linux-kernel - [PATCH v2 2/3] mm/swapfile: Fix lost swap bits in unuse

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Date:   Thu, 21 Apr 2022 20:53:47 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <willy@...radead.org>, <vbabka@...e.cz>, <dhowells@...hat.com>,
        <neilb@...e.de>, <david@...hat.com>, <apopple@...dia.com>,
        <surenb@...gle.com>, <minchan@...nel.org>, <peterx@...hat.com>,
        <sfr@...b.auug.org.au>, <naoya.horiguchi@....com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH v2 2/3] mm/swapfile: Fix lost swap bits in unuse_pte()

This is observed by code review only but not any real report.

When we turn off swapping we could have lost the bits stored in the swap
ptes. The new rmap-exclusive bit is fine since that turned into a page
flag, but not for soft-dirty and uffd-wp. Add them.

Suggested-by: Peter Xu <peterx@...hat.com>
Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 mm/swapfile.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 95b63f69f388..332ccfc76142 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1783,7 +1783,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 {
 	struct page *swapcache;
 	spinlock_t *ptl;
-	pte_t *pte;
+	pte_t *pte, new_pte;
 	int ret = 1;
 
 	swapcache = page;
@@ -1832,8 +1832,14 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 		page_add_new_anon_rmap(page, vma, addr);
 		lru_cache_add_inactive_or_unevictable(page, vma);
 	}
-	set_pte_at(vma->vm_mm, addr, pte,
-		   pte_mkold(mk_pte(page, vma->vm_page_prot)));
+	new_pte = pte_mkold(mk_pte(page, vma->vm_page_prot));
+	if (pte_swp_soft_dirty(*pte))
+		new_pte = pte_mksoft_dirty(new_pte);
+	if (pte_swp_uffd_wp(*pte)) {
+		new_pte = pte_mkuffd_wp(new_pte);
+		new_pte = pte_wrprotect(new_pte);
+	}
+	set_pte_at(vma->vm_mm, addr, pte, new_pte);
 	swap_free(entry);
 out:
 	pte_unmap_unlock(pte, ptl);
-- 
2.23.0