From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH 12/17] xenpaging: handle HVMCOPY_gfn_paged_out in copy_from/to_user Date: Wed, 15 Dec 2010 11:35:21 +0000 Message-ID: References: <20101206205912.343173055@aepfle.de> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20101206205912.343173055@aepfle.de> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Olaf Hering , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 06/12/2010 20:59, "Olaf Hering" wrote: > mem_event_put_request(d, &req); > + > + if ( req.flags & MEM_EVENT_FLAG_VCPU_PAUSED ) > + { > + wait_event(d->wq, mfn_valid(gfn_to_mfn(p2m, gfn, &p2mt)) && > !p2m_is_paging(p2mt)); > + } > + This I find interesting. Do you not race the xenpaging daemon satisfying your page-in request, but then very quickly paging it out again? In which case you might never wake up! I think the condition you wait on should be for a response to your paging request. A wake_up() alone is not really sufficient; you need some kind of explicit flagging to the vcpu too. Could the paging daemon stick a response in a shared ring, or otherwise explicitly flag to this vcpu that it's request has been fully satisfied and it's time to wake up and retry its operation? Well, really that's a rhetorical question, because that is exactly what you need to implement for this waitqueue strategy to work properly! -- Keir