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Tue, 27 Jul 2021 16:51:23 +0000 From: Sunil Muthuswamy To: Michael Kelley , Praveen Kumar , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" CC: KY Srinivasan , Haiyang Zhang , Stephen Hemminger , "wei.liu@kernel.org" , Dexuan Cui , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "x86@kernel.org" , "hpa@zytor.com" , "viremana@linux.microsoft.com" , "nunodasneves@linux.microsoft.com" Subject: RE: [PATCH v3] hyperv: root partition faults writing to VP ASSIST MSR PAGE Thread-Topic: [PATCH v3] hyperv: root partition faults writing to VP ASSIST MSR PAGE Thread-Index: AQHXgtPz/n7CxiZ6zUi9GbDbsi36lqtXBSEAgAADfKA= Date: Tue, 27 Jul 2021 16:51:23 +0000 Message-ID: References: <20210727104044.28078-1-kumarpraveen@linux.microsoft.com> In-Reply-To: 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=bbb7c5d6-6379-42c3-a4ab-d20d2ffa5317;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=2021-07-27T16:17:48Z;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: MW4PR21MB2002.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: a85b7ce8-55ab-49e1-0d73-08d9511ec43f X-MS-Exchange-CrossTenant-originalarrivaltime: 27 Jul 2021 16:51:23.1557 (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: 5YQkzwKfDtILNgTXjZaf5kLcg9FoRPMDwbBxQZI1VmSDqhb3QuAmCBM/CIxZK4a5YEA2DkbpDtBWSXns2dgqCUITwoxWBLmNGBx8c2MGfbk= X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR21MB2074 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > > > - if (*hvp) { > > - u64 val; > > + WARN_ON(!(*hvp)); > > > > - val =3D vmalloc_to_pfn(*hvp); > > - val =3D (val << HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT) | > > - HV_X64_MSR_VP_ASSIST_PAGE_ENABLE; > > + if (*hvp) { > > + if (!hv_root_partition) > > + msr.guest_physical_address =3D vmalloc_to_pfn(*hvp); > > > > - wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, val); > > + msr.enable =3D 1; > > + wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, msr.as_uint64); >=20 > This version has a substantive difference compared with previous versions > in that the "enable" bit is being set and written back to the MSR even wh= en > running in the root partition. Is that intentional? Yes, the hypervisor won't allow the root to change the page address. So, to enable/disable it, the page address needs to be preserved and just the enab= le bit needs to be toggled. - Sunil