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Mon, 16 Jun 2025 18:09:04 +0000 Message-ID: Date: Mon, 16 Jun 2025 13:09:01 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 4/6] target/i386: Add couple of feature bits in CPUID_Fn80000021_EAX To: "Dr. David Alan Gilbert" Cc: pbonzini@redhat.com, zhao1.liu@intel.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, davydov-max@yandex-team.ru References: Content-Language: en-US From: "Moger, Babu" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: PH7P220CA0125.NAMP220.PROD.OUTLOOK.COM (2603:10b6:510:327::18) To MW3PR12MB4553.namprd12.prod.outlook.com (2603:10b6:303:2c::19) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MW3PR12MB4553:EE_|DM6PR12MB4122:EE_ X-MS-Office365-Filtering-Correlation-Id: bbb76350-bc24-4471-8d48-08ddad00e0bc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024; X-Microsoft-Antispam-Message-Info: =?utf-8?B?NDlCa1k2dTRJeHd3a3JRSUtha3g2MGc0bmx6cVl2N0xtbFVrZXM3Unp6TXVo?= =?utf-8?B?b2FxRWhuQWlJZnBrSi9xVC9SNDJLZHFJbVNyQUoveDBxVnQzTzJ2SzFob05q?= =?utf-8?B?cHJ1b0F6MEZ2MGUvS0JGdXpKTmw4QWZ0cDNkakx1bThXRVBrR3orL0tONkxU?= =?utf-8?B?ekg0dzc3cW1FOWZzcW5rY1RTNVNWbFNCQTVTWm5lSzh5VFFETG9LcWcvanVR?= =?utf-8?B?OXZaQU82SFVvRlZzaTJnTzBVbnZ1dk53aEpHQ2h0cmc4ZjVibFpRWU5xeUNU?= =?utf-8?B?ZFQwbndwZGlHQWgyczYwNXpvN0RzWnZLVTVRWXgveGhtSTBsNG9mVk5xaEpt?= =?utf-8?B?TFJZY2o1Qm43TzNQNVBrQmJGa3QxaUlRZDVxdEwzeG1HdWRyWnRnUHpUcGlu?= =?utf-8?B?eDB5dml5RDZlZ0pEMUdWcUxXS2hUSzBaMnBTM2FqRnRMOHE5RVhFZGhNaDh6?= =?utf-8?B?MHdNeFZEcmtjN01jakN2bWNaLzFqa2FVaEZQa2N1ZURSbVErQkhzKzJDM2s2?= =?utf-8?B?RFRxRXR4ejc2NTdaRFUrU3F2dUxaOUNTRytpc1QwbnQ2bjdKMjJmT2lia2p2?= =?utf-8?B?WlpGWlBuQnNCMDNZdC8rSU5hY1ZJLzJ1TFVGUkI1K1dnYlRKN3A3ODN0aTBB?= =?utf-8?B?a0Z0eHhGdEhsbHovMUF6eU5ITHZKU1VxQTVDcnFXOWlTbkowckYzYzZ5ZjdU?= =?utf-8?B?a256a3FpN3VDa0xwVEFsRFI4cXphelFFZGRFaEpacUhGWjZBS3BWd1VUNUR2?= =?utf-8?B?L0ZDYWZGOFRyeitLdzR3MlFoSmFWbzhnVzE4M2VKc2JCclZORmdFaXk4ejls?= =?utf-8?B?OWtaNzV5Vm94L0hhZWRqVHUxREpUbS9YdVVwNzB4WFY0RG10VXFHSncxWDZx?= =?utf-8?B?ckFxdnBLdkVPd2ZkNElEVUpJOW1OS1VEUG9BMFZxdW1xMjhCbTEvbHdoNUJL?= =?utf-8?B?eXFmTW5yVTUvUXhTNXFjRUhIVUF0VzZwM1QvRC85ZFZGM1NncGNxUFdNY1dG?= =?utf-8?B?QU5uVTVJcG9xODBXSE9xL1RKRjE1eEFkcU5ZZmh2VFJ3NDdCdHRVYjRYQkZ5?= =?utf-8?B?WC9CT05venQyakhIMndBeHpBaThETTZVVXBIcHNQODdPK3lhR0lOOGUwQWhO?= =?utf-8?B?N3RHQ0VoSzlsZkE3Wml1N1RZZjNQWTZ0dVpDVGJJWmVrRXJGWlRNcEZaMDBz?= =?utf-8?B?SUhLTjZPZUl1SkhPV1pGbERmd3J3Y3B0M1ZjbG5aRlNTbXZ2azNRWjVkcTVi?= =?utf-8?B?VmtPaGdUNEc1MTFmN0U4bkZyR1Fmd3pBNnE1SEZIUnZhK0EvMTFpdkkwYlk5?= =?utf-8?B?NnBMNjJSMW5MYWsrWUx1NW05TUlPWS93QkkrWUxNQmxDTUVmUDZqMFNrSDhs?= =?utf-8?B?R0xPT0RHclBNckRjWXFsUk1CdERoeDBJSng1WDRldkxqQy9TSGY4SkY3amVN?= =?utf-8?B?RXU5czd3d0pKNVRpT0xtdUZ6R1d1cEFMZStIR2k3SUlSTHVtVGdrVTl3aURr?= =?utf-8?B?UEs3WU1zZUNidi93QWFHUjc2Vnl1a1NwZStVRG0yRk51RGtuL1A2Wkd1SnlK?= =?utf-8?B?UVF6WHViczF1ZDE0N2pjNWlYYjlBaUk2R1hLOFR5L2VObGZMcXU4NHBYM1l6?= =?utf-8?B?Z3NGcW5IaVZnQkU4ZGRhZ2dSVFpEcElTR2ZCZkk3cUJZanZGT0NWVGpkSG8v?= =?utf-8?B?SXhHUzJaZDFpT1NOWG9MUkF3K1Zmby9pN09mT1MzZmt6WXZDYXFJejljb2pY?= =?utf-8?B?RXB6OU1LSUVZOTNDTlc2RXZQUnVrREthREtNbktkbnJ5WEhwNmNoWElSTFJ6?= =?utf-8?B?QzdBb290ZFdES3RnQlZXSU51cVFJbW5xOVZUbEpYeGxSVlVaMWdNczkrcVJT?= =?utf-8?B?VTFpRFNhRGh4cTdHKzN1cWNtZnc5NmQ4bFQvd0NGNi9OcmF4YU5acmh4bmx0?= =?utf-8?Q?Wc0xpfSnNsw=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255; 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envelope-from=Babu.Moger@amd.com; helo=NAM12-DM6-obe.outbound.protection.outlook.com X-Spam_score_int: -39 X-Spam_score: -4.0 X-Spam_bar: ---- X-Spam_report: (-4.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.892, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: babu.moger@amd.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hi Dave, On 6/6/25 07:29, Dr. David Alan Gilbert wrote: > * Babu Moger (babu.moger@amd.com) wrote: >> Add CPUID bit indicates that a WRMSR to MSR_FS_BASE, MSR_GS_BASE, or >> MSR_KERNEL_GS_BASE is non-serializing amd PREFETCHI that the indicates >> support for IC prefetch. >> >> CPUID_Fn80000021_EAX >> Bit Feature description >> 20 Indicates support for IC prefetch. >> 1 FsGsKernelGsBaseNonSerializing. > > I'm curious about this: > a) Is this new CPUs are non-serialising on that write? > b) If so, what happens if you run existing kernels/firmware on them? > c) Bonus migration question; what happens if you live migrate from a host > that claims to be serialising to one that has the extra non-serialising > flag but is disabled in the emulated CPU model. Good question. After looking at the AMD64 Architecture Programmer’s Manual again, these writes have always been non-serializing. Behavior has not changed. We're just reporting it through CPUID now. This information likely isn’t being used anywhere. Let me know if you have any questions. -- Thanks Babu Moger