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Date:   Fri, 14 Apr 2023 22:23:34 +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>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        John Hubbard <jhubbard@...dia.com>,
        Nadav Amit <namit@...are.com>, Barry Song <baohua@...nel.org>,
        Pasha Tatashin <pasha.tatashin@...een.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Yu Zhao <yuzhao@...gle.com>,
        Steven Barrett <steven@...uorix.net>,
        Juergen Gross <jgross@...e.com>, Peter Xu <peterx@...hat.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Tong Tiangen <tongtiangen@...wei.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Yang Shi <shy828301@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Alex Sierra <alex.sierra@....com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Li kunyu <kunyu@...china.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Joey Gouly <joey.gouly@....com>,
        Chih-En Lin <shiyn.lin@...il.com>,
        Michal Hocko <mhocko@...e.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        "Zach O'Keefe" <zokeefe@...gle.com>,
        Gautam Menghani <gautammenghani201@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Brown <broonie@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andrei Vagin <avagin@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...nel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexey Gladkov <legion@...nel.org>, x86@...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>
Subject: [PATCH v5 10/17] mm/gup: Trigger break COW PTE before calling follow_pfn_pte()

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

Signed-off-by: Chih-En Lin <shiyn.lin@...il.com>
---
 mm/gup.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index eab18ba045db..325424c02ca6 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -544,7 +544,8 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
 			 (FOLL_PIN | FOLL_GET)))
 		return ERR_PTR(-EINVAL);
-	if (unlikely(pmd_bad(*pmd)))
+	/* COW-ed PTE has write protection which can trigger pmd_bad(). */
+	if (unlikely(pmd_write(*pmd) && pmd_bad(*pmd)))
 		return no_page_table(vma, flags);
 
 	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
@@ -587,6 +588,11 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 		if (is_zero_pfn(pte_pfn(pte))) {
 			page = pte_page(pte);
 		} else {
+			if (test_bit(MMF_COW_PTE, &mm->flags) &&
+			    !pmd_write(*pmd)) {
+				page = ERR_PTR(-EMLINK);
+				goto out;
+			}
 			ret = follow_pfn_pte(vma, address, ptep, flags);
 			page = ERR_PTR(ret);
 			goto out;
-- 
2.34.1

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