scsi: storvsc: Correct reporting of Hyper-V I/O size limits

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Current code is based on the idea that the max number of SGL entries
also determines the max size of an I/O request.  While this idea was
true in older versions of the storvsc driver when SGL entry length
was limited to 4 Kbytes, commit 3d9c3dcc58 ("scsi: storvsc: Enable
scatterlist entry lengths > 4Kbytes") removed that limitation. It's
now theoretically possible for the block layer to send requests that
exceed the maximum size supported by Hyper-V. This problem doesn't
currently happen in practice because the block layer defaults to a
512 Kbyte maximum, while Hyper-V in Azure supports 2 Mbyte I/O sizes.
But some future configuration of Hyper-V could have a smaller max I/O
size, and the block layer could exceed that max.

Fix this by correctly setting max_sectors as well as sg_tablesize to
reflect the maximum I/O size that Hyper-V reports. While allowing
I/O sizes larger than the block layer default of 512 Kbytes doesn’t
provide any noticeable performance benefit in the tests we ran, it's
still appropriate to report the correct underlying Hyper-V capabilities
to the Linux block layer.

Also tweak the virt_boundary_mask to reflect that the required
alignment derives from Hyper-V communication using a 4 Kbyte page size,
and not on the guest page size, which might be bigger (eg. ARM64).

Link: https://lore.kernel.org/r/1655190355-28722-1-git-send-email-ssengar@linux.microsoft.com
Fixes: 3d9c3dcc58 ("scsi: storvsc: Enable scatter list entry lengths > 4Kbytes")
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

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Saurabh Sengar 2022-06-14 00:05:55 -07:00 • committed by Martin K. Petersen

parent 2acd76e7b8

commit 1d3e098078

1 changed files with 22 additions and 5 deletions

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drivers/scsi/storvsc_drv.c

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