Re: [Xen-devel] [PATCH v3 3/3] xen: introduce XENMEM_get_dma_buf and XENMEM_put_dma_buf

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 08/08/2013 15:16, "Stefano Stabellini" <stefano.stabellini@xxxxxxxxxxxxx>
wrote:

>> This confused me too, this talk of contiguity and being below 4GB. Doesn't
>> this new hypercall behave *exactly* like XENMEM_exchange, except for the
>> additional pinning of the MFNs? If so, just say that in the patch header and
>> code comments. The fact *you* currently use it to get memory below 4GB is an
>> application detail.
> 
> Yeah, you have a good point there. Trying to make the comment clearer I
> actually confused it. I'll fix it.
> 
> 
>> I wonder whether XENMEM_exchange is much use at all in the presence of
>> paging, without the additional semantics of pinning? Perhaps XENMEM_exchange
>> could be suitably adjusted to have the pinning semantics in this case?
> 
> It's not just about pinning, we also need to get the mfn back even if
> the guest is autotranslate, that XENMEM_exchange doesn't do.

Ok, fine by me.

 -- Keir



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