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    SubjectRe: [RFC PATCH v4 0/2] RDMA/rxe: Add dma-buf support
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    Am 10.12.21 um 13:42 schrieb Jason Gunthorpe:
    > On Fri, Dec 10, 2021 at 08:29:24PM +0900, Shunsuke Mie wrote:
    >> Hi Jason,
    >> Thank you for replying.
    >>
    >> 2021年12月8日(水) 2:14 Jason Gunthorpe <jgg@ziepe.ca>:
    >>> On Fri, Dec 03, 2021 at 12:51:44PM +0900, Shunsuke Mie wrote:
    >>>> Hi maintainers,
    >>>>
    >>>> Could you please review this patch series?
    >>> Why is it RFC?
    >>>
    >>> I'm confused why this is useful?
    >>>
    >>> This can't do copy from MMIO memory, so it shouldn't be compatible
    >>> with things like Gaudi - does something prevent this?
    >> I think if an export of the dma-buf supports vmap, CPU is able to access the
    >> mmio memory.
    >>
    >> Is it wrong? If this is wrong, there is no advantages this changes..
    > I don't know what the dmabuf folks did, but yes, it is wrong.
    >
    > IOMEM must be touched using only special accessors, some platforms
    > crash if you don't do this. Even x86 will crash if you touch it with
    > something like an XMM optimized memcpy.
    >
    > Christian? If the vmap succeeds what rules must the caller use to
    > access the memory?

    See dma-buf-map.h and especially struct dma_buf_map.

    MMIO memory is perfectly supported here and actually the most common case.

    Christian.

    >
    > Jason

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