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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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