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client-ip=165.204.84.17; helo=satlexmb08.amd.com; pr=C Received: from satlexmb08.amd.com (165.204.84.17) by CO1PEPF000042A8.mail.protection.outlook.com (10.167.243.37) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9520.1 via Frontend Transport; Wed, 14 Jan 2026 14:08:42 +0000 Received: from SATLEXMB04.amd.com (10.181.40.145) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.17; Wed, 14 Jan 2026 08:03:41 -0600 Received: from satlexmb07.amd.com (10.181.42.216) 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, 14 Jan 2026 08:03:40 -0600 Received: from [172.31.177.37] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Wed, 14 Jan 2026 06:03:37 -0800 Message-ID: <2669381c-ddbf-4cb2-a770-8308cd5ff353@amd.com> Date: Wed, 14 Jan 2026 19:33:31 +0530 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: [PATCH v5 7/8] KVM: SVM: Add Page modification logging support To: "Huang, Kai" , "pbonzini@redhat.com" , "seanjc@google.com" CC: "thomas.lendacky@amd.com" , "kvm@vger.kernel.org" , "joao.m.martins@oracle.com" , "santosh.shukla@amd.com" , "bp@alien8.de" References: <20260105063622.894410-1-nikunj@amd.com> <20260105063622.894410-8-nikunj@amd.com> <3d89f9d545d5d8b4558b591201cae19ad4cfb285.camel@intel.com> Content-Language: en-US From: "Nikunj A. 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This method works but >> incurs overhead due to additional write faults for each dirty GFN. >> >> Implement support for the Page Modification Logging (PML) feature, a >> hardware-assisted method for efficient dirty logging. PML automatically >> logs dirty GPA[51:12] to a 4K buffer when the CPU sets NPT D-bits. Two new >> VMCB fields are utilized: PML_ADDR and PML_INDEX. The PML_INDEX is >> initialized to 511 (8 bytes per GPA entry), and the CPU decreases the >> PML_INDEX after logging each GPA. When the PML buffer is full, a >> VMEXIT(PML_FULL) with exit code 0x407 is generated. >> >> Disable PML for nested guests. >> >> PML is enabled by default when supported and can be disabled via the 'pml' >> module parameter. > > Nit: > > If a new version is needed, use imperative mode: > > Add a new module parameter to enable/disable PML, and enable it by  > default when supported. Ack > >> >> Signed-off-by: Nikunj A Dadhania > > It's a bit weird for me to review, but I did anyway and it seems fine to > me, so: Thank you for taking the time to review the patches and for the detailed feedback throughout this series. Your insights have been very helpful. > > Acked-by: Kai Huang > > One minor thing below ... > > [...] > >> @@ -748,12 +748,19 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm, >> V_NMI_BLOCKING_MASK); >> } >> >> - /* Copied from vmcb01. msrpm_base can be overwritten later. */ >> + /* Copied from vmcb01. msrpm_base/nested_ctl can be overwritten later. */ >> vmcb02->control.nested_ctl = vmcb01->control.nested_ctl; >> vmcb02->control.iopm_base_pa = vmcb01->control.iopm_base_pa; >> vmcb02->control.msrpm_base_pa = vmcb01->control.msrpm_base_pa; >> vmcb_mark_dirty(vmcb02, VMCB_PERM_MAP); >> >> + /* Disable PML for nested guest as the A/D update is emulated by MMU */ > > This comment isn't accurate to me. I think the key reason is, for L2 if > PML enabled the recorded GPA will be L2's GPA, but not L1's. > > Please update the comment if a new version is needed? How about the below: + /* + * Disable PML for nested guests. When L2 runs with PML enabled, the + * CPU logs L2 GPAs rather than L1 GPAs, breaking dirty page tracking + * for the L0 hypervisor. + */ Regards Nikunj