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Tue, 27 Feb 2024 10:07:27 -0800 (PST) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id fa42-20020a056a002d2a00b006e55b674e66sm10411pfb.171.2024.02.27.10.07.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 27 Feb 2024 10:07:27 -0800 (PST) Date: Tue, 27 Feb 2024 10:07:26 -0800 From: Kees Cook To: Christophe Leroy Cc: Rick Edgecombe , "Liam.Howlett@oracle.com" , "akpm@linux-foundation.org" , "debug@rivosinc.com" , "broonie@kernel.org" , "kirill.shutemov@linux.intel.com" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "luto@kernel.org" , "peterz@infradead.org" , "hpa@zytor.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "linux-alpha@vger.kernel.org" , "linux-snps-arc@lists.infradead.org" , "linux-arm-kernel@lists.infradead.org" , "linux-csky@vger.kernel.org" , "loongarch@lists.linux.dev" , "linux-mips@vger.kernel.org" , "linux-parisc@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-s390@vger.kernel.org" , "linux-sh@vger.kernel.org" , "sparclinux@vger.kernel.org" Subject: Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info Message-ID: <202402271004.7145FDB53F@keescook> References: <20240226190951.3240433-1-rick.p.edgecombe@intel.com> <20240226190951.3240433-6-rick.p.edgecombe@intel.com> <94a2b919-e03b-4ade-b13e-7774849dc02b@csgroup.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <94a2b919-e03b-4ade-b13e-7774849dc02b@csgroup.eu> X-Rspamd-Queue-Id: D6CFE14000D X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: xjgs5o1bddgg6gjfkaz6h9spqetj1hc1 X-HE-Tag: 1709057248-785553 X-HE-Meta: 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 nV5tJM2K Mh4K7cbuQo6Yj9x1GEWQrzSvF3fBO0mmoALmIFfNRFiuABZnlRqtSR/3X5qUkhfIYCSxTiAIRNQrVq9sNRSQ4/mS/VHdke9G2BWatjKys1q/CUpoi/KEThofQGxDr97jBdN6caPj4yQtO8vvpDOAlruNyniS88lr61tmf2LkX89aoJGc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, 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 07:02:59AM +0000, Christophe Leroy wrote: > > > Le 26/02/2024 à 20:09, Rick Edgecombe a écrit : > > Future changes will need to add a field to struct vm_unmapped_area_info. > > This would cause trouble for any archs that don't initialize the > > struct. Currently every user sets each field, so if new fields are > > added, the core code parsing the struct will see garbage in the new > > field. > > > > It could be possible to initialize the new field for each arch to 0, but > > instead simply inialize the field with a C99 struct inializing syntax. > > Why doing a full init of the struct when all fields are re-written a few > lines after ? It's a nice change for robustness and makes future changes easier. It's not actually wasteful since the compiler will throw away all redundant stores. > If I take the exemple of powerpc function slice_find_area_bottomup(): > > struct vm_unmapped_area_info info; > > info.flags = 0; > info.length = len; > info.align_mask = PAGE_MASK & ((1ul << pshift) - 1); > info.align_offset = 0; But one cleanup that is possible from explicitly zero-initializing the whole structure would be dropping all the individual "= 0" assignments. :) -- Kees Cook