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AJvYcCWj3cnwPQ+bLx8DZbHL2pgYuBSM65uUnwV/gbHAw2gsNL+7PaFqUf+lY+UV1b5UdAUy0WEYgflrZSpVsWx9EYPlioc= X-Gm-Message-State: AOJu0YzhVyyDJse8kfYKEGChW2LxIOlddO63v0h2pdS+PWlaQ7VZCwEM yMbab3sGvCmmtsN4YXJ+1CV+4+2I4SmneNLHv98+mosJeyumrwxgFJ0zPsAyiARHdx0QYdg1g1G HtZeVGFr7waU0sJC8Y5QyhEErO9s= X-Google-Smtp-Source: AGHT+IGERW1IeD22ep/7ZxNjLmYxShr7IfSgZW0Lwc1Ew0CHS2TcDv1xLiHW7OYMeA/oZxsrKaAuo11kQGqHXiE0so4= X-Received: by 2002:a81:6cc7:0:b0:608:3c43:9186 with SMTP id h190-20020a816cc7000000b006083c439186mr1571872ywc.45.1709023534709; Tue, 27 Feb 2024 00:45:34 -0800 (PST) MIME-Version: 1.0 References: <20240227070418.62292-1-ioworker0@gmail.com> <90471b2f-826e-4275-a9a3-ec673c3e6af8@redhat.com> <2aa8b0f0-4fd4-469a-ba72-82fe01d37f15@redhat.com> In-Reply-To: <2aa8b0f0-4fd4-469a-ba72-82fe01d37f15@redhat.com> From: Lance Yang Date: Tue, 27 Feb 2024 16:45:23 +0800 Message-ID: Subject: Re: [PATCH 1/1] mm/memory: Fix boundary check for next PFN in folio_pte_batch() To: David Hildenbrand Cc: akpm@linux-foundation.org, ryan.roberts@arm.com, 21cnbao@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 1F9E18000B X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: gszu9z87p6d5dmxek1txomywj3w61r5w X-HE-Tag: 1709023536-391816 X-HE-Meta: U2FsdGVkX1+j5oWAAj4gOmVf/2lP04Z1LwoK0MExhug7Qjs3NkIAGRxE/GfisG2QQ3Pt0R4c9LhUlf67ypVWwiNZcdL9FcQU+Y9M5QCCfiXbzCCvc2XJA9kErvzFG4vf1iRDYBhn9hOCSVZ+PlYq+x150Sgb2arEWtDvB3UHvKVRxJ7zZ/zl3mV7WA3RZd0Cg5vgwvFEOi4ohVR39oJn2m3GMLaipD4rxXjS3DXZXgPlx6zHlyKAutT1fqzNEd5dwXW+3PrWvL7HqZhDuJ5vwgRPy0xpEp/cPsMyBwZz3fy3pW2iki6lDI1WAZN9z4Z36dHmpJTVtY8iLvsn6PHQXSSN/2OaEaPf58KXX6eUZg+f8mLaTl90qS5rGShvrpCwIyssk0+1ETrpobtGrUaOAHyCmiFVomx569ZIVwCb4WD/smCa4vRxpWuuzzBA4pUUrfcfSahuac4I6iZsHQu6QRdTRj18/a4hs3I1W0wb5UjEs5pPzIMTSAWpoVTbXBYbYNY6g8RLnN+F0zSoBtcFp5cKd7O9Hdk887NxVXxGQuN+FXhxycmajy0nsI/yqGdvfL9uBoG8itvNZpXfrrg2ooFTcw9466BmkGrEHJGqoTvxa2EKJDMM4OJWla6xoq3QFJ/BXChPqMmGsY2jMtNgz7umI85Ch/XOtDYgMPJ/1b7NIan1PWanYp+CsKtysX42N98/vtgyfcXkOnQXVgMGkex74jH0iL6bnmGCgqy593IjrbNh7Ll4ntFy391OCeBD6UN/mwHQ1hxQC4edsu5+SJffeLIffnwJBWWMukf4X3emlFYDsdVWhUHXQMD/EyOkjg2kNXkmX3kf90bSMboePqqVHLSyrMDPFyXaNXBnYPmrUmlIscn/YuYctIwKrBEXaORTHCv6joyeHCoKyfz3JzHyo/tXzD/MLyniSQG6viqDB/OrpKqRQw5qBkd6evUlOMk0a8aoQ0jmvbkHDUo gnm7lQ4j hqkI4X7+fVX0ngUOtA3v6vCVdr4nvovU6U2UcCbYc4KcGjdWJ0y4FYsCtY8JyzgXGBbnO2Ha4fdurprGwp9wrl9iJxw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.048986, 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 Tue, Feb 27, 2024 at 4:33=E2=80=AFPM David Hildenbrand wrote: > > On 27.02.24 09:23, Lance Yang wrote: > > Hey David, > > > > Thanks for taking time to review! > > > > On Tue, Feb 27, 2024 at 3:30=E2=80=AFPM David Hildenbrand wrote: > >> > >> On 27.02.24 08:04, Lance Yang wrote: > >>> Previously, in folio_pte_batch(), only the upper boundary of the > >>> folio was checked using '>=3D' for comparison. This led to > >>> incorrect behavior when the next PFN exceeded the lower boundary > >>> of the folio, especially in corner cases where the next PFN might > >>> fall into a different folio. > >> > >> Which commit does this fix? > >> > >> The introducing commit (f8d937761d65c87e9987b88ea7beb7bddc333a0e) is > >> already in mm-stable, so we would need a Fixes: tag. Unless, Ryan's > >> changes introduced a problem. > >> > >> BUT > >> > >> I don't see what is broken. :) > >> > >> Can you please give an example/reproducer? > > > > For example1: > > > > PTE0 is present for large folio1. > > PTE1 is present for large folio1. > > PTE2 is present for large folio1. > > PTE3 is present for large folio1. > > > > folio_nr_pages(folio1) is 4. > > folio_nr_pages(folio2) is 4. > > > > pte =3D *start_ptep =3D PTE0; > > max_nr =3D folio_nr_pages(folio2); > > > > If folio_pfn(folio1) < folio_pfn(folio2), > > the return value of folio_pte_batch(folio2, start_ptep, pte, max_nr) > > will be 4(Actually it should be 0). > > > > For example2: > > > > PTE0 is present for large folio2. > > PTE1 is present for large folio1. > > PTE2 is present for large folio1. > > PTE3 is present for large folio1. > > > > folio_nr_pages(folio1) is 4. > > folio_nr_pages(folio2) is 4. > > > > pte =3D *start_ptep =3D PTE0; > > max_nr =3D folio_nr_pages(folio1); > > > > In both cases, start_ptep does not map the folio. > > It's a BUG in your caller unless I am missing something important. Sorry, I understood. Thanks for your clarification! Lance > > > > If max_nr=3D4, the return value of folio_pte_batch(folio1, start_ptep, > > pte, max_nr) > > will be 1(Actually it should be 0). > > > > folio_pte_batch() will soon be exported, and IMO, these corner cases ma= y need > > to be handled. > > No, you should fix your caller. > > The function cannot possibly do something reasonable if start_ptep does > not map the folio. > > nr =3D pte_batch_hint(start_ptep, pte); > ... > ptep =3D start_ptep + nr; /* nr is >=3D 1 */ > ... > return min(ptep - start_ptep, max_nr); /* will return something > 0 */ > > Which would return > 0 for something that does not map that folio. > > > I was trying to avoid official kernel docs for this internal helper, > maybe we have to improve it now. > > -- > Cheers, > > David / dhildenb >