linux-kernel - [PATCH v3 08/14] mm/gup: Break COW PTE in follow_pfn

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Date:   Tue, 20 Dec 2022 15:27:37 +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>,
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        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
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        Fenghua Yu <fenghua.yu@...el.com>,
        Barret Rhoden <brho@...gle.com>,
        Davidlohr Bueso <dave@...olabs.net>,
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        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 v3 08/14] mm/gup: Break COW PTE in follow_pfn_pte()

In most of cases, GUP will not modify the page table,
excluding follow_pfn_pte(). To deal with COW PTE, break
COW PTE in follow_pfn_pte().

Signed-off-by: Chih-En Lin <shiyn.lin@...il.com>
---
 mm/gup.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index fe195d47de74a..cd72010ba0e6d 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -476,6 +476,8 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
 		entry = pte_mkyoung(entry);
 
 		if (!pte_same(*pte, entry)) {
+			if (break_cow_pte(vma, NULL, address) < 0)
+				return -ENOMEM;
 			set_pte_at(vma->vm_mm, address, pte, entry);
 			update_mmu_cache(vma, address, pte);
 		}
-- 
2.37.3