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Date:   Fri, 12 May 2023 16:57:51 -0700
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Subject: [PATCH 2/3] mm: Call arch_swap_restore() from arch_do_swap_page() and
 deprecate the latter
From:   Peter Collingbourne <pcc@google.com>
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Peter Collingbourne <pcc@google.com>,
        "=?UTF-8?q?Qun-wei=20Lin=20=28=E6=9E=97=E7=BE=A4=E5=B4=B4=29?=" 
        <Qun-wei.Lin@mediatek.com>, linux-arm-kernel@lists.infradead.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        "surenb@google.com" <surenb@google.com>,
        "david@redhat.com" <david@redhat.com>,
        "=?UTF-8?q?Chinwen=20Chang=20=28=E5=BC=B5=E9=8C=A6=E6=96=87=29?=" 
        <chinwen.chang@mediatek.com>,
        "kasan-dev@googlegroups.com" <kasan-dev@googlegroups.com>,
        "=?UTF-8?q?Kuan-Ying=20Lee=20=28=E6=9D=8E=E5=86=A0=E7=A9=8E=29?=" 
        <Kuan-Ying.Lee@mediatek.com>,
        "=?UTF-8?q?Casper=20Li=20=28=E6=9D=8E=E4=B8=AD=E6=A6=AE=29?=" 
        <casper.li@mediatek.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        vincenzo.frascino@arm.com,
        Alexandru Elisei <alexandru.elisei@arm.com>, will@kernel.org,
        eugenis@google.com, Steven Price <steven.price@arm.com>,
        stable@vger.kernel.org
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Precedence: bulk

The previous patch made it possible for MTE to restore tags before they
are freed by hooking arch_do_swap_page().

However, the arch_do_swap_page() hook API is incompatible with swap
restoration in circumstances where we do not have an mm or a vma,
such as swapoff with swapped out shmem, and I expect that ADI will
currently fail to restore tags in these circumstances. This implies that
arch-specific metadata stores ought to be indexed by swap index, as MTE
does, rather than by mm and vma, as ADI does, and we should discourage
hooking arch_do_swap_page(), preferring to hook arch_swap_restore()
instead, as MTE already does.

Therefore, instead of directly hooking arch_do_swap_page() for
MTE, deprecate that hook, change its default implementation to call
arch_swap_restore() and rely on the existing implementation of the latter
for MTE.

Fixes: c145e0b47c77 ("mm: streamline COW logic in do_swap_page()")
Link: https://linux-review.googlesource.com/id/Id2f1ad76eaf606ae210e1d2dd0b=
7fe287e5f7d87
Signed-off-by: Peter Collingbourne <pcc@google.com>
Reported-by: Qun-wei Lin (=E6=9E=97=E7=BE=A4=E5=B4=B4) <Qun-wei.Lin@mediate=
k.com>
Link: https://lore.kernel.org/all/5050805753ac469e8d727c797c2218a9d780d434.=
camel@mediatek.com/
Cc: <stable@vger.kernel.org> # 6.1
---
 include/linux/pgtable.h | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index c63cd44777ec..fc0259cf60fb 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -740,6 +740,12 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
 	set_pgd(pgdp, pgd); \
 })
=20
+#ifndef __HAVE_ARCH_SWAP_RESTORE
+static inline void arch_swap_restore(swp_entry_t entry, struct folio *foli=
o)
+{
+}
+#endif
+
 #ifndef __HAVE_ARCH_DO_SWAP_PAGE
 /*
  * Some architectures support metadata associated with a page. When a
@@ -748,14 +754,14 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
  * processors support an ADI (Application Data Integrity) tag for the
  * page as metadata for the page. arch_do_swap_page() can restore this
  * metadata when a page is swapped back in.
+ *
+ * This hook is deprecated. Architectures should hook arch_swap_restore()
+ * instead, because this hook is not called on all code paths that can
+ * swap in a page, particularly those where mm and vma are not available
+ * (e.g. swapoff for shmem pages).
  */
-static inline void arch_do_swap_page(struct mm_struct *mm,
-				     struct vm_area_struct *vma,
-				     unsigned long addr,
-				     pte_t pte, pte_t oldpte)
-{
-
-}
+#define arch_do_swap_page(mm, vma, addr, pte, oldpte) \
+	arch_swap_restore(pte_to_swp_entry(oldpte), page_folio(pte_page(pte)))
 #endif
=20
 #ifndef __HAVE_ARCH_UNMAP_ONE
@@ -798,12 +804,6 @@ static inline void arch_swap_invalidate_area(int type)
 }
 #endif
=20
-#ifndef __HAVE_ARCH_SWAP_RESTORE
-static inline void arch_swap_restore(swp_entry_t entry, struct folio *foli=
o)
-{
-}
-#endif
-
 #ifndef __HAVE_ARCH_PGD_OFFSET_GATE
 #define pgd_offset_gate(mm, addr)	pgd_offset(mm, addr)
 #endif
--=20
2.40.1.606.ga4b1b128d6-goog