scsi: storvsc: Fix swiotlb bounce buffer leak in confidential VM

[ Upstream commit 67ff3d0a49f3d445c3922e30a54e03c161da561e ]

storvsc_queuecommand() maps the scatter/gather list using scsi_dma_map(),
which in a confidential VM allocates swiotlb bounce buffers. If the I/O
submission fails in storvsc_do_io(), the I/O is typically retried by higher
level code, but the bounce buffer memory is never freed.  The mostly like
cause of I/O submission failure is a full VMBus channel ring buffer, which
is not uncommon under high I/O loads.  Eventually enough bounce buffer
memory leaks that the confidential VM can't do any I/O. The same problem
can arise in a non-confidential VM with kernel boot parameter
swiotlb=force.

Fix this by doing scsi_dma_unmap() in the case of an I/O submission
error, which frees the bounce buffer memory.

Fixes: 3fbc09f2d5ba ("scsi: storvsc: Add Isolation VM support for storvsc driver")
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1670183564-76254-1-git-send-email-mikelley@microsoft.com
Tested-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 3c5b7e4227b25e3d44795d26ad70974a32add542..55d6fb4526804dd670ec40e234509d65cc89dc58 100644 (file)
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1823,6 +1823,9 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
        ret = storvsc_do_io(dev, cmd_request, get_cpu());
        put_cpu();
 
+       if (ret)
+               scsi_dma_unmap(scmnd);
+
        if (ret == -EAGAIN) {
                /* no more space */
                ret = SCSI_MLQUEUE_DEVICE_BUSY;