Re: [Xen-devel] Re: ATI radeon fails with "iommu=soft swiotlb=force" (seen on RV730/RV740 and RS780/RS800)

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 10/05/09 07:37, Konrad Rzeszutek Wilk wrote:
> Jeremy suggested another one. That is for the Xen IOMMU to fix the virtual
> mappings. Meaning we would swipe out the virtual address of the page to point
> to a virtual address (along with returning an 32-bit bus address) under the 
> 4GB mark.
> That involves also changing the mappings of the old virtual address to the 
> new one
> where ever it may be.
>
> Jeremy, did I get that right?
>   

Yeah.  We'd make xen_dma_map_page() use xen_exchange_memory to replace
the underlying page with something matching the device's requirements. 
That would be fairly straightforward for kernel and vmapped pages, but
it gets pretty complex if the page is mapped into userspace (partly
because of the need to use rmap to find all the user mappings, and
partly because I don't know what the locking/atomicity requirements
would be).

    J


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