From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [PATCH RFC 0/3] introduce XENMEM_get_dma_buf and
 XENMEM_put_dma_buf
Date: Thu, 1 Aug 2013 10:41:06 +0100
Message-ID: <51FA2D32.4050001@citrix.com>
References: <alpine.DEB.2.02.1307311850010.4893@kaball.uk.xensource.com>
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To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: xen-devel@lists.xensource.com, Tim Deegan <tim@xen.org>, Ian Campbell <Ian.Campbell@citrix.com>
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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.

David