Synchronize XSS from the GHCB to KVM's internal tracking if the guest marks XSS as valid on a #VMGEXIT. Like XCR0, KVM needs an up-to-date copy of XSS in order to compute the required XSTATE size when emulating CPUID.0xD.0x1 for the guest. Treat the incoming XSS change as an emulated write, i.e. validatate the guest-provided value, to avoid letting the guest load garbage into KVM's tracking. Simply ignore bad values, as either the guest managed to get an unsupported value into hardware, or the guest is misbehaving and providing pure garbage. In either case, KVM can't fix the broken guest. Note, emulating the change as an MSR write also takes care of side effects, e.g. marking dynamic CPUID bits as dirty. Suggested-by: John Allen Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/sev.c | 3 +++ arch/x86/kvm/svm/svm.h | 1 + 2 files changed, 4 insertions(+) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 0cd77a87dd84..0cd32df7b9b6 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -3306,6 +3306,9 @@ static void sev_es_sync_from_ghcb(struct vcpu_svm *svm) if (kvm_ghcb_xcr0_is_valid(svm)) __kvm_set_xcr(vcpu, 0, kvm_ghcb_get_xcr0(ghcb)); + if (kvm_ghcb_xss_is_valid(svm)) + __kvm_emulate_msr_write(vcpu, MSR_IA32_XSS, kvm_ghcb_get_xss(ghcb)); + /* Copy the GHCB exit information into the VMCB fields */ exit_code = kvm_ghcb_get_sw_exit_code(ghcb); control->exit_code = lower_32_bits(exit_code); diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index a42e95883b45..10d764878bcc 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -942,5 +942,6 @@ DEFINE_KVM_GHCB_ACCESSORS(sw_exit_info_1) DEFINE_KVM_GHCB_ACCESSORS(sw_exit_info_2) DEFINE_KVM_GHCB_ACCESSORS(sw_scratch) DEFINE_KVM_GHCB_ACCESSORS(xcr0) +DEFINE_KVM_GHCB_ACCESSORS(xss) #endif -- 2.51.0.384.g4c02a37b29-goog