Skip to content
Commit 4e81a6cb authored by Michael Kelley's avatar Michael Kelley Committed by Martin K. Petersen
Browse files

scsi: storvsc: Don't pass unused PFNs to Hyper-V host



In a SCSI request, storvsc pre-allocates space for up to
MAX_PAGE_BUFFER_COUNT physical frame numbers to be passed to Hyper-V.  If
the size of the I/O request requires more PFNs, a separate memory area of
exactly the correct size is dynamically allocated.

But when the pre-allocated area is used, current code always passes
MAX_PAGE_BUFFER_COUNT PFNs to Hyper-V, even if fewer are needed.  While
this doesn't break anything because the additional PFNs are always zero,
more bytes than necessary are copied into the VMBus channel ring buffer.
This takes CPU cycles and wastes space in the ring buffer. For a typical 4
Kbyte I/O that requires only a single PFN, 248 unnecessary bytes are
copied.

Fix this by setting the payload_sz based on the actual number of PFNs
required, not the size of the pre-allocated space.

Reported-by: default avatarJohn Starks <jostarks@microsoft.com>
Fixes: 8f437105 ("scsi: storvsc: Support PAGE_SIZE larger than 4K")
Signed-off-by: default avatarMichael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1684171241-16209-1-git-send-email-mikelley@microsoft.com


Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent 72a81bb0
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment