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SubjectRe: [RFC PATCH V3 08/11] swiotlb: Add bounce buffer remap address setting function
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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@microsoft.com>
>>>
>>> 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.

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