# Re: \[PATCH V3 13/13\] HV/Storvsc: Add Isolation VM support for storvsc driver

- From: Tianyu Lan \<hidden\>
- Date: 2021-08-20 15:38:20 
- List: linux-hyperv
- Page: https://ratatoskr.run/linux-hyperv/2021/08/1484123
- Thread: https://ratatoskr.run/xen-devel/2021/08/1472230/t.md

```text
On 8/20/2021 11:20 PM, Tianyu Lan wrote:
>> The whole approach here is to do dma remapping on each individual page
>> of the I/O buffer.  But wouldn't it be possible to use dma_map_sg() to map
>> each scatterlist entry as a unit?  Each scatterlist entry describes a range of
>> physically contiguous memory.  After dma_map_sg(), the resulting dma
>> address must also refer to a physically contiguous range in the swiotlb
>> bounce buffer memory.   So at the top of the "for" loop over the scatterlist
>> entries, do dma_map_sg() if we're in an isolated VM.  Then compute the
>> hvpfn value based on the dma address instead of sg_page().  But everything
>> else is the same, and the inner loop for populating the pfn_arry is unmodified.
>> Furthermore, the dma_range array that you've added is not needed, since
>> scatterlist entries already have a dma_address field for saving the mapped
>> address, and dma_unmap_sg() uses that field.
>
> I don't use dma_map_sg() here in order to avoid introducing one more loop(e,g dma_map_sg()). We already have a loop to populate cmd_request->dma_range[] and so do the dma map in the same loop.

Sorry for a typo. s/cmd_request->dma_range[]/payload->range.pfn_array[]/
```