From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCH v2 0/4] Expose HW APIC virtualization support to HVM guests Date: Tue, 11 Mar 2014 11:00:50 +0000 Message-ID: <531EECE2.2040709@citrix.com> References: <1394510043-3159-1-git-send-email-boris.ostrovsky@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1394510043-3159-1-git-send-email-boris.ostrovsky@oracle.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: Boris Ostrovsky Cc: keir@xen.org, jbeulich@suse.com, stefano.stabellini@eu.citrix.com, eddie.dong@intel.com, ian.jackson@eu.citrix.com, xen-devel@lists.xen.org, jun.nakajima@intel.com, ian.campbell@citrix.com List-Id: xen-devel@lists.xenproject.org On 11/03/14 03:53, Boris Ostrovsky wrote: > > Version 2: > * Added ability to specify hypervisor CPUID leaves in config file (this requires > new sysctl) > * Use 2 bits to indicate what is supported --- one for APIC memory access and the > other for x2APIC. Still not sure whether virtual interrupt delivery should be > exposed as well. > > > > HVM guests running on HW that supports HW APIC virtualization features > (APIC-register virtualization, virtual interrupt delivery, etc) may > want to use APIC instead of hvm_pirqs. Since we are not guaranteed to > have these features on VMX (for example, there is a boot option to > turn it off) and there is no such support on SVM we need to make the > guest aware that its APIC accesses may not be so bad. > > CPUID seems to be a good way to provide this info to the guest. It's seems a bit odd to use a Xen-specific (?) CPUID leaf to report that the guest should use a bare-metal feature -- that's the default behaviour of a HVM guest. I think it makes more sense to hint that the guest that a PV alternate is available and then omit this hint if using a virtualized APIC performs better. David