Re: [PATCH 1/1] virtio_ring: fix return code on DMA mapping fails

[Christoph Hellwig]

On Thu, Nov 28, 2019 at 12:42:25AM +0000, Ashish Kalra wrote:
> Why can't we leverage CMA instead of SWIOTLB for DMA when SEV is
> enabled, CMA is well integerated with the DMA subsystem and handles
> encrypted pages when force_dma_unencrypted() returns TRUE. 
> 
> Though, CMA might face the same issues as SWIOTLB bounce buffers, it's
> size is similarly setup statically as SWIOTLB does or can be set as a 
> percentage of the available system memory.

How is CMA integrated with SEV?  CMA just gives a contiguous chunk
of memory, which still needs to be remapped as unencrypted before
returning it to the user.