This is a note to let you know that I've just added the patch titled
scsi: storvsc: Don't pass unused PFNs to Hyper-V host
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
scsi-storvsc-don-t-pass-unused-pfns-to-hyper-v-host.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 66c17b18edb7213498699afd13a896105aff35c3
Author: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Date: Mon May 15 10:20:41 2023 -0700
scsi: storvsc: Don't pass unused PFNs to Hyper-V host
[ Upstream commit 4e81a6cba517cb33584308a331f14f5e3fec369b ]
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: John Starks <jostarks@xxxxxxxxxxxxx>
Fixes: 8f43710543ef ("scsi: storvsc: Support PAGE_SIZE larger than 4K")
Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1684171241-16209-1-git-send-email-mikelley@xxxxxxxxxxxxx
Signed-off-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index a0665bca54b99..5284f9a0b826e 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1780,7 +1780,7 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
length = scsi_bufflen(scmnd);
payload = (struct vmbus_packet_mpb_array *)&cmd_request->mpb;
- payload_sz = sizeof(cmd_request->mpb);
+ payload_sz = 0;
if (scsi_sg_count(scmnd)) {
unsigned long offset_in_hvpg = offset_in_hvpage(sgl->offset);
@@ -1789,10 +1789,10 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
unsigned long hvpfn, hvpfns_to_add;
int j, i = 0, sg_count;
- if (hvpg_count > MAX_PAGE_BUFFER_COUNT) {
+ payload_sz = (hvpg_count * sizeof(u64) +
+ sizeof(struct vmbus_packet_mpb_array));
- payload_sz = (hvpg_count * sizeof(u64) +
- sizeof(struct vmbus_packet_mpb_array));
+ if (hvpg_count > MAX_PAGE_BUFFER_COUNT) {
payload = kzalloc(payload_sz, GFP_ATOMIC);
if (!payload)
return SCSI_MLQUEUE_DEVICE_BUSY;
