Messages in this thread | | | Date | Tue, 23 May 2023 16:57:09 +0800 | Subject | Re: [PATCH v3 14/21] KVM:VMX: Add a synthetic MSR to allow userspace to access GUEST_SSP | From | Binbin Wu <> |
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On 5/11/2023 12:08 PM, 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 <sean.j.christopherson@intel.com> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> > Signed-off-by: Yang Weijiang <weijiang.yang@intel.com> > --- > arch/x86/include/uapi/asm/kvm_para.h | 1 + > arch/x86/kvm/vmx/vmx.c | 15 ++++++++++++--- > arch/x86/kvm/x86.c | 4 ++++ > 3 files changed, 17 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h > index 6e64b27b2c1e..7af465e4e0bd 100644 > --- a/arch/x86/include/uapi/asm/kvm_para.h > +++ b/arch/x86/include/uapi/asm/kvm_para.h > @@ -58,6 +58,7 @@ > #define MSR_KVM_ASYNC_PF_INT 0x4b564d06 > #define MSR_KVM_ASYNC_PF_ACK 0x4b564d07 > #define MSR_KVM_MIGRATION_CONTROL 0x4b564d08 > +#define MSR_KVM_GUEST_SSP 0x4b564d09 > > struct kvm_steal_time { > __u64 steal; > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 0ccaa467d7d3..72149156bbd3 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -2095,9 +2095,13 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > break; > case MSR_IA32_U_CET: > case MSR_IA32_PL3_SSP: > + case MSR_KVM_GUEST_SSP: > if (!kvm_cet_is_msr_accessible(vcpu, msr_info)) > return 1; > - kvm_get_xsave_msr(msr_info); > + if (msr_info->index == MSR_KVM_GUEST_SSP) > + msr_info->data = vmcs_readl(GUEST_SSP); According to the change of the kvm_cet_is_msr_accessible() below, kvm_cet_is_msr_accessible() will return false for MSR_KVM_GUEST_SSP, then this code is unreachable?
> + else > + kvm_get_xsave_msr(msr_info); > break; > case MSR_IA32_DEBUGCTLMSR: > msr_info->data = vmcs_read64(GUEST_IA32_DEBUGCTL); > @@ -2413,15 +2417,20 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > break; > case MSR_IA32_U_CET: > case MSR_IA32_PL3_SSP: > + case MSR_KVM_GUEST_SSP: > if (!kvm_cet_is_msr_accessible(vcpu, msr_info)) > return 1; > if (is_noncanonical_address(data, vcpu)) > return 1; > if (msr_index == MSR_IA32_U_CET && (data & GENMASK(9, 6))) > return 1; > - if (msr_index == MSR_IA32_PL3_SSP && (data & GENMASK(2, 0))) > + if ((msr_index == MSR_IA32_PL3_SSP || > + msr_index == MSR_KVM_GUEST_SSP) && (data & GENMASK(2, 0))) > return 1; > - kvm_set_xsave_msr(msr_info); > + if (msr_index == MSR_KVM_GUEST_SSP) > + vmcs_writel(GUEST_SSP, data); > + else > + kvm_set_xsave_msr(msr_info); > break; > case MSR_IA32_PERF_CAPABILITIES: > if (data && !vcpu_to_pmu(vcpu)->version) > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 2e3a39c9297c..baac6acebd40 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -13642,6 +13642,10 @@ bool kvm_cet_is_msr_accessible(struct kvm_vcpu *vcpu, struct msr_data *msr) > !guest_cpuid_has(vcpu, X86_FEATURE_IBT)) > return false; > > + /* The synthetic MSR is for userspace access only. */ > + if (msr->index == MSR_KVM_GUEST_SSP) > + return false; > + > if (msr->index == MSR_IA32_PL3_SSP && > !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK)) > return false;
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