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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id r11sm3308283edt.58.2021.01.28.09.41.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 Jan 2021 09:41:25 -0800 (PST) Subject: Re: [PATCH v14 08/13] KVM: VMX: Add a synthetic MSR to allow userspace VMM to access GUEST_SSP To: Yang Weijiang , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, sean.j.christopherson@intel.com, jmattson@google.com Cc: yu.c.zhang@linux.intel.com References: <20201106011637.14289-1-weijiang.yang@intel.com> <20201106011637.14289-9-weijiang.yang@intel.com> From: Paolo Bonzini Message-ID: Date: Thu, 28 Jan 2021 18:41:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20201106011637.14289-9-weijiang.yang@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 06/11/20 02:16, Yang Weijiang wrote: > Introduce a host-only synthetic MSR, MSR_KVM_GUEST_SSP so that the VMM > can read/write the guest's SSP, e.g. to migrate CET state. Use a > synthetic MSR, e.g. as opposed to a VCPU_REG_, as GUEST_SSP is subject > to the same consistency checks as the PL*_SSP MSRs, i.e. can share code. > > Co-developed-by: Sean Christopherson > Signed-off-by: Sean Christopherson > Signed-off-by: Yang Weijiang > --- > arch/x86/include/uapi/asm/kvm_para.h | 1 + > arch/x86/kvm/vmx/vmx.c | 14 ++++++++++++-- > 2 files changed, 13 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h > index 812e9b4c1114..5203dc084125 100644 > --- a/arch/x86/include/uapi/asm/kvm_para.h > +++ b/arch/x86/include/uapi/asm/kvm_para.h > @@ -53,6 +53,7 @@ > #define MSR_KVM_POLL_CONTROL 0x4b564d05 > #define MSR_KVM_ASYNC_PF_INT 0x4b564d06 > #define MSR_KVM_ASYNC_PF_ACK 0x4b564d07 > +#define MSR_KVM_GUEST_SSP 0x4b564d08 > > struct kvm_steal_time { > __u64 steal; > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index dd78d3a79e79..28ba8414a7a3 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -1817,7 +1817,8 @@ static bool cet_is_ssp_msr_accessible(struct kvm_vcpu *vcpu, > if (msr->host_initiated) > return true; > > - if (!guest_cpuid_has(vcpu, X86_FEATURE_SHSTK)) > + if (!guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) || > + msr->index == MSR_KVM_GUEST_SSP) > return false; > > if (msr->index == MSR_IA32_INT_SSP_TAB) > @@ -1995,6 +1996,11 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > return 1; > msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE); > break; > + case MSR_KVM_GUEST_SSP: > + if (!cet_is_ssp_msr_accessible(vcpu, msr_info)) > + return 1; > + msr_info->data = vmcs_readl(GUEST_SSP); > + break; > case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP: > if (!cet_is_ssp_msr_accessible(vcpu, msr_info)) > return 1; > @@ -2287,12 +2293,16 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > return 1; > vmcs_writel(GUEST_INTR_SSP_TABLE, data); > break; > + case MSR_KVM_GUEST_SSP: > case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP: > if (!cet_is_ssp_msr_accessible(vcpu, msr_info)) > return 1; > if ((data & GENMASK(2, 0)) || is_noncanonical_address(data, vcpu)) > return 1; > - vmx_set_xsave_msr(msr_info); > + if (msr_index == MSR_KVM_GUEST_SSP) > + vmcs_writel(GUEST_SSP, data); > + else > + vmx_set_xsave_msr(msr_info); > break; > case MSR_TSC_AUX: > if (!msr_info->host_initiated && > Better make this fail if !msr_info->host_initiated. Paolo