On 20/02/25 12:50, Xiaoyao Li wrote: > On 1/29/2025 5:58 PM, Adrian Hunter wrote: >> From: Sean Christopherson <seanjc@xxxxxxxxxx> >> >> Allow the use of kvm_load_host_xsave_state() with >> vcpu->arch.guest_state_protected == true. This will allow TDX to reuse >> kvm_load_host_xsave_state() instead of creating its own version. >> >> For consistency, amend kvm_load_guest_xsave_state() also. >> >> Ensure that guest state that kvm_load_host_xsave_state() depends upon, >> such as MSR_IA32_XSS, cannot be changed by user space, if >> guest_state_protected. >> >> [Adrian: wrote commit message] >> >> Link: https://lore.kernel.org/r/Z2GiQS_RmYeHU09L@xxxxxxxxxx >> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> >> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx> >> --- >> TD vcpu enter/exit v2: >> - New patch >> --- >> arch/x86/kvm/svm/svm.c | 7 +++++-- >> arch/x86/kvm/x86.c | 18 +++++++++++------- >> 2 files changed, 16 insertions(+), 9 deletions(-) >> >> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c >> index 7640a84e554a..b4bcfe15ad5e 100644 >> --- a/arch/x86/kvm/svm/svm.c >> +++ b/arch/x86/kvm/svm/svm.c >> @@ -4253,7 +4253,9 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, >> svm_set_dr6(svm, DR6_ACTIVE_LOW); >> clgi(); >> - kvm_load_guest_xsave_state(vcpu); >> + >> + if (!vcpu->arch.guest_state_protected) >> + kvm_load_guest_xsave_state(vcpu); >> kvm_wait_lapic_expire(vcpu); >> @@ -4282,7 +4284,8 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, >> if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI)) >> kvm_before_interrupt(vcpu, KVM_HANDLING_NMI); >> - kvm_load_host_xsave_state(vcpu); >> + if (!vcpu->arch.guest_state_protected) >> + kvm_load_host_xsave_state(vcpu); >> stgi(); >> /* Any pending NMI will happen here */ >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index bbb6b7f40b3a..5cf9f023fd4b 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -1169,11 +1169,9 @@ EXPORT_SYMBOL_GPL(kvm_lmsw); >> void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu) >> { >> - if (vcpu->arch.guest_state_protected) >> - return; >> + WARN_ON_ONCE(vcpu->arch.guest_state_protected); >> if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) { >> - >> if (vcpu->arch.xcr0 != kvm_host.xcr0) >> xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0); >> @@ -1192,13 +1190,11 @@ EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state); >> void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu) >> { >> - if (vcpu->arch.guest_state_protected) >> - return; >> - >> if (cpu_feature_enabled(X86_FEATURE_PKU) && >> ((vcpu->arch.xcr0 & XFEATURE_MASK_PKRU) || >> kvm_is_cr4_bit_set(vcpu, X86_CR4_PKE))) { >> - vcpu->arch.pkru = rdpkru(); >> + if (!vcpu->arch.guest_state_protected) >> + vcpu->arch.pkru = rdpkru(); > > this needs justification. It was proposed by Sean here: https://lore.kernel.org/all/Z2WZ091z8GmGjSbC@xxxxxxxxxx/ which is part of the email thread referenced by the "Link:" tag above > >> if (vcpu->arch.pkru != vcpu->arch.host_pkru) >> wrpkru(vcpu->arch.host_pkru); >> } > > >> @@ -3916,6 +3912,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) >> if (!msr_info->host_initiated && >> !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES)) >> return 1; >> + >> + if (vcpu->arch.guest_state_protected) >> + return 1; >> + > > this and below change need to be a separate patch. So that we can discuss independently. > > I see no reason to make MSR_IA32_XSS special than other MSRs. When guest_state_protected, most of the MSRs that aren't emulated by KVM are inaccessible by KVM. Yes, TDX will block access to MSR_IA32_XSS anyway because tdx_has_emulated_msr() will return false for MSR_IA32_XSS. However kvm_load_host_xsave_state() is not TDX-specific code and it relies upon vcpu->arch.ia32_xss, so there is reason to block access to it when vcpu->arch.guest_state_protected is true. > >> /* >> * KVM supports exposing PT to the guest, but does not support >> * IA32_XSS[bit 8]. Guests have to use RDMSR/WRMSR rather than >> @@ -4375,6 +4375,10 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) >> if (!msr_info->host_initiated && >> !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES)) >> return 1; >> + >> + if (vcpu->arch.guest_state_protected) >> + return 1; >> + >> msr_info->data = vcpu->arch.ia32_xss; >> break; >> case MSR_K7_CLK_CTL: >
