Hi Bart,
On 29/06/22 11:50, Bart Van Assche wrote:
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@xxxxxxxxx> 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
Thanks - four byte alignment actually wouldn't be an issue for me. It's
two byte or smaller that would trip up the SCSI DMA.
While I'm sure such an even more pathological test case could be
written, I was rather worried about st.c and sr.c input ...
Cheers,
Michael
Bart.
