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[86.156.84.164]) by smtp.gmail.com with ESMTPSA id x10-20020a5d54ca000000b0030903371ef9sm3529304wrv.22.2023.05.17.12.03.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 May 2023 12:03:46 -0700 (PDT) Date: Wed, 17 May 2023 20:03:45 +0100 From: Lorenzo Stoakes To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , "Liam R . Howlett" , Mark Rutland , Andrea Arcangeli , Mike Rapoport , Alexander Viro , linux-stable Subject: Re: [PATCH 1/2] mm/uffd: Fix vma operation where start addr cuts part of vma Message-ID: References: <20230517150408.3411044-1-peterx@redhat.com> <20230517150408.3411044-2-peterx@redhat.com> <4a68aee6-68d9-4d17-bb7f-cda3910f6f1f@lucifer.local> <99566f92-9b97-4b2b-b75b-860532e851fd@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: ufjxxffkx4bnp7ruzi1q35ayf335pkaa X-Rspam-User: X-Rspamd-Queue-Id: 721581A0022 X-Rspamd-Server: rspam07 X-HE-Tag: 1684350229-961638 X-HE-Meta: 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 F8wDkMpd aeujWdIBD6zXHhYmovMNzpqePk968pCxSQaJGrVXt45YffMDfTsGX4bVoM026ao9NUiiJ+znyGJ8E/NE33ClRtkrN7o+ceoBbmY+GOt5oB8YUA/8Wy0QtTMHjSLNz3XV7Kzv1/skMAWHOPrdWkfHTknadOjwlhgK0bxAxZeDFXwVefs7uod/kLotl5LPKHzfp4xAJHJEvQi6WugrX0xbxaAYtcZWPIQQahXD36IjphRMgJzkOBffe6aHu//81gFunbroA15G7bYpGgzQ0d29kDrVTlV32oo/D6PEMaFBCiRpVrMLhcSo0hme5ho/wyAYJZw/2BIkMn7jTA0C+7QEheFpdDvieSJhELIXv0Jzwt78JKSX7KfJ0FEwNc+bxsC8YkpSsGOLqPPheQLiqkAzNiexE87Ku+uvdAV1SFrcMcwMg8+TX6BYV/TNXD2RDRrs1pomeMk8sR87HvY273KjyE+UQUHGYwNl75J7R 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: On Wed, May 17, 2023 at 02:54:39PM -0400, Peter Xu wrote: > On Wed, May 17, 2023 at 07:40:59PM +0100, Lorenzo Stoakes wrote: > > On Wed, May 17, 2023 at 02:37:41PM -0400, Peter Xu wrote: > > > On Wed, May 17, 2023 at 06:20:55PM +0100, Lorenzo Stoakes wrote: > > > > On Wed, May 17, 2023 at 11:04:07AM -0400, Peter Xu wrote: > > > > > It seems vma merging with uffd paths is broken with either > > > > > register/unregister, where right now we can feed wrong parameters to > > > > > vma_merge() and it's found by recent patch which moved asserts upwards in > > > > > vma_merge() by Lorenzo Stoakes: > > > > > > > > > > https://lore.kernel.org/all/ZFunF7DmMdK05MoF@FVFF77S0Q05N.cambridge.arm.com/ > > > > > > > > > > The problem is in the current code base we didn't fixup "prev" for the case > > > > > where "start" address can be within the "prev" vma section. In that case > > > > > we should have "prev" points to the current vma rather than the previous > > > > > one when feeding to vma_merge(). > > > > > > > > This doesn't seem quite correct, perhaps - "where start is contained within vma > > > > but not clamped to its start. We need to convert this into case 4 which permits > > > > subdivision of prev by assigning vma to prev. As we loop, each subsequent VMA > > > > will be clamped to the start." > > > > > > I think it covers more than case 4 - it can also be case 0 where no merge > > > will happen? > > > > Ugh please let's not call a case that doesn't merge by a number :P but sure of > > course it might also not merge. > > To me the original paragraph was still fine. But if you prefer your version > (which I'm perfectly fine either way if you'd like to spell out what cases > it'll trigger), it'll be: > > It's possible that "start" is contained within vma but not clamped to its > start. We need to convert this into either "cannot merge" case or "can > merge" case 4 which permits subdivision of prev by assigning vma to > prev. As we loop, each subsequent VMA will be clamped to the start. > > Does that look good to you? > Looks good to me, thanks for taking the time! > Thanks, > > -- > Peter Xu >