From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH v6 24/29] xen/x86: allow HVM guests to use hypercalls to bring up vCPUs Date: Tue, 29 Sep 2015 11:00:04 +0100 Message-ID: <560A6124.2090404@citrix.com> References: <1441368548-43465-1-git-send-email-roger.pau@citrix.com> <1441368548-43465-25-git-send-email-roger.pau@citrix.com> <5600420C02000078000A4234@prv-mh.provo.novell.com> <5609664D.8060604@citrix.com> <560A555402000078000A6625@prv-mh.provo.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1Zgri4-000521-LV for xen-devel@lists.xenproject.org; Tue, 29 Sep 2015 10:00:32 +0000 In-Reply-To: <560A555402000078000A6625@prv-mh.provo.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 , =?UTF-8?B?Um9nZXIgUGF1IE1vbm7DqQ==?= Cc: George Dunlap , xen-devel@lists.xenproject.org, Stefano Stabellini , Ian Campbell , Tim Deegan List-Id: xen-devel@lists.xenproject.org On 29/09/15 08:09, Jan Beulich wrote: > >>>> + uint32_t cs_base; >>>> + uint32_t ds_base; >>>> + uint32_t ss_base; >>> I continue to question why we have DS here, but not ES (and maybe >>> FS and GS too). I.e. either just CS and SS (which are architecturally >>> required) or at least all four traditional x86 segment registers. And >>> you're also clearly not targeting minimal state, or else there likely >>> wouldn't be a need for e.g. R8-R15 in the 64-bit variant. >> I'm fine with removing r8-15. Regarding the segment selectors, I don't >> have a problem with only allowing CS and SS to be set, or all of them >> including FS and GS. But I would like to get a consensus on this, we >> have already gone back and forth several times regarding how this >> structure should look like, and TBH, I was hoping that this was the last >> time. > Was there back and forth? I only recall always having asked for > consistency here, just like spelled out above. > >> Andrew, Jan, what would you prefer, either DS is removed or ES, FS and >> GS are also added? > I voiced my opinion. Andrew? DS clearly needs initialising to provide a sane environment in the newly running vcpu. Expecting %cs or %ss overrides until a new GDT is loaded is unreasonable IMO. Therefore, we are back to the question of whether to provide all segment registers, or specify a flat layout without specific selector values. I would prefer the former to the latter. ~Andrew