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

[Tianyu Lan <ltykernel@xxxxxxxxx>]

On 6/7/2021 10:56 PM, Tianyu Lan wrote:
> On 6/7/2021 2:43 PM, 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?
> Thanks for your suggestion.
>
> These addresses in extra address space works as system memory mirror. 
> The shared memory with host in Isolation VM needs to be accessed via 
> extra address space which is above shared gpa boundary. During 
> initializing swiotlb bounce buffer pool, only address bellow shared gpa 
> boundary can be accepted by swiotlb API because it is treated as system 
> memory and managed by memory management. This is why Hyper-V swiotlb 
> bounce buffer pool needs to be allocated in Hyper-V code and map
> associated physical address in extra address space. The patch target is
> to add the new interface to set start virtual address of bounce buffer
> pool and let swiotlb boucne buffer copy function to use right virtual 
> address for extra address space.
> bus_dma_region is to translate cpu physical address to dma address.
> It can't modify the virtual address of bounce buffer pool and let
> swiotlb code to copy data with right address. If some thing missed,
> please correct me.
Hi Christoph:
        Sorry to bother you. Could you have a look at my previous reply?
I try figuring out the right way.

Thanks.