From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Scalable Event Channel ABI design (draft A) Date: Wed, 06 Feb 2013 10:41:04 +0000 Message-ID: References: <1360143520.23001.55.camel@zakaz.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1360143520.23001.55.camel@zakaz.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: Wei Liu , David Vrabel , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 06/02/2013 09:38, "Ian Campbell" wrote: >>> VCPUOP_register_vcpu_info doesn't require each vcpu_info to be on a page >>> by itself, even if that happens to be the Linux implementation today (I >>> haven't checked that). >> >> Having guest agree that vcpu_info grows by size of the per-vcpu control >> block, if using this new event-channel interface, is reasonable though. > > Can only use this trick once though, so it might be blocking ourselves > into a future ABI corner. > > Is there a downside to registering the control block separately? The > guest can always arrange for them to be contiguous if it wants, or if we > are worried about the number of global mappings then the hypervisor > could require it shares a page with the vcpu_info but allow the offset > to be specified separately. I would say we consider vcpu_info to be versioned, and that using the new event-channel interface requires use of at least v2 of the vcpu_info structure. There is a rsvd field in register_vcpu_info hypercall that could be used for specifying such a thing, although sadly it is not currently checked to be zero, so we may not actually be able to make use of those bits. -- Keir