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Re: [Xen-devel] [PATCH RFC 0/3] introduce XENMEM_get_dma_buf and XENMEM_put_dma_buf

On 31/07/13 18:57, Stefano Stabellini wrote:
> Hi all,
> this patch series introduces two new hypercalls to allow autotranslate
> guests to allocate a contiguous buffer in machine addresses.
> The XENMEM_get_dma_buf returns the mfns and makes sure to pin the pages
> so that the hypervisor won't change their p2m mappings while in use.
> XENMEM_put_dma_buf simply unpins the pages.

Can you expand on what circumstances the hypervisor would otherwise
adjust the p2m?  How has x86 avoided these problems?

> The implementation of XENMEM_put_dma_buf is missing, as it's actually
> unused.
> The page pinning is also missing from this series. I would appreciate
> feedback on the best way to implement it, especially on x86.


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