From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH v3 3/3] xen: introduce XENMEM_get_dma_buf and XENMEM_put_dma_buf Date: Thu, 08 Aug 2013 15:47:05 +0100 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Stefano Stabellini Cc: xen-devel@lists.xensource.com, tim@xen.org, Ian Campbell List-Id: xen-devel@lists.xenproject.org On 08/08/2013 15:16, "Stefano Stabellini" 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