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[70.52.229.124]) by smtp.gmail.com with ESMTPSA id x16-20020ae9e910000000b00746aa080eefsm205950qkf.6.2023.03.30.15.22.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Mar 2023 15:22:09 -0700 (PDT) Date: Thu, 30 Mar 2023 18:22:08 -0400 From: Peter Xu To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Kravetz , Andrew Morton , Andrea Arcangeli , Mike Rapoport , Axel Rasmussen , Nadav Amit , Leonardo Bras Soares Passos , linux-stable Subject: Re: [PATCH 01/29] Revert "userfaultfd: don't fail on unrecognized features" Message-ID: References: <20230330155707.3106228-1-peterx@redhat.com> <20230330155707.3106228-2-peterx@redhat.com> <6eb02bdd-e69e-d277-c44c-0aefb23430bb@redhat.com> MIME-Version: 1.0 In-Reply-To: <6eb02bdd-e69e-d277-c44c-0aefb23430bb@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Queue-Id: 1ADC2100006 X-Rspamd-Server: rspam01 X-Stat-Signature: oqfeucutbs5xr9nn55pzf1ytodkhi7hw X-HE-Tag: 1680214932-932893 X-HE-Meta: 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 gEGO58hK 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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: On Thu, Mar 30, 2023 at 08:31:30PM +0200, David Hildenbrand wrote: > On 30.03.23 17:56, Peter Xu wrote: > > This is a proposal to revert commit 914eedcb9ba0ff53c33808. > > > > I found this when writting a simple UFFDIO_API test to be the first unit > > test in this set. Two things breaks with the commit: > > > > - UFFDIO_API check was lost and missing. According to man page, the > > kernel should reject ioctl(UFFDIO_API) if uffdio_api.api != 0xaa. This > > check is needed if the api version will be extended in the future, or > > user app won't be able to identify which is a new kernel. > > Agreed. > > > > > - Feature flags checks were removed, which means UFFDIO_API with a > > feature that does not exist will also succeed. According to the man > > page, we should (and it makes sense) to reject ioctl(UFFDIO_API) if > > unknown features passed in. > > > > Agreed. > > I understand the motivation of the original commit, but it should not have > changed existing checks/functionality. Introducing a different way to enable > such functionality on explicit request would be better. But maybe simple > feature probing (is X support? is Y supported? is Z supported) might be > easier without requiring ABI changes. Yes, I mentioned a similar "proposal" of UFFDIO_FEATURES here too, simply returning the feature bitmask before UFFDIO_API: https://lore.kernel.org/all/ZCSUTSbAcwBINiNk@x1n/ But I think current way is still fine; so maybe we'd just not bother. > > I assume we better add > > Fixes: 914eedcb9ba0 ("userfaultfd: don't fail on unrecognized features") Yes I'll add it. > Acked-by: David Hildenbrand Thanks, -- Peter Xu