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Mon, 01 Sep 2025 01:34:33 -0700 (PDT) Received: from smtpclient.apple ([2400:d320:2231:7720::1]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-24903724c62sm95960595ad.34.2025.09.01.01.34.28 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 01 Sep 2025 01:34:33 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.700.81\)) Subject: Re: [Patch v2] selftests/mm: check content to see whether mremap corrupt data From: wang lian In-Reply-To: Date: Mon, 1 Sep 2025 16:34:14 +0800 Cc: akpm@linux-foundation.org, baolin.wang@linux.alibaba.com, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, richard.weiyang@gmail.com, ziy@nvidia.com Content-Transfer-Encoding: quoted-printable Message-Id: <604B12DD-4BF7-481D-8E09-0D97C8843639@gmail.com> References: <20250901081109.52460-1-lianux.mm@gmail.com> To: David Hildenbrand X-Mailer: Apple Mail (2.3826.700.81) X-Rspamd-Queue-Id: 18B5840004 X-Rspam-User: X-Stat-Signature: dz9tdu7r7kskqzf6r9n7ucbzqn3uazgh X-Rspamd-Server: rspam09 X-HE-Tag: 1756715674-980014 X-HE-Meta: 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 Qs3Qlst4 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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 Sep 1, 2025, at 16:16, David Hildenbrand wrote: >=20 > On 01.09.25 10:11, wang lian wrote: >>> 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. >> Hi David, >> Perhaps you missed this in the v1 feedback: >> = https://lore.kernel.org/linux-mm/E0C570E7-C4CD-4E41-9590-DDB64757CA2C@nvid= ia.com/ ? >=20 > We have: >=20 > /* smap does not show THPs after mremap, use kpageflags instead = */ > thp_size =3D 0; > for (i =3D 0; i < pagesize * 4; i++) { > if (pte_mapped[i] !=3D (char)i) > ksft_exit_fail_msg("%ld byte corrupted\n", i); >=20 > if (i % pagesize =3D=3D 0 && > !is_backed_by_folio(&pte_mapped[i], 0, pagemap_fd, = kpageflags_fd)) > thp_size++; > } >=20 > Sure, it's after the split, but if mremap would have corrupted the = pages, surely > it would still be corrupt after the mremap+split. Yes, so I think it is correct to add this check in mremap. The check after splitting already exists >=20 > --=20 > Cheers >=20 > David / dhildenb >=20 Best regards, wang lian