[PATCH 1/1] scsi: storvsc: Fix swiotlb bounce buffer leak in confidential VM

[Michael Kelley <mikelley@microsoft.com>]

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: 743b237c3a7b ("scsi: storvsc: Add Isolation VM support for storvsc driver")
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
---
 drivers/scsi/storvsc_drv.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 3c5b7e4..55d6fb4 100644
--- 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;
-- 
1.8.3.1