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b=f+UfV4xQwcKg4We/YjoTScnibyUVHV5JVxt+O8lvs+3GeXgqB0tZFq5RdpMDdfTL58zDM3mcgeSjkcL4yt3xFn5LclFagiH7qfwYCcY0e5WCOh/CMQWlm+9M51jKgc50y+ds9B3zoOmUpEHnvWxZUvgye1s8ap6aWt5mAkzfi6E= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from DS0PR12MB6608.namprd12.prod.outlook.com (2603:10b6:8:d0::10) by LV3PR12MB9117.namprd12.prod.outlook.com (2603:10b6:408:195::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8137.18; Thu, 7 Nov 2024 03:33:35 +0000 Received: from DS0PR12MB6608.namprd12.prod.outlook.com ([fe80::b71d:8902:9ab3:f627]) by DS0PR12MB6608.namprd12.prod.outlook.com ([fe80::b71d:8902:9ab3:f627%3]) with mapi id 15.20.8114.028; Thu, 7 Nov 2024 03:33:35 +0000 Message-ID: <599c8b26-0a9c-4ed2-9e35-be51db27a6f4@amd.com> Date: Thu, 7 Nov 2024 09:03:22 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 03/14] x86/apic: Populate .read()/.write() callbacks of Secure AVIC driver To: "Melody (Huibo) Wang" , linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, Thomas.Lendacky@amd.com, nikunj@amd.com, Santosh.Shukla@amd.com, Vasant.Hegde@amd.com, Suravee.Suthikulpanit@amd.com, bp@alien8.de, David.Kaplan@amd.com, x86@kernel.org, hpa@zytor.com, peterz@infradead.org, seanjc@google.com, pbonzini@redhat.com, kvm@vger.kernel.org References: <20240913113705.419146-1-Neeraj.Upadhyay@amd.com> <20240913113705.419146-4-Neeraj.Upadhyay@amd.com> Content-Language: en-US From: Neeraj Upadhyay In-Reply-To: Content-Type: text/plain; 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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. > Sure, I will add some of this information in the comments. Thanks for the review! - Neeraj > Thanks, > Melody