Messages in this thread | | | Date | Wed, 24 May 2023 10:55:15 +0800 | Subject | Re: [PATCH v3 14/21] KVM:VMX: Add a synthetic MSR to allow userspace to access GUEST_SSP | From | "Yang, Weijiang" <> |
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On 5/23/2023 4:57 PM, Binbin Wu wrote: > > > 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?
No, when the access is initiated from host side, kvm_cet_is_msr_accessible() return true for MSR_KVM_GUEST_SSP.
So the code is reachable:
if (msr->host_initiated)
return true;
[...]
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