linux-kernel - [PATCH v4 12/14] fs/proc: Support COW PTE with clear_refs

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Message-Id: <20230207035139.272707-13-shiyn.lin@gmail.com>
Date:   Tue,  7 Feb 2023 11:51:37 +0800
From:   Chih-En Lin <shiyn.lin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        David Hildenbrand <david@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
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        John Hubbard <jhubbard@...dia.com>,
        Nadav Amit <namit@...are.com>, Barry Song <baohua@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
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        Fenghua Yu <fenghua.yu@...el.com>,
        Andrei Vagin <avagin@...il.com>,
        Barret Rhoden <brho@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Alexey Gladkov <legion@...nel.org>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Dinglan Peng <peng301@...due.edu>,
        Pedro Fonseca <pfonseca@...due.edu>,
        Jim Huang <jserv@...s.ncku.edu.tw>,
        Huichun Feng <foxhoundsk.tw@...il.com>,
        Chih-En Lin <shiyn.lin@...il.com>
Subject: [PATCH v4 12/14] fs/proc: Support COW PTE with clear_refs_write

Before clearing the entry in COW-ed PTE, break COW PTE first.

Signed-off-by: Chih-En Lin <shiyn.lin@...il.com>
---
 fs/proc/task_mmu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index af1c49ae11b1..94958422aede 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1196,6 +1196,11 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
 	if (pmd_trans_unstable(pmd))
 		return 0;
 
+	/* Only break COW when we modify the soft-dirty bit. */
+	if (cp->type == CLEAR_REFS_SOFT_DIRTY &&
+	    break_cow_pte(vma, pmd, addr))
+		return 0;
+
 	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 	for (; addr != end; pte++, addr += PAGE_SIZE) {
 		ptent = *pte;
-- 
2.34.1