Messages in this thread | | | Date | Tue, 28 Jun 2022 16:50:09 -0700 | Subject | Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS | From | Bart Van Assche <> |
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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 >> <schmitzmic@gmail.com> 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.
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