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Tue, 3 Jan 2023 03:32:53 +0000 Received: from DS0PR11MB6373.namprd11.prod.outlook.com ([fe80::97ed:f538:dc6a:a9c4]) by DS0PR11MB6373.namprd11.prod.outlook.com ([fe80::97ed:f538:dc6a:a9c4%6]) with mapi id 15.20.5944.019; Tue, 3 Jan 2023 03:32:53 +0000 From: "Wang, Wei W" To: Chao Peng , "Qiang, Chenyi" CC: "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-api@vger.kernel.org" , "linux-doc@vger.kernel.org" , "qemu-devel@nongnu.org" , Paolo Bonzini , Jonathan Corbet , "Christopherson,, Sean" , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Arnd Bergmann , Naoya Horiguchi , Miaohe Lin , "x86@kernel.org" , "H . Peter Anvin" , "Hugh Dickins" , Jeff Layton , "J . Bruce Fields" , Andrew Morton , Shuah Khan , Mike Rapoport , Steven Price , "Maciej S . Szmigiero" , Vlastimil Babka , Vishal Annapurve , Yu Zhang , "Kirill A . Shutemov" , "Lutomirski, Andy" , "Nakajima, Jun" , "Hansen, Dave" , "ak@linux.intel.com" , "david@redhat.com" , "aarcange@redhat.com" , "ddutile@redhat.com" , "dhildenb@redhat.com" , Quentin Perret , "tabba@google.com" , Michael Roth , "Hocko, Michal" Subject: RE: [PATCH v10 2/9] KVM: Introduce per-page memory attributes Thread-Topic: [PATCH v10 2/9] KVM: Introduce per-page memory attributes Thread-Index: AQHZBhXu7Ax4+tqGyUuhRxsCPgD73q6DIGyAgAj77wCAAAbkkA== Date: Tue, 3 Jan 2023 03:32:53 +0000 Message-ID: References: <20221202061347.1070246-1-chao.p.peng@linux.intel.com> <20221202061347.1070246-3-chao.p.peng@linux.intel.com> <1c9bbaa5-eea3-351e-d6a0-cfbc32115c82@intel.com> <20230103013948.GA2178318@chaop.bj.intel.com> In-Reply-To: <20230103013948.GA2178318@chaop.bj.intel.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=intel.com; x-ms-publictraffictype: Email x-ms-traffictypediagnostic: DS0PR11MB6373:EE_|IA1PR11MB6420:EE_ x-ms-office365-filtering-correlation-id: 9892dbcc-5ac8-41c4-27df-08daed3b326d x-ld-processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr x-ms-exchange-senderadcheck: 1 x-ms-exchange-antispam-relay: 0 x-microsoft-antispam: BCL:0; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: DS0PR11MB6373.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 9892dbcc-5ac8-41c4-27df-08daed3b326d X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Jan 2023 03:32:53.0901 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: An4kFQjQKfSwR+EaL9uksgjxgsiXQbUhfGm1APkx92jw1MVtvSJ2RhCTYCSsLuxsO9fyThEfaBe3pboD2E0AGg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR11MB6420 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday, January 3, 2023 9:40 AM, Chao Peng wrote: > > Because guest memory defaults to private, and now this patch stores > > the attributes with KVM_MEMORY_ATTRIBUTE_PRIVATE instead of > _SHARED, > > it would bring more KVM_EXIT_MEMORY_FAULT exits at the beginning of > > boot time. Maybe it can be optimized somehow in other places? e.g. set > > mem attr in advance. >=20 > KVM defaults to 'shared' because this ioctl can also be potentially used = by > normal VMs and 'shared' sounds a value meaningful for both normal VMs and > confidential VMs.=20 Do you mean a normal VM could have pages marked private? What's the usage? (If all the pages are just marked shared for normal VMs, then why do we nee= d it) > As for more KVM_EXIT_MEMORY_FAULT exits during the > booting time, yes, setting all memory to 'private' for confidential VMs t= hrough > this ioctl in userspace before guest launch is an approach for KVM usersp= ace to > 'override' the KVM default and reduce the number of implicit conversions. Most pages of a confidential VM are likely to be private pages. It seems mo= re efficient (and not difficult to check vm_type) to have KVM defaults to "private" for = confidential VMs and defaults to "shared" for normal VMs.