From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: arch_set_info_guest() and cr1 Date: Thu, 22 Sep 2011 16:31:18 -0700 Message-ID: <4E7BC546.9030607@goop.org> References: <20110811190315.1cc6afab@mantra.us.oracle.com> <20110812150115.6047b8c2@mantra.us.oracle.com> <4E45DED5.40602@goop.org> <1316676757.23371.2.camel@zakaz.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1316676757.23371.2.camel@zakaz.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Ian Campbell Cc: "Xen-devel@lists.xensource.com" , Tim Deegan , Keir Fraser List-Id: xen-devel@lists.xenproject.org On 09/22/2011 12:32 AM, Ian Campbell wrote: > (old mail, I know) > > On Sat, 2011-08-13 at 03:17 +0100, Jeremy Fitzhardinge wrote: >> On 08/12/2011 03:01 PM, Mukesh Rathor wrote: >>> Ah I see it, during save/restore, it is used. >>> Well, I'm trying to keep the option of using PV paging with hybrid, so >>> I may need to honor that. But that's phase 2. >> Though it would be nice to re-enable the use of PV writable pagetables >> to get access to HAP, and we could do without that. >> >> Does Xen require that the user pagetable be a proper subset of the >> kernel pagetable? If we can assume that and get proper ring protections >> in the HVM container, then we can simply ignore the user pagetable (and >> would have to if we want to get good syscall performance). > IIRC back when I did the (now completely defunct) supervisor mode kernel > stuff that was exactly the assumption which was made and it certainly > worked in practice (although "require" might be a strong term). Well, I guess we could add ELF notes to allow a guest to say "I really need separate non-intersecting user/kernel pagetables" if they really need it. Or repurpose auto_translated_physmap to also mean "no separate user/kernel pagetables required". Has that ever been supported for 64-bit PV guests? My memory of the chronology is that it died as a feature at about the time that 64-bit support went in. J