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Mon, 01 Sep 2025 01:43:50 -0700 (PDT) Date: Mon, 1 Sep 2025 08:43:49 +0000 From: Wei Yang To: David Hildenbrand Cc: Wei Yang , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [Patch v2] selftests/mm: check content to see whether mremap corrupt data Message-ID: <20250901084349.imkxldwebqzgq3wd@master> Reply-To: Wei Yang References: <20250831022701.2595-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 78C7D1C000B X-Stat-Signature: pfs73git9edytiix6czfzqh3ya93pcu5 X-Rspam-User: X-HE-Tag: 1756716232-473 X-HE-Meta: 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 1s3oB1vK 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 01, 2025 at 09:22:44AM +0200, David Hildenbrand wrote: >On 31.08.25 04:27, Wei Yang wrote: > >Subject: "selftests/mm: verify page content after remapping PMD through PTEs" > >> After mremap(), add a check on content to see whether mremap corrupt >> data. >> >> Signed-off-by: Wei Yang >> >> --- >> v2: add check on content instead of just test backed folio > >I'm confused, don't we have that exact check later in the function? > >Your v1 might have been better, unless I am missing something. > Maybe I should insist a little. >> --- >> tools/testing/selftests/mm/split_huge_page_test.c | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c >> index 10ae65ea032f..229b6dcabece 100644 >> --- a/tools/testing/selftests/mm/split_huge_page_test.c >> +++ b/tools/testing/selftests/mm/split_huge_page_test.c >> @@ -423,10 +423,14 @@ static void split_pte_mapped_thp(void) >> /* smap does not show THPs after mremap, use kpageflags instead */ >> thp_size = 0; >> - for (i = 0; i < pagesize * 4; i++) >> + for (i = 0; i < pagesize * 4; i++) { >> + if (pte_mapped[i] != (char)i) >> + ksft_exit_fail_msg("%ld byte corrupted\n", i); >> + >> if (i % pagesize == 0 && >> is_backed_by_folio(&pte_mapped[i], pmd_order, pagemap_fd, kpageflags_fd)) >> thp_size++; >> + } >> if (thp_size != 4) >> ksft_exit_fail_msg("Some THPs are missing during mremap\n"); > >I'm a bit confused with this test in general. > >We do a > >pte_mapped = mremap(one_page, pagesize, pagesize, MREMAP_MAYMOVE); > >which I read as a "NOP". > >Questions > >(a) Will this actually do anything? Also, maybe it does now, but can't the >kernel just optimize that out in the future? > >(b) Is it even guaranteed that we can access > pagesize afterwards? I mean, >we specify MREMAP_MAYMOVE. > To be honest, I am not fully understand the operations here. > >I would suggest to just use mprotect/madvise to pte-map a PMD-THP. > >This is, of course, independent of this patch. > >-- >Cheers > >David / dhildenb -- Wei Yang Help you, Help me