On 8/20/2021 11:20 PM, Tianyu Lan wrote:

quoted

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[]/