT cause the
> architecture MCE handler, such as kill_me_maybe(), to erroneously conclude
> recovery failed? Could this trigger unnecessary warnings and incorrectly
> attempt to force a SIGBUS on the dying task?

Dunno, and I'm done with side-quests.  Somebody else can decide if this
is a real problem that needs to be fixed.

[PATCH v5 03/12] 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 v5 04/12] 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>
---
 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 v5 05/12] 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               | 14 +++++-----
 mm/memory-failure.c        | 56 +++++++++++++++++++++++++++-----------
 mm/rmap.c                  | 43 ++++++++++++++++++-----------
 7 files changed, 119 insertions(+), 50 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 cc8d98399913..aaac6e2af4c2 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))
@@ -1498,10 +1498,10 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
 	}
 
 	/*
-	 * Move PageHWPoison flag from head page to the raw error pages,
-	 * which makes any healthy subpages reusable.
+	 * 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);
 
 	VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
@@ -3998,7 +3998,7 @@ 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);
@@ -5809,7 +5809,7 @@ 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;
@@ -6318,7 +6318,7 @@ 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..9d245b4f2b8f 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() */
@@ -2730,8 +2753,8 @@ int unpoison_memory(unsigned long pfn)
 			count = folio_free_raw_hwp(folio, false);
 			if (count == 0)
 				goto unlock_mutex;
+			ret = hugetlb_clear_poison(folio);
 		}
-		ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
 	} else if (ghp < 0) {
 		if (ghp == -EHWPOISON) {
 			ret = put_page_back_buddy(p) ? 0 : -EBUSY;
@@ -2740,17 +2763,18 @@ 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;
 		}
-
+		folio_put(folio);
+		ret = hugetlb_clear_poison(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 v5 05/12] hugetlb: Use the has_hwpoisoned flag

[Matthew Wilcox]

Sashiko:
> --- Patch [5]: [PATCH v5 05/12] hugetlb: Use the has_hwpoisoned flag ---
> commit cca87d250a7a597186556cb9d897807edae0b82f
> Author: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> hugetlb: Use the has_hwpoisoned flag
> 
> This commit converts hugetlb to use the has_hwpoisoned flag to match
> other large folios. It introduces folio_test_huge_poison() for lockless
> checks to close a gap where a poisoned hugetlb folio could be observed
> without the hwpoison bit set during teardown.
> 
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > --- a/include/linux/page-flags.h
> > +++ b/include/linux/page-flags.h
> [ ... ]
> > @@ -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);
> > +}
> 
> This is a pre-existing issue, but does this logic fully close the race
> window?
> 
> The folio_test_huge_poison() function assumes the PGTY_hugetlb bits
> remain intact during teardown. However, __ClearPagehugetlb()
> unconditionally sets the entire page_type to UINT_MAX.
> 
> When __ClearPagehugetlb() is called, folio_test_huge_poison() will evaluate
> to false at the exact same moment folio_test_hugetlb() evaluates to false.
> Would this allow a concurrent is_page_hwpoison() check to miss the poison
> state?

Um, no?  Here's how is_page_hwpoison() looks:

static inline bool is_page_hwpoison(const struct page *page)
{
        const struct folio *folio;

        if (PageHWPoison(page))
                return true;
        folio = page_folio(page);
        if (folio_test_huge_poison(folio))
                return true;
        /* In case we raced with hugetlb transferring flags */
        return PageHWPoison(page);
}

We're relying on ordering; if we see a false folio_test_huge_poison(),
we recheck that the flag hasn't already been moved to the page.  Since
we always move the poison to the pages before clearing the page type,
I don't see how we can miss anything.

> > +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);
> > +}
> 
> Can this cause a data race on the page_type field?
> 
> In folio_clear_huge_poison(), the bitwise operation modifies the page_type
> field non-atomically. If unpoison_memory() calls this on a free hugetlb
> folio while a concurrent sysfs pool shrink calls __ClearPagehugetlb()
> under the hugetlb_lock, the UINT_MAX value could be overwritten with
> 0xFF7FFFFF.
> 
> Since unpoison_memory() relies on mf_mutex rather than hugetlb_lock,
> would this corrupted page_type trigger a VM_BUG_ON_PAGE in the buddy
> allocator when the page reaches free_pages_prepare()?

Hmm ... if we just move the hugetlb_clear_poison() call before the call
to folio_put(), that'll take care of this race, right?  Oh, but there's
two calls to folio_free_raw_hwp(), and the other one is when (ugh), we
don't have a reference to the folio.  So I think we wrap the whole thing
in hugetlb_lock to prevent this?

        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)
                                goto unlock_mutex;
                        ret = hugetlb_clear_poison(folio);
                } else {
                        ret = TestClearPageHWPoison(p) ? 0 : -EBUSY;
                }
                spin_unlock_irq(&hugetlb_lock);

(this also includes the fix to the problem discussed below)

> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> [ ... ]
> > @@ -1498,10 +1498,10 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
> >  	}
> >  
> >  	/*
> > -	 * Move PageHWPoison flag from head page to the raw error pages,
> > -	 * which makes any healthy subpages reusable.
> > +	 * 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);
> >  
> >  	VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
> 
> This is a pre-existing issue, but is there a risk of a double free in the
> hwpoison list teardown?
> 
> Both __update_and_free_hugetlb_folio() (via folio_clear_hugetlb_hwpoison())
> and unpoison_memory() can invoke __folio_free_raw_hwp() on the same folio
> concurrently. 
> 
> Looking at __folio_free_raw_hwp() in mm/memory-failure.c, it reads
> folio->hugetlb_hwpoison and sets it to NULL without any synchronization
> locks. If both threads read the pointer before either sets it to NULL,
> wouldn't they concurrently iterate the linked list and call kfree() on the
> same hwp_page elements?

I think that's right, but I also think it goes away later in this series
when hwp_page_lock serialises the calls to __folio_free_raw_hwp().

> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> [ ... ]
> > @@ -2730,8 +2753,8 @@ int unpoison_memory(unsigned long pfn)
> >  			count = folio_free_raw_hwp(folio, false);
> >  			if (count == 0)
> >  				goto unlock_mutex;
> > +			ret = hugetlb_clear_poison(folio);
> >  		}
> > -		ret = folio_test_clear_hwpoison(folio) ? 0 : -EBUSY;
> >  	} else if (ghp < 0) {
> >  		if (ghp == -EHWPOISON) {
> >  			ret = put_page_back_buddy(p) ? 0 : -EBUSY;
> > @@ -2740,17 +2763,18 @@ int unpoison_memory(unsigned long pfn)
> >  			unpoison_pr_info("%#lx: failed to grab page\n",
> >  					 pfn, &unpoison_rs);
> >  		}
> 
> Does this logic change drop the ability to unpoison free non-hugetlb pages?
> 
> The refactoring of the if (!ghp) block removed the fallback logic that
> handled non-hugetlb pages. If get_hwpoison_page() returns 0 for a free
> buddy page, execution enters the if (!ghp) block. 
> 
> Because folio_test_hugetlb(folio) is false, it does nothing, drops through
> the entire if/else chain, and returns -EBUSY. Could this leave free buddy
> pages permanently poisoned?

Oh, I see.  I hadn't realised that case was also being handled here.
I'll rework it.

[PATCH v5 06/12] 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      | 98 ++++++++++++++++++++++------------------
 4 files changed, 58 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 9d245b4f2b8f..e2f50b4aba82 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1808,63 +1808,57 @@ 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);
-
 	/*
-	 * 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))
 		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;
+	spin_lock_irqsave(&hwp_page_lock, flags);
+	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 +1899,8 @@ 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 +1910,23 @@ 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 +1935,20 @@ 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 +1963,11 @@ 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

Re: [PATCH v5 06/12] mm: Remove locking mf_mutex in is_raw_hwpoison_page_in_hugepage()

[Matthew Wilcox]

Sashiko:
> --- Patch [6]: [PATCH v5 06/12] mm: Remove locking mf_mutex in is_raw_hwpoison_page_in_hugepage() ---
> commit 5aafc5635bbbdae616864594ab6ced23fdde474f
> Author: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> mm: Remove locking mf_mutex in is_raw_hwpoison_page_in_hugepage()
> 
> This commit replaces mf_mutex with a new spinlock to protect the hwpoison
> list in hugetlb folios, preventing unexpected sleeping in predicate functions.
> It also renames the function to hugetlb_page_hwpoison and simplifies it to
> use a standard singly linked list.
> 
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index 9d245b4f2b8fe..e2f50b4aba822 100644
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> [ ... ]
> > +bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page)
> >  {
> [ ... ]
> >  	/*
> > -	 * 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))
> >  		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;
> > +	spin_lock_irqsave(&hwp_page_lock, flags);
> 
> This isn't a bug introduced by this patch, but is it possible for a race
> to occur if the unreliable flag is checked without holding the lock?
> 
> If CPU1 calls hugetlb_page_hwpoison() and checks the unreliable flag
> locklessly, it might read false.
> 
> Concurrently, CPU2 executing hugetlb_update_hwpoison() might fail to
> allocate a list entry, acquire hwp_page_lock, set the unreliable flag,
> and clear the hugetlb_hwpoison list:
> 
> hugetlb_update_hwpoison()
>     ...
>     p = kmalloc_obj(*p, GFP_ATOMIC);
>     if (p) {
>         ...
>     } else {
>         folio_set_hugetlb_raw_hwp_unreliable(folio);
>         __folio_free_raw_hwp(folio, false);
>     }
>     spin_unlock_irqrestore(&hwp_page_lock, flags);
> 
> CPU1 would then acquire hwp_page_lock, scan the now-empty list, and
> incorrectly conclude the page is safe. This could potentially allow
> poisoned memory to be accessed.
> 
> Would it be safer to check folio_test_hugetlb_raw_hwp_unreliable() inside
> the hwp_page_lock critical section?

Hm, yes, that's true.  I'll fold the fix into this patch:

@@ -1831,14 +1831,17 @@ bool hugetlb_page_hwpoison(const struct folio *folio, const struct page *page)
        if (!folio_test_has_hwpoisoned(folio))
                return false;

+       spin_lock_irqsave(&hwp_page_lock, flags);
+
        /*
         * 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;
+       }

-       spin_lock_irqsave(&hwp_page_lock, flags);
        for (p = folio->hugetlb_hwpoison; p; p = p->next) {
                if (page == p->page)
                        break;

> > +	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;
> >  }

[PATCH v5 07/12] 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 e2f50b4aba82..32f91935b210 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;
-
 	/*
 	 * When RawHwpUnreliable is set, kernel lost track of which pages
 	 * are HWPOISON. So return as if ALL pages are HWPOISONed.
@@ -1848,6 +1843,40 @@ 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 v5 08/12] 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 v5 09/12] 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 v5 10/12] 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 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 v5 11/12] 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

Re: [PATCH v5 11/12] filemap: Add support for authoritative mappings

[Matthew Wilcox]

Sashiko:
> --- Patch [11]: [PATCH v5 11/12] filemap: Add support for authoritative mappings ---
> commit 7b270a787d853107f7a64dd3127d799a28d3142e
> Author: Matthew Wilcox (Oracle) <willy@infradead.org>
> 
> filemap: Add support for authoritative mappings
> 
> 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.
> 
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 26a5f18121f90..5a8cc20e624e4 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;
> 
> Does returning 0 here cause an infinite loop in filemap_splice_read()?

As before, hugetlb doesn't use splice_read() so adding support would be
dead untestable code.  We'll add support here when we need it.

> > @@ -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;
> > +		}
> 
> Should filemap_fault() also be updated to handle authoritative mappings?

Eventually, if hugetlbfs is ever converted to use filemap_fault().
As above, it'd be dead code.


That's it for interesting Sashiko reviews.  I've omitted some which
are suplicates, either within this patch series or have been reported
against previous patch series.  Feels like we're close!

[PATCH v5 12/12] 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