Re: [RFC PATCH 12/12] HV/Storvsc: Add bounce buffer support for Storvsc

[Tianyu Lan]

Hi Christoph:
     Thanks a lot for your review. There are some reasons.
     1) Vmbus drivers don't use DMA API now.
     2) Hyper-V Vmbus channel ring buffer already play bounce buffer 
role for most vmbus drivers. Just two kinds of packets from 
netvsc/storvsc are uncovered.
     3) In AMD SEV-SNP based Hyper-V guest, the access physical address 
of shared memory should be bounce buffer memory physical address plus
with a shared memory boundary(e.g, 48bit) reported Hyper-V CPUID. It's
called virtual top of memory(vTom) in AMD spec and works as a watermark. 
So it needs to ioremap/memremap the associated physical address above 
the share memory boundary before accessing them. swiotlb_bounce() uses
low end physical address to access bounce buffer and this doesn't work 
in this senario. If something wrong, please help me correct me.

Thanks.


On 3/1/2021 2:54 PM, Christoph Hellwig wrote:
> This should be handled by the DMA mapping layer, just like for native
> SEV support.