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Wed, 21 Jul 2021 04:10:33 +0000 From: Michael Kelley To: Wei Liu CC: Praveen Kumar , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , KY Srinivasan , Haiyang Zhang , Stephen Hemminger , Dexuan Cui , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "x86@kernel.org" , "hpa@zytor.com" , "viremana@linux.microsoft.com" , Sunil Muthuswamy , "nunodasneves@linux.microsoft.com" Subject: RE: [PATCH] hyperv: root partition faults writing to VP ASSIST MSR PAGE Thread-Topic: [PATCH] hyperv: root partition faults writing to VP ASSIST MSR PAGE Thread-Index: AQHXfOKuCkOiUQ46GkaTOSxdT1kTAKtLuKKAgAAjIwCAAAKZAIAALFMggAAEVYCAAMG8YA== Date: Wed, 21 Jul 2021 04:10:33 +0000 Message-ID: References: <20210719185126.3740-1-kumarpraveen@linux.microsoft.com> <20210720112011.7nxhiy6iyz4gz3j5@liuwe-devbox-debian-v2> <20210720133514.lurmus2lgffcldnq@liuwe-devbox-debian-v2> <20210720162923.rsbl24v5lujbiddj@liuwe-devbox-debian-v2> In-Reply-To: <20210720162923.rsbl24v5lujbiddj@liuwe-devbox-debian-v2> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ActionId=733849db-e03c-49fa-bf60-1fc5317282fb;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ContentBits=0;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=true;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Method=Standard;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Name=Internal;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SetDate=2021-07-21T04:02:47Z;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SiteId=72f988bf-86f1-41af-91ab-2d7cd011db47; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: MWHPR21MB1593.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 87922433-d9b4-4411-2393-08d94bfd7c60 X-MS-Exchange-CrossTenant-originalarrivaltime: 21 Jul 2021 04:10:33.3471 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: nilfdhRSyl8T5UDbiq9QDsWPvftLp/XAWKHvNU1xJa2Tnv3CPFoazV+aCHMQzXgaCzds1kuZ8Z1j+U2rMlBL9UfFTd/vpwSQ3+lsmVfPcT0= X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR21MB1987 Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org From: Wei Liu Sent: Tuesday, July 20, 2021 9:29 AM >=20 > On Tue, Jul 20, 2021 at 04:20:44PM +0000, Michael Kelley wrote: > > From: Wei Liu Sent: Tuesday, July 20, 2021 6:35 AM > > > > > > On Tue, Jul 20, 2021 at 06:55:56PM +0530, Praveen Kumar wrote: > > > [...] > > > > > > > > > >> + if (hv_root_partition && > > > > >> + ms_hyperv.features & HV_MSR_APIC_ACCESS_AVAILABLE) { > > > > > > > > > > Is HV_MSR_APIC_ACCESS_AVAILABLE a root only flag? Shouldn't non-r= oot > > > > > kernel check this too? > > > > > > > > Yes, you are right. Will update this in v2. thanks. > > > > > > Please split adding this check to its own patch. > > > > > > Ideally one patch only does one thing. > > > > > > Wei. > > > > > > > I was just looking around in the Hyper-V TLFS, and I didn't see > > anywhere that the ability to set up a VP Assist page is dependent > > on HV_MSR_APIC_ACCESS_AVAILABLE. Or did I just miss it? >=20 > The feature bit Praveen used is wrong and should be fixed. >=20 > Per internal discussion this is gated by the AccessIntrCtrlRegs bit. >=20 > Wei. >=20 The AccessIntrCtrlRegs bit *is* HV_MSR_APIC_ACCESS_AVAILABLE. Both are defined as bit 4 of the Partition Privilege flags. :-) I don't know why the names don't line up. Even so, it's not clear to me that AccessIntrCtrlRegs has any bearing on the VP Assist page. I see this description of AccessIntrCtrlRegs: The partition has access to the synthetic MSRs associated with the APIC (HV_X64_MSR_EOI, HV_X64_MSR_ICR and HV_X64_MSR_TPR). If this flag is cleared, accesses to these MSRs results in a #GP fault if the MSR intercept is not installed. But maybe you have additional info that applies to the root partition that is not in the TLFS. Michael