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Tue, 15 Sep 2020 14:57:26 +0000 Subject: Re: [RFC PATCH 28/35] KVM: X86: Update kvm_skip_emulated_instruction() for an SEV-ES guest To: Sean Christopherson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, Paolo Bonzini , Jim Mattson , Joerg Roedel , Vitaly Kuznetsov , Wanpeng Li , Borislav Petkov , Ingo Molnar , Thomas Gleixner , Brijesh Singh References: <20200914215144.GE7192@sjchrist-ice> From: Tom Lendacky Message-ID: <8cbafd62-528d-fc8e-9945-575c2b659247@amd.com> Date: Tue, 15 Sep 2020 09:57:24 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: <20200914215144.GE7192@sjchrist-ice> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: DM5PR18CA0078.namprd18.prod.outlook.com (2603:10b6:3:3::16) To CY4PR12MB1352.namprd12.prod.outlook.com (2603:10b6:903:3a::13) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [10.236.30.118] (165.204.77.1) by DM5PR18CA0078.namprd18.prod.outlook.com (2603:10b6:3:3::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3370.16 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: fIrqqPk7vkzMWFiKKZQ+h7qLhMQbk1zWE1cDf6XRHJwveh4ad3iovDM86j07+8w7Ruj1VYlK/NilG16AHcCLBxe+qajN0S3/LhN554HhGhXqGj7Rjdeelg4RVNyja5l3Qz8l+KUSFvdtCEhnd7eMwwRI6gszpabQXXz+B9vp3EEXSlycOAdr6ZYWJ65Aj6yJCpX099aAkn9VVsOXyZvxowqz4rGKqHVpqc8uff1aCO0qc352oBcUF8WWt11zldIPvQpRwcExwz9VmcCbq0f9935bII9xJ8u9opyBVgnkNvIGoRNNxiF1lWFoDZcnQL2kCnOsWH6Q6//YsREmX9i8/DY7rnwe0Nw0weQT0W+dQfvyAgyEpnfN1qNOFxmYf9lhFBsImtY+rRYX8YTjkveK7djhnM0l5AxuExb9A/9ZsMxPKtnpeSddh+B6+qa56SieaJJdTTvDNYm0apeywqNHUbcj/324uGXSGkL7SrmQsSn6wSb1qXAfPwgKNvUaMDmhcJBAtbvFLrzn4fiSJsMouGWjBC3CBBFyuoLLSMgOyApoZNTzfvhNTTvSRAUHWwoVjV3yy5uenTr78pbQ6uVEAr1RPqGbJ85lPsJC1bka03WaW8HYuA+Krd6UyhR1BpUSGONtLZlwSTM374/L3rmKuw== X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 2fdd14bd-4f51-4c8b-2816-08d85987a8c0 X-MS-Exchange-CrossTenant-AuthSource: CY4PR12MB1352.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Sep 2020 14:57:26.2426 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: Vz0BjgTULaMYwRK1Fz5zEZAgxPqmVA31Rh9icNiXQUU96/sXeLjUIpGLQyb/YglwdkmHJ7MGWB0EyMKuJFvpOA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY4PR1201MB0152 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/14/20 4:51 PM, Sean Christopherson wrote: > On Mon, Sep 14, 2020 at 03:15:42PM -0500, Tom Lendacky wrote: >> From: Tom Lendacky >> >> The register state for an SEV-ES guest is encrypted so the value of the >> RIP cannot be updated. For an automatic exit, the RIP will be advanced >> as necessary. For a non-automatic exit, it is up to the #VC handler in >> the guest to advance the RIP. >> >> Add support to skip any RIP updates in kvm_skip_emulated_instruction() >> for an SEV-ES guest. > > Is there a reason this can't be handled in svm? E.g. can KVM be reworked > to effectively split the emulation logic so that it's a bug for KVM to end > up trying to modify RIP? > > Also, patch 06 modifies SVM's skip_emulated_instruction() to skip the RIP > update, but keeps the "svm_set_interrupt_shadow(vcpu, 0)" logic. Seems like > either that change or this one is wrong. I added this because of the get_rflags() call. But let me look into changing get_rflags() in svm.c and see if this patch can go away. Thanks, Tom > >> Signed-off-by: Tom Lendacky >> --- >> arch/x86/kvm/x86.c | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 23564d02d158..1dbdca607511 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -6874,13 +6874,17 @@ static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu) >> >> int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu) >> { >> - unsigned long rflags = kvm_x86_ops.get_rflags(vcpu); >> + unsigned long rflags; >> int r; >> >> r = kvm_x86_ops.skip_emulated_instruction(vcpu); >> if (unlikely(!r)) >> return 0; >> >> + if (vcpu->arch.vmsa_encrypted) >> + return 1; >> + >> + rflags = kvm_x86_ops.get_rflags(vcpu); >> /* >> * rflags is the old, "raw" value of the flags. The new value has >> * not been saved yet. >> -- >> 2.28.0 >>