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([2601:647:4000:d7:feaa:14ff:fe9d:6dbd]) by smtp.gmail.com with ESMTPSA id cr9-20020a056a000f0900b0052594a3ba89sm6923182pfb.65.2022.06.28.16.50.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Jun 2022 16:50:13 -0700 (PDT) Message-ID: Date: Tue, 28 Jun 2022 16:50:09 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS Content-Language: en-US To: Michael Schmitz , Arnd Bergmann References: <20220617125750.728590-1-arnd@kernel.org> <20220617125750.728590-4-arnd@kernel.org> <6ba86afe-bf9f-1aca-7af1-d0d348d75ffc@gmail.com> <9289fd82-285c-035f-5355-4d70ce4f87b0@gmail.com> <9f812d3d-0fcd-46e6-6d7e-6d4bf66f24ab@gmail.com> From: Bart Van Assche In-Reply-To: <9f812d3d-0fcd-46e6-6d7e-6d4bf66f24ab@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Marek Szyprowski , Linux-Arch , scsi , Christoph Hellwig , Geert Uytterhoeven , Jakub Kicinski , Arnd Bergmann , Denis Efremov , linux-m68k , John Paul Adrian Glaubitz , Khalid Aziz , Miquel van Smoorenburg , Parisc List , Robin Murphy , Matt Wang , Linux Kernel Mailing List , Mark Salyzyn , Linux IOMMU , alpha , linuxppc-dev , "Maciej W . Rozycki" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 6/28/22 16:09, Michael Schmitz wrote: > On 29/06/22 09:50, Arnd Bergmann wrote: >> On Tue, Jun 28, 2022 at 11:03 PM Michael Schmitz >> wrote: >>> On 28/06/22 19:03, Geert Uytterhoeven wrote: >>>>> The driver allocates bounce buffers using kmalloc if it hits an >>>>> unaligned data buffer - can such buffers still even happen these days? >>>> No idea. >>> Hmmm - I think I'll stick a WARN_ONCE() in there so we know whether this >>> code path is still being used. >> kmalloc() guarantees alignment to the next power-of-two size or >> KMALLOC_MIN_ALIGN, whichever is bigger. On m68k this means it >> is cacheline aligned. > > And all SCSI buffers are allocated using kmalloc? No way at all for user > space to pass unaligned data? > > (SCSI is a weird beast - I have used a SCSI DAT tape driver many many > years ago, which broke all sorts of assumptions about transfer block > sizes ... but that might actually have been in the v0.99 days, many > rewrites of SCSI midlevel ago). > > Just being cautious, as getting any of this tested will be a stretch. An example of a user space application that passes an SG I/O data buffer to the kernel that is aligned to a four byte boundary but not to an eight byte boundary if the -s (scattered) command line option is used: https://github.com/osandov/blktests/blob/master/src/discontiguous-io.cpp Bart.