From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Ostrovsky Subject: Re: [PATCH] x86/hvm: Provide list of emulated features in HVM CPUID leaf Date: Wed, 3 Feb 2016 09:46:30 -0500 Message-ID: <56B212C6.5070606@oracle.com> References: <1454455041-4647-1-git-send-email-boris.ostrovsky@oracle.com> <56B13A2F.3070209@citrix.com> <56B13C0E.5070905@oracle.com> <56B14733.4010905@citrix.com> <56B1BD9F.7050302@citrix.com> <56B20F02.7050702@oracle.com> <56B210A6.5030109@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <56B210A6.5030109@citrix.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: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , jbeulich@suse.com, keir@xen.org Cc: david.vrabel@citrix.com, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On 02/03/2016 09:37 AM, Andrew Cooper wrote: > On 03/02/16 14:30, Boris Ostrovsky wrote: >> >> One might say that in Linux we have APIC even for PV guests >> --- we provide PV APIC ops. That's what I am using as justification >> for stating that the HVMlite guest has APIC to force-set >> X86_FEATURE_APIC bit. So this is somewhat similar to what Andrew is >> proposing in his option#2 (quoted below for convenience): >> >> 2) Find a way of telling the Linux boot path "trust me - here is >> an APIC >> driver - dont go looking under the hood". Possibly by registering a >> cpuid pvop which re-inserts the APIC bit, although this is liable to >> cause the boot code to then inspect the APICBASE_MSR, which will >> cause >> it to blow up slightly later on. > PV guests currently have Xen's APIC leaked through despite not having > access to an APIC. What do you mean by "leaked through"? > As with the XSAVE leakage, this has become an > defacto part of the ABI despite being architecturally wrong. > > I expect PVOps Linux will blow up when run on older hardware which does > lack a real APIC, or one which is disabled in the BIOS. I didn't mean to say that we set X86_FEATURE_APIC for PV guests, it's only done for HVMlite. I don't think there is hardware with VT/SVM that doesn't have APIC. Besides, in Linux we have config XEN_PVHVM def_bool y depends on XEN && PCI && X86_LOCAL_APIC and HVMlite is considered PVHVM. -boris