linux-kernel - [PATCH v4 2/3] mm: Call arch_swap_restore() from unuse

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Message-Id: <20230523004312.1807357-3-pcc@google.com>
Date:   Mon, 22 May 2023 17:43:09 -0700
From:   Peter Collingbourne <pcc@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Peter Collingbourne <pcc@...gle.com>,
        "Qun-wei Lin (林群崴)" 
        <Qun-wei.Lin@...iatek.com>, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "surenb@...gle.com" <surenb@...gle.com>,
        "david@...hat.com" <david@...hat.com>,
        "Chinwen Chang (張錦文)" 
        <chinwen.chang@...iatek.com>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        "Kuan-Ying Lee (李冠穎)" 
        <Kuan-Ying.Lee@...iatek.com>,
        "Casper Li (李中榮)" 
        <casper.li@...iatek.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        vincenzo.frascino@....com,
        Alexandru Elisei <alexandru.elisei@....com>, will@...nel.org,
        eugenis@...gle.com, Steven Price <steven.price@....com>
Subject: [PATCH v4 2/3] mm: Call arch_swap_restore() from unuse_pte()

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@...gle.com>
Link: https://linux-review.googlesource.com/id/I68276653e612d64cde271ce1b5a99ae05d6bbc4f
Suggested-by: David Hildenbrand <david@...hat.com>
Acked-by: David Hildenbrand <david@...hat.com>
Acked-by: "Huang, Ying" <ying.huang@...el.com>
Reviewed-by: Steven Price <steven.price@....com>
Acked-by: Catalin Marinas <catalin.marinas@....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