Re: [Xen-devel] The mfn of the frame, that holds a mlock-ed PV domU usermode page, can change

[Joanna Rutkowska <joanna@xxxxxxxxxxxxxxxxxxxxxx>]

On 04/12/2010 11:26 PM, Jeremy Fitzhardinge wrote:
> On 04/12/2010 02:19 PM, Joanna Rutkowska wrote:
>> Right, that's for the "ring" page, which we use to implement a ring
>> buffer, and we then pass mfns of the actual Xorg's composition buffers
>> over this ring buffer to Dom0.
>>
>> Interestingly, I have never seen a garbage in any of the composition
>> buffers (which are directly displayed by our appviewers, so it would be
>> immediately visible), just like if only the mfn for the "ring" page
>> could be modified, but the composition buffer's mfn were somehow pinned...
>>
>> This might suggest that the memory used by the composition buffers
>> (which are in usermode) is somehow locked?
>>   
> 
> Worth looking into.
> 
> I'm not at all familiar with how X manages composition buffers, but it
> seems to me that in normal use, one would want to be able to either
> allocate that buffer in texture memory (so it can be used as a texture
> source), or at least copy updates into texture memory.  Couldn't you
> hook into that transfer to the composition hardware (ie, dom0)?
> 

We will definitely look into this. Thanks a lot for your help, Jeremy!

joanna.

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