On 12/9/2021 4:00 PM, Long Li wrote:

quoted

@@ -1848,21 +1851,22 @@ static int storvsc_queuecommand(struct Scsi_Host

*host, struct scsi_cmnd *scmnd)
  		payload->range.len = length;
  		payload->range.offset = offset_in_hvpg;

+		sg_count = scsi_dma_map(scmnd);
+		if (sg_count < 0)
+			return SCSI_MLQUEUE_DEVICE_BUSY;

Hi Tianyu,

This patch (and this patch series) unconditionally adds code for dealing with DMA addresses for all VMs, including non-isolation VMs.

Does this add performance penalty for VMs that don't require isolation?

Hi Long:
	scsi_dma_map() in the traditional VM just save sg->offset to
sg->dma_address and no data copy because swiotlb bounce buffer code
doesn't work. The data copy only takes place in the Isolation VM and
swiotlb_force is set. So there is no additional overhead in the 
traditional VM.

Thanks.