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Date: Fri, 12 Dec 2008 13:18:43 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH 2 of 5] add can_dma/post_dma for direct IO
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To: Blue Swirl <blauwirbel@gmail.com>
Cc: chrisw@redhat.com, Gerd Hoffmann <kraxel@redhat.com>, qemu-devel@nongnu.org, kvm@vger.kernel.org, avi@redhat.com

Blue Swirl wrote:
> On 12/12/08, Andrea Arcangeli <aarcange@redhat.com> wrote:
>   
>> From: Andrea Arcangeli <aarcange@redhat.com>
>>
>>  Add can_dma and post_dma methods needed before/after direct IO to guest
>>  physical memory.
>>
>>  Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
>>     
>
>   
>>  +        /* nonlinear range */
>>  +        if (pd_first != pd)
>>  +            return NULL;
>>     
>
> In my tests on Sparc32, IOMMU can map a linear DVMA range to several
> non-linear physical pages, so this case should be handled correctly.
>   

I think we should go back to Fabrice's earliest suggestion here.  We 
should just have a simple map/unmap lock/unlock API for physical 
memory.  That should be the base API IMHO.

As long the map function goes from guest physical => host virtual, it 
can work for everything we care about.

This is orthogonal to an API dealing with scatter/gather lists and 
translation to and from them.

Regards,

Anthony Liguori