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Date:   Tue, 16 May 2023 19:21:12 -0700
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Subject: [PATCH v3 2/3] mm: Call arch_swap_restore() from unuse_pte()
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>,
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        <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>
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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
---
 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));
-- 
2.40.1.606.ga4b1b128d6-goog