On 8/12/2021 8:27 PM, Christoph Hellwig wrote:

This is still broken.  You need to make sure the actual DMA allocations
do have struct page backing.

Hi Christoph:
      swiotlb_tbl_map_single() still returns PA below vTOM/share_gpa_
boundary. These PAs has backing pages and belong to system memory.
In other word, all PAs passed to DMA API have backing pages and these is 
no difference between Isolation guest and traditional guest for DMA API.
The new mapped VA for PA above vTOM here is just to access the bounce 
buffer in the swiotlb code and isn't exposed to outside.