From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966540Ab3DQOMo (ORCPT ); Wed, 17 Apr 2013 10:12:44 -0400 Received: from mail-bn1lp0151.outbound.protection.outlook.com ([207.46.163.151]:4343 "EHLO na01-bn1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S966321Ab3DQOMm convert rfc822-to-8bit (ORCPT ); Wed, 17 Apr 2013 10:12:42 -0400 X-Forefront-Antispam-Report-Untrusted: CIP:157.56.240.21;KIP:(null);UIP:(null);(null);H:BL2PRD0310HT001.namprd03.prod.outlook.com;R:internal;EFV:INT X-SpamScore: -2 X-BigFish: PS-2(zz98dI9371I542I1432Izz1f42h1fc6h1ee6h1de0h1fdah1202h1e76h1d1ah1d2ahzz17326ah8275bh8275dhz31h2a8h668h839h944hd24hf0ah1220h1288h12a5h12a9h12bdh137ah13b6h1441h1504h1537h153bh162dh1631h1758h18e1h1946h19b5h19ceh1ad9h1b0ah9a9j1155h) X-Forefront-Antispam-Report-Untrusted: SFV:SKI;SFS:;DIR:OUT;SFP:;SCL:-1;SRVR:SN2PR03MB061;H:SN2PR03MB061.namprd03.prod.outlook.com;LANG:en; From: KY Srinivasan To: "Michael S. Tsirkin" CC: "x86@kernel.org" , "gregkh@linuxfoundation.org" , "linux-kernel@vger.kernel.org" , "devel@linuxdriverproject.org" , "olaf@aepfle.de" , "apw@canonical.com" , "jasowang@redhat.com" , "tglx@linutronix.de" , "hpa@zytor.com" , "JBeulich@suse.com" , "bp@alien8.de" Subject: RE: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V Thread-Topic: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V Thread-Index: AQHOAnJoFJQhzmD3TUKsF9dq+4jlRZjabzYAgABndUD///hDAIAAE9LQ Date: Wed, 17 Apr 2013 14:12:12 +0000 Message-ID: <3b76ebfdb240419aa601309465a4c154@SN2PR03MB061.namprd03.prod.outlook.com> References: <1359940910-32114-1-git-send-email-kys@microsoft.com> <1359940959-32168-1-git-send-email-kys@microsoft.com> <1359940959-32168-2-git-send-email-kys@microsoft.com> <20130417070616.GA4487@redhat.com> <423ae84de75f4b3587eb2d1a365cbd95@SN2PR03MB061.namprd03.prod.outlook.com> <20130417124852.GD6801@redhat.com> In-Reply-To: <20130417124852.GD6801@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [98.110.61.163] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-OrganizationHeadersPreserved: SN2PR03MB061.namprd03.prod.outlook.com X-FOPE-CONNECTOR: Id%0$Dn%*$RO%0$TLS%0$FQDN%$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%LINUTRONIX.DE$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%REDHAT.COM$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%CANONICAL.COM$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%ALIEN8.DE$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%SUSE.COM$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%ZYTOR.COM$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%LINUXFOUNDATION.ORG$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%KERNEL.ORG$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%AEPFLE.DE$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%LINUXDRIVERPROJECT.ORG$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-FOPE-CONNECTOR: Id%59$Dn%VGER.KERNEL.ORG$RO%2$TLS%6$FQDN%corpf5vips-237160.customer.frontbridge.com$TlsDn% X-CrossPremisesHeadersPromoted: TK5EX14MLTC104.redmond.corp.microsoft.com X-CrossPremisesHeadersFiltered: TK5EX14MLTC104.redmond.corp.microsoft.com X-Forefront-Antispam-Report: CIP:131.107.125.37;CTRY:US;IPV:CAL;IPV:NLI;EFV:NLI;SFV:NSPM;SFS:(24454001)(199002)(189002)(377454001)(51704004)(13464002)(65816001)(80022001)(66066001)(5343655001)(59766001)(77982001)(79102001)(81542001)(51856001)(81342001)(76482001)(5343635001)(44976003)(69226001)(56816002)(16676001)(53806001)(15202345002)(23726002)(54356001)(33646001)(56776001)(54316002)(46406003)(47446002)(31966008)(49866001)(74662001)(46102001)(47736001)(47776003)(50466001)(63696002)(4396001)(47976001)(20776003)(6806003)(74502001)(50986001)(24736002);DIR:OUT;SFP:;SCL:1;SRVR:BL2FFO11HUB016;H:TK5EX14MLTC104.redmond.corp.microsoft.com;RD:InfoDomainNonexistent;A:1;MX:1;LANG:en; X-OriginatorOrg: microsoft.onmicrosoft.com X-Forefront-PRVS: 081904387B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Michael S. Tsirkin [mailto:mst@redhat.com] > Sent: Wednesday, April 17, 2013 8:49 AM > To: KY Srinivasan > Cc: x86@kernel.org; gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org; > devel@linuxdriverproject.org; olaf@aepfle.de; apw@canonical.com; > jasowang@redhat.com; tglx@linutronix.de; hpa@zytor.com; > JBeulich@suse.com; bp@alien8.de > Subject: Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V > > On Wed, Apr 17, 2013 at 01:20:58PM +0000, KY Srinivasan wrote: > > > > > > > -----Original Message----- > > > From: Michael S. Tsirkin [mailto:mst@redhat.com] > > > Sent: Wednesday, April 17, 2013 3:06 AM > > > To: KY Srinivasan > > > Cc: x86@kernel.org; gregkh@linuxfoundation.org; linux- > kernel@vger.kernel.org; > > > devel@linuxdriverproject.org; olaf@aepfle.de; apw@canonical.com; > > > jasowang@redhat.com; tglx@linutronix.de; hpa@zytor.com; > > > JBeulich@suse.com; bp@alien8.de > > > Subject: Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V > > > > > > On Sun, Feb 03, 2013 at 05:22:38PM -0800, K. Y. Srinivasan wrote: > > > > Xen emulates Hyper-V to host enlightened Windows. Looks like this > > > > emulation may be turned on by default even for Linux guests. Check and > > > > fail Hyper-V detection if we are on Xen. > > > > > > > > Signed-off-by: K. Y. Srinivasan > > > > > > I'm very curious what's the specific bug that is fixed here? > > > I went over the original discussion in > > > https://patchwork.kernel.org/patch/2064331/ > > > and that's still not clear to me. Is there a configuration > > > that is broken without this patch but starts working with > > > this patch? > > > > > > It seems that one might want to use hyper-v emulation e.g. to test > > > hyper-v code without using windows, so the functionality > > > that this patch disables is not completely useless, > > > so there should be a good reason for disabling it. > > > > > > Could you enlighten me please? :) > > > > Michael, > > > > If I recall correctly, the issue here was that Xen was enabling > > Hyper-V emulation un-conditionally even for Linux guests. > > Okay so basically some Xen specific strangeness. > > > Clearly, > > this was not the intention to begin with. This check was added to > > ensure that while hosting Linux we would not un-intentionally enable > > Hyper-V emulation in Xen. > > What if you want to intentionally enable Hyper-V emulation in Xen? > There's no way to do this now, right? > > > Not all Hyper-V features are tagged with a > > CPUID feature bit and so it was agreed that it would be better to > > disable Hyper-V emulation when hosting Linux on Xen. > > > > Regards, > > > > K. Y > > I was just asking whether there are any specific examples of a bug > or is this change done just in case? Ideally, if Hyper-V could be emulated in a plug compatible way, in that the guest would not know the difference as to whether Hyper-V was being emulated or indeed it was Hyper-V underneath, I would agree with you. Even in this case, I would argue that we would somehow give preference to the native implementation rather than the emulated environment. Having done the initial emulation of Hyper-V on Xen, I know the current emulation of Hyper-V is restricted to emulating a few features advertised via the CPUID bits. If I recall correctly, Xen did not implement the enlightened TLB flush scheme. Furthermore, none of the Hyper-V emulations implement the I/O related infrastructure. For Linux to run efficiently on Hyper-V, the I/O paths are significantly more important than what Hyper-V emulation there is in Xen and I suspect in KVM. So, I don't think we want to run Linux on Xen/KVM that is emulating Hyper-V (cpuids). The specific case I ran into that required this patch was when I moved the VMBUS interrupts to be delivered via a special hypervisor vector (to support full interrupt distribution amongst all VCPUs in the guest). This feature is not tagged in the CPUID feature bits and without this check, I would install an interrupt handler for the hypervisor vector that clearly did not make any sense in anything other than Hyper-V. I suspect there will be more such situations as we go forward. Regards, K. Y > > > > > > > > --- > > > > arch/x86/kernel/cpu/mshyperv.c | 7 +++++++ > > > > 1 files changed, 7 insertions(+), 0 deletions(-) > > > > > > > > diff --git a/arch/x86/kernel/cpu/mshyperv.c > > > b/arch/x86/kernel/cpu/mshyperv.c > > > > index 646d192..4dab317 100644 > > > > --- a/arch/x86/kernel/cpu/mshyperv.c > > > > +++ b/arch/x86/kernel/cpu/mshyperv.c > > > > @@ -30,6 +30,13 @@ static bool __init ms_hyperv_platform(void) > > > > if (!boot_cpu_has(X86_FEATURE_HYPERVISOR)) > > > > return false; > > > > > > > > + /* > > > > + * Xen emulates Hyper-V to support enlightened Windows. > > > > + * Check to see first if we are on a Xen Hypervisor. > > > > + */ > > > > + if (xen_cpuid_base()) > > > > + return false; > > > > + > > > > cpuid(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS, > > > > &eax, &hyp_signature[0], &hyp_signature[1], &hyp_signature[2]); > > > > > > > > -- > > > > 1.7.4.1 > > > > > > > > -- > > > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > > > the body of a message to majordomo@vger.kernel.org > > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > Please read the FAQ at http://www.tux.org/lkml/ > > > > > >