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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by SJ1PEPF000023D0.mail.protection.outlook.com (10.167.244.4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8137.17 via Frontend Transport; Wed, 6 Nov 2024 19:20:54 +0000 Received: from [10.23.197.56] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Wed, 6 Nov 2024 13:20:51 -0600 Message-ID: Date: Wed, 6 Nov 2024 11:20:41 -0800 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 03/14] x86/apic: Populate .read()/.write() callbacks of Secure AVIC driver To: Neeraj Upadhyay , CC: , , , , , , , , , , , , , , , References: <20240913113705.419146-1-Neeraj.Upadhyay@amd.com> <20240913113705.419146-4-Neeraj.Upadhyay@amd.com> Content-Language: en-US From: "Melody (Huibo) Wang" In-Reply-To: <20240913113705.419146-4-Neeraj.Upadhyay@amd.com> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Nov 2024 19:20:54.3809 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ee9acaaa-a8eb-43c4-4ff0-08dcfe98226d X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF000023D0.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB7795 Hi Neeraj, On 9/13/2024 4:36 AM, Neeraj Upadhyay wrote: > The x2APIC registers are mapped at an offset within the guest APIC > backing page which is same as their x2APIC MMIO offset. Secure AVIC > adds new registers such as ALLOWED_IRRs (which are at 4-byte offset > within the IRR register offset range) and NMI_REQ to the APIC register > space. In addition, the APIC_ID register is writable and configured by > guest. > > Add read() and write() APIC callback functions to read and write x2APIC > registers directly from the guest APIC backing page. > > The default .read()/.write() callbacks of x2APIC drivers perform > a rdmsr/wrmsr of the x2APIC registers. When Secure AVIC is enabled, > these would result in #VC exception (for non-accelerated register > accesses). The #VC exception handler reads/write the x2APIC register > in the guest APIC backing page. Since this would increase the latency > of accessing x2APIC registers, the read() and write() callbacks of > Secure AVIC driver directly reads/writes to the guest APIC backing page. > I think this is important non-obvious information which should be in a comment in the code itself, not just in the commit message. Thanks, Melody