From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH 00/10] x86/hvm: pkeys, add memory protection-key support Date: Tue, 17 Nov 2015 16:24:15 +0000 Message-ID: <564B54AF.9030009@citrix.com> References: <1447669917-17939-1-git-send-email-huaitong.han@intel.com> <564A1652.70202@citrix.com> <564B0ED902000078000B5C8E@prv-mh.provo.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <564B0ED902000078000B5C8E@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 Cc: kevin.tian@intel.com, wei.liu2@citrix.com, ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com, george.dunlap@eu.citrix.com, ian.jackson@eu.citrix.com, xen-devel@lists.xen.org, jun.nakajima@intel.com, Huaitong Han , keir@xen.org List-Id: xen-devel@lists.xenproject.org On 17/11/15 10:26, Jan Beulich wrote: >>>> On 16.11.15 at 18:45, wrote: >> Furthermore, it is unclear (given the unwritten ABI) whether it is even >> safe to move _PAGE_GNTTAB out of the way, as this is visible to a PV guest. > It seems pretty clear to me that this would be unsafe: It being > part of L1_DISALLOW_MASK, if it moved and a guest used the > bit for its own purposes, the guest would break. I guess we'll > need an ELF note by which the guest can advertise which of the > available bits it doesn't care about itself. Well - it depends whether any of these bits actually get used. If none actually do get used, we would be better to retro-fit a real ABI in place, without requiring all new guests to opt-in to get new features. ~Andrew