Re: [RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address setting function

[Robin Murphy]

On 2021-06-07 07:43, Christoph Hellwig wrote:
> On Sun, May 30, 2021 at 11:06:25AM -0400, Tianyu Lan wrote:
> > From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>
> >
> > For Hyper-V isolation VM with AMD SEV SNP, the bounce buffer(shared memory)
> > needs to be accessed via extra address space(e.g address above bit39).
> > Hyper-V code may remap extra address space outside of swiotlb. swiotlb_
> > bounce() needs to use remap virtual address to copy data from/to bounce
> > buffer. Add new interface swiotlb_set_bounce_remap() to do that.
>
> Why can't you use the bus_dma_region ranges to remap to your preferred
> address?

FWIW, I think a better generalisation for this would be allowing 
set_memory_decrypted() to return an address rather than implicitly 
operating in-place, and hide all the various hypervisor hooks behind that.

Robin.