[PATCH v4 0/3] mm: Fix bug affecting swapping in MTE tagged pages

[PATCH v4 0/3] mm: Fix bug affecting swapping in MTE tagged pages

[Peter Collingbourne]

This patch series reworks the logic that handles swapping in page
metadata to fix a reported bug [1] where metadata can sometimes not
be swapped in correctly after commit c145e0b47c77 ("mm: streamline COW
logic in do_swap_page()").

- Patch 1 fixes the bug itself, but still requires architectures
  to restore metadata in both arch_swap_restore() and set_pte_at().

- Patch 2 makes it so that architectures only need to restore metadata
  in arch_swap_restore().

- Patch 3 changes arm64 to remove support for restoring metadata
  in set_pte_at().

[1] https://lore.kernel.org/all/5050805753ac469e8d727c797c2218a9d780d434.camel@mediatek.com/

v4:
- Rebased onto v6.4-rc3
- Reverted change to arch/arm64/mm/mteswap.c; this change was not
  valid because swapcache pages can have arch_swap_restore() called
  on them multiple times

v3:
- Added patch to call arch_swap_restore() from unuse_pte()
- Rebased onto arm64/for-next/fixes

v2:
- Call arch_swap_restore() directly instead of via arch_do_swap_page()

Peter Collingbourne (3):
  mm: Call arch_swap_restore() from do_swap_page()
  mm: Call arch_swap_restore() from unuse_pte()
  arm64: mte: Simplify swap tag restoration logic

 arch/arm64/include/asm/mte.h     |  4 ++--
 arch/arm64/include/asm/pgtable.h | 14 ++----------
 arch/arm64/kernel/mte.c          | 37 ++++++--------------------------
 mm/memory.c                      |  7 ++++++
 mm/swapfile.c                    |  7 ++++++
 5 files changed, 25 insertions(+), 44 deletions(-)

-- 
2.40.1.698.g37aff9b760-goog

[PATCH v4 1/3] mm: Call arch_swap_restore() from do_swap_page()

[Peter Collingbourne]

Commit c145e0b47c77 ("mm: streamline COW logic in do_swap_page()") moved
the call to swap_free() before the call to set_pte_at(), which meant that
the MTE tags could end up being freed before set_pte_at() had a chance
to restore them. Fix it by adding a call to the arch_swap_restore() hook
before the call to swap_free().

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/I6470efa669e8bd2f841049b8c61020c510678965
Cc: <stable@vger.kernel.org> # 6.1
Fixes: c145e0b47c77 ("mm: streamline COW logic in do_swap_page()")
Reported-by: Qun-wei Lin (林群崴) <Qun-wei.Lin@mediatek.com>
Closes: https://lore.kernel.org/all/5050805753ac469e8d727c797c2218a9d780d434.camel@mediatek.com/
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
---
v2:
- Call arch_swap_restore() directly instead of via arch_do_swap_page()

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

diff --git a/mm/memory.c b/mm/memory.c
index f69fbc251198..fc25764016b3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3932,6 +3932,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 		}
 	}
 
+	/*
+	 * Some architectures may have to restore extra metadata to the page
+	 * when reading from swap. This metadata may be indexed by swap entry
+	 * so this must be called before swap_free().
+	 */
+	arch_swap_restore(entry, folio);
+
 	/*
 	 * Remove the swap entry and conditionally try to free up the swapcache.
 	 * We're already holding a reference on the page but haven't mapped it
-- 
2.40.1.698.g37aff9b760-goog

[PATCH v4 2/3] mm: Call arch_swap_restore() from unuse_pte()

[Peter Collingbourne]

We would like to move away from requiring architectures to restore
metadata from swap in the set_pte_at() implementation, as this is not only
error-prone but adds complexity to the arch-specific code. This requires
us to call arch_swap_restore() before calling swap_free() whenever pages
are restored from swap. We are currently doing so everywhere except in
unuse_pte(); do so there as well.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/I68276653e612d64cde271ce1b5a99ae05d6bbc4f
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
---
 mm/swapfile.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 274bbf797480..e9843fadecd6 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1794,6 +1794,13 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 		goto setpte;
 	}
 
+	/*
+	 * Some architectures may have to restore extra metadata to the page
+	 * when reading from swap. This metadata may be indexed by swap entry
+	 * so this must be called before swap_free().
+	 */
+	arch_swap_restore(entry, page_folio(page));
+
 	/* See do_swap_page() */
 	BUG_ON(!PageAnon(page) && PageMappedToDisk(page));
 	BUG_ON(PageAnon(page) && PageAnonExclusive(page));
-- 
2.40.1.698.g37aff9b760-goog

[PATCH v4 3/3] arm64: mte: Simplify swap tag restoration logic

[Peter Collingbourne]

As a result of the previous two patches, there are no circumstances
in which a swapped-in page is installed in a page table without first
having arch_swap_restore() called on it. Therefore, we no longer need
the logic in set_pte_at() that restores the tags, so remove it.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/I8ad54476f3b2d0144ccd8ce0c1d7a2963e5ff6f3
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
v4:
- Rebased onto v6.4-rc3
- Reverted change to arch/arm64/mm/mteswap.c; this change was not
  valid because swapcache pages can have arch_swap_restore() called
  on them multiple times

v3:
- Rebased onto arm64/for-next/fixes, which already has a fix
  for the issue previously tagged, therefore removed Fixes:
  tag

 arch/arm64/include/asm/mte.h     |  4 ++--
 arch/arm64/include/asm/pgtable.h | 14 ++----------
 arch/arm64/kernel/mte.c          | 37 ++++++--------------------------
 3 files changed, 11 insertions(+), 44 deletions(-)

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index c028afb1cd0b..4cedbaa16f41 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -90,7 +90,7 @@ static inline bool try_page_mte_tagging(struct page *page)
 }
 
 void mte_zero_clear_page_tags(void *addr);
-void mte_sync_tags(pte_t old_pte, pte_t pte);
+void mte_sync_tags(pte_t pte);
 void mte_copy_page_tags(void *kto, const void *kfrom);
 void mte_thread_init_user(void);
 void mte_thread_switch(struct task_struct *next);
@@ -122,7 +122,7 @@ static inline bool try_page_mte_tagging(struct page *page)
 static inline void mte_zero_clear_page_tags(void *addr)
 {
 }
-static inline void mte_sync_tags(pte_t old_pte, pte_t pte)
+static inline void mte_sync_tags(pte_t pte)
 {
 }
 static inline void mte_copy_page_tags(void *kto, const void *kfrom)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 0bd18de9fd97..e8a252e62b12 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -337,18 +337,8 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
 	 * don't expose tags (instruction fetches don't check tags).
 	 */
 	if (system_supports_mte() && pte_access_permitted(pte, false) &&
-	    !pte_special(pte)) {
-		pte_t old_pte = READ_ONCE(*ptep);
-		/*
-		 * We only need to synchronise if the new PTE has tags enabled
-		 * or if swapping in (in which case another mapping may have
-		 * set tags in the past even if this PTE isn't tagged).
-		 * (!pte_none() && !pte_present()) is an open coded version of
-		 * is_swap_pte()
-		 */
-		if (pte_tagged(pte) || (!pte_none(old_pte) && !pte_present(old_pte)))
-			mte_sync_tags(old_pte, pte);
-	}
+	    !pte_special(pte) && pte_tagged(pte))
+		mte_sync_tags(pte);
 
 	__check_safe_pte_update(mm, ptep, pte);
 
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 7e89968bd282..c40728046fed 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -35,41 +35,18 @@ DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
 EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode);
 #endif
 
-static void mte_sync_page_tags(struct page *page, pte_t old_pte,
-			       bool check_swap, bool pte_is_tagged)
-{
-	if (check_swap && is_swap_pte(old_pte)) {
-		swp_entry_t entry = pte_to_swp_entry(old_pte);
-
-		if (!non_swap_entry(entry))
-			mte_restore_tags(entry, page);
-	}
-
-	if (!pte_is_tagged)
-		return;
-
-	if (try_page_mte_tagging(page)) {
-		mte_clear_page_tags(page_address(page));
-		set_page_mte_tagged(page);
-	}
-}
-
-void mte_sync_tags(pte_t old_pte, pte_t pte)
+void mte_sync_tags(pte_t pte)
 {
 	struct page *page = pte_page(pte);
 	long i, nr_pages = compound_nr(page);
-	bool check_swap = nr_pages == 1;
-	bool pte_is_tagged = pte_tagged(pte);
-
-	/* Early out if there's nothing to do */
-	if (!check_swap && !pte_is_tagged)
-		return;
 
 	/* if PG_mte_tagged is set, tags have already been initialised */
-	for (i = 0; i < nr_pages; i++, page++)
-		if (!page_mte_tagged(page))
-			mte_sync_page_tags(page, old_pte, check_swap,
-					   pte_is_tagged);
+	for (i = 0; i < nr_pages; i++, page++) {
+		if (try_page_mte_tagging(page)) {
+			mte_clear_page_tags(page_address(page));
+			set_page_mte_tagged(page);
+		}
+	}
 
 	/* ensure the tags are visible before the PTE is set */
 	smp_wmb();
-- 
2.40.1.698.g37aff9b760-goog

Re: [PATCH v4 1/3] mm: Call arch_swap_restore() from do_swap_page()

[Catalin Marinas]

On Mon, Jun 05, 2023 at 10:41:12AM -0700, Peter Collingbourne wrote:
> On Mon, Jun 5, 2023 at 7:06 AM Will Deacon <will@kernel.org> wrote:
> > On Mon, May 22, 2023 at 05:43:08PM -0700, Peter Collingbourne wrote:
> > > Commit c145e0b47c77 ("mm: streamline COW logic in do_swap_page()") moved
> > > the call to swap_free() before the call to set_pte_at(), which meant that
> > > the MTE tags could end up being freed before set_pte_at() had a chance
> > > to restore them. Fix it by adding a call to the arch_swap_restore() hook
> > > before the call to swap_free().
> > >
> > > Signed-off-by: Peter Collingbourne <pcc@google.com>
> > > Link: https://linux-review.googlesource.com/id/I6470efa669e8bd2f841049b8c61020c510678965
> > > Cc: <stable@vger.kernel.org> # 6.1
> > > Fixes: c145e0b47c77 ("mm: streamline COW logic in do_swap_page()")
> > > Reported-by: Qun-wei Lin (林群崴) <Qun-wei.Lin@mediatek.com>
> > > Closes: https://lore.kernel.org/all/5050805753ac469e8d727c797c2218a9d780d434.camel@mediatek.com/
> > > Acked-by: David Hildenbrand <david@redhat.com>
> > > Acked-by: "Huang, Ying" <ying.huang@intel.com>
> > > Reviewed-by: Steven Price <steven.price@arm.com>
> > > Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> > > ---
> > > v2:
> > > - Call arch_swap_restore() directly instead of via arch_do_swap_page()
> > >
> > >  mm/memory.c | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > >
> > > diff --git a/mm/memory.c b/mm/memory.c
> > > index f69fbc251198..fc25764016b3 100644
> > > --- a/mm/memory.c
> > > +++ b/mm/memory.c
> > > @@ -3932,6 +3932,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
> > >               }
> > >       }
> > >
> > > +     /*
> > > +      * Some architectures may have to restore extra metadata to the page
> > > +      * when reading from swap. This metadata may be indexed by swap entry
> > > +      * so this must be called before swap_free().
> > > +      */
> > > +     arch_swap_restore(entry, folio);
> > > +
> > >       /*
> > >        * Remove the swap entry and conditionally try to free up the swapcache.
> > >        * We're already holding a reference on the page but haven't mapped it
> >
> > It looks like the intention is for this patch to land in 6.4, whereas the
> > other two in the series could go in later, right? If so, I was expecting
> > Andrew to pick this one up but he's not actually on CC. I've added him now,
> > but you may want to send this as a separate fix so it's obvious what needs
> > picking up for this cycle.
> 
> I was expecting that this whole series could be picked up in mm. There
> was a previous attempt to apply v3 of this series to mm, but that
> failed because a dependent patch (commit c4c597f1b367 ("arm64: mte: Do
> not set PG_mte_tagged if tags were not initialized")) hadn't been
> merged into Linus's master branch yet. The series should be good to go
> in now that that patch has been merged.

Did this series fall through the cracks? I can't see it in linux-next
(or maybe my grep'ing failed). The commit mentioned above is in 6.4-rc3
AFAICT. Unfortunately Andrew was not cc'ed on the initial post, Will
added him later, so he likely missed it. For reference, the series is
here:

https://lore.kernel.org/r/20230523004312.1807357-1-pcc@google.com/

Andrew, what's your preference for this series? I'd like at least the
first patch to go into 6.5 as a fix. The second patch seems to be fairly
low risk and I'm happy for the third arm64 patch/cleanup to go in
6.5-rc1 (but it depends on the second patch). If you prefer, I can pick
them up and send a pull request to Linus next week before -rc1.
Otherwise you (or I) can queue the first patch and leave the other two
for 6.6.

Thanks.

-- 
Catalin

Re: [PATCH v4 1/3] mm: Call arch_swap_restore() from do_swap_page()

[Andrew Morton]

On Thu, 29 Jun 2023 10:57:14 +0100 Catalin Marinas <catalin.marinas@arm.com> wrote:

> Andrew, what's your preference for this series? I'd like at least the
> first patch to go into 6.5 as a fix. The second patch seems to be fairly
> low risk and I'm happy for the third arm64 patch/cleanup to go in
> 6.5-rc1 (but it depends on the second patch). If you prefer, I can pick
> them up and send a pull request to Linus next week before -rc1.
> Otherwise you (or I) can queue the first patch and leave the other two
> for 6.6.

Thanks.  I queued [1/3] for 6.5-rcX with a cc:stable.  And I queued
[2/3] and [3/3] for 6.6-rc1.

If you wish to grab any/all of these then please do so - Stephen
will tell us of the duplicate and I'll drop the mm-git copy.

Re: [PATCH v4 1/3] mm: Call arch_swap_restore() from do_swap_page()

[Catalin Marinas]

On Sun, Jul 02, 2023 at 12:38:21PM -0700, Andrew Morton wrote:
> On Thu, 29 Jun 2023 10:57:14 +0100 Catalin Marinas <catalin.marinas@arm.com> wrote:
> > Andrew, what's your preference for this series? I'd like at least the
> > first patch to go into 6.5 as a fix. The second patch seems to be fairly
> > low risk and I'm happy for the third arm64 patch/cleanup to go in
> > 6.5-rc1 (but it depends on the second patch). If you prefer, I can pick
> > them up and send a pull request to Linus next week before -rc1.
> > Otherwise you (or I) can queue the first patch and leave the other two
> > for 6.6.
> 
> Thanks.  I queued [1/3] for 6.5-rcX with a cc:stable.  And I queued
> [2/3] and [3/3] for 6.6-rc1.
> 
> If you wish to grab any/all of these then please do so - Stephen
> will tell us of the duplicate and I'll drop the mm-git copy.

That's great, thanks. We'll let you know if there are any conflicts
during the 6.6 preparation.

-- 
Catalin