From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755256AbaFBQwf (ORCPT ); Mon, 2 Jun 2014 12:52:35 -0400 Received: from one.firstfloor.org ([193.170.194.197]:52288 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752278AbaFBQwe (ORCPT ); Mon, 2 Jun 2014 12:52:34 -0400 Date: Mon, 2 Jun 2014 18:52:31 +0200 From: Andi Kleen To: Gleb Natapov Cc: Andi Kleen , Andi Kleen , peterz@infradead.org, pbonzini@redhat.com, eranian@google.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mtosatti@redhat.com Subject: Re: [PATCH 4/4] kvm: Implement PEBS virtualization Message-ID: <20140602165231.GP25366@two.firstfloor.org> References: <1401412327-14810-1-git-send-email-andi@firstfloor.org> <1401412327-14810-5-git-send-email-andi@firstfloor.org> <20140530082136.GA4715@minantech.com> <20140530162424.GC8876@tassilo.jf.intel.com> <20140602164534.GD4715@minantech.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140602164534.GD4715@minantech.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org BTW I found some more problems in the v1 version. > > > With EPT it is less likely to happen (but still possible IIRC depending on memory > > > pressure and how much memory shadow paging code is allowed to use), without EPT > > > it will happen for sure. > > > > Don't care about the non EPT case, this is white listed only for EPT supporting > > CPUs. > User may still disable EPT during module load, so pebs should be dropped > from a guest's cpuid in this case. Ok. > > > > > > There is nothing, as far as I can see, that says what will happen if the > > > condition is not met. I always interpreted it as undefined behaviour so > > > anything can happen including CPU dies completely. You are saying above > > > on one hand that CPU cannot handle any kinds of faults during write to > > > DS area, but on the other hand a guest could only crash itself. Is this > > > architecturally guarantied? > > > > You essentially would get random page faults, and the PEBS event will > > be cancelled. No hangs. > Is this a guest who will get those random page faults or a host? The guest (on the white listed CPU models) -Andi