From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH 3/3] domctl: pause vCPU for context reads Date: Wed, 5 Feb 2014 15:43:34 +0000 Message-ID: <52F25C26.10606@citrix.com> References: <52F25D4202000078001196AB@nat28.tlf.novell.com> <52F25EB702000078001196EC@nat28.tlf.novell.com> <52F258CF.50706@citrix.com> <52F2695002000078001197AB@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1WB4dW-0002h0-Hv for xen-devel@lists.xenproject.org; Wed, 05 Feb 2014 15:43:38 +0000 In-Reply-To: <52F2695002000078001197AB@nat28.tlf.novell.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: Jan Beulich Cc: George Dunlap , xen-devel , Keir Fraser List-Id: xen-devel@lists.xenproject.org On 05/02/14 15:39, Jan Beulich wrote: >>>> On 05.02.14 at 16:29, Andrew Cooper wrote: >> On 05/02/14 14:54, Jan Beulich wrote: >>> "Base" context reads already paused the subject vCPU when being the >>> current one, but that special case isn't being properly dealt with >>> anyway (at the very least when x86's fsgsbase feature is in use), so >>> just disallow it. >>> >>> "Extended" context reads so far didn't do any pausing. >>> >>> While we can't avoid the reported data being stale by the time it >>> arrives at the caller, this way we at least guarantee that it is >>> consistent. >>> >>> Signed-off-by: Jan Beulich >> Now I come to think about it, is this an ABI change, as we are now >> disallowing a control domain to issue these hypercalls on itself? > Of course it is, and intentionally so. As was patch 2. And imo it > was never correct to allow this. > > Jan > It is certainly possible to get libxc to do this, but I would agree that it has no valid use. Reviewed-by: Andrew Cooper