From: Vitaly Kuznetsov Date: Tue, 16 Mar 2021 14:37:33 +0000 (+0100) Subject: KVM: x86: hyper-v: Limit guest to writing zero to HV_X64_MSR_TSC_EMULATION_STATUS X-Git-Tag: v5.12-rc4~17^2~11 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d2547cf59793168b564372d75620897416cbaf87;p=thirdparty%2Fkernel%2Flinux.git KVM: x86: hyper-v: Limit guest to writing zero to HV_X64_MSR_TSC_EMULATION_STATUS HV_X64_MSR_TSC_EMULATION_STATUS indicates whether TSC accesses are emulated after migration (to accommodate for a different host TSC frequency when TSC scaling is not supported; we don't implement this in KVM). Guest can use the same MSR to stop TSC access emulation by writing zero. Writing anything else is forbidden. Signed-off-by: Vitaly Kuznetsov Message-Id: <20210316143736.964151-2-vkuznets@redhat.com> Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c index 58fa8c0298673..eefb85b86fe84 100644 --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -1229,6 +1229,9 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data, hv->hv_tsc_emulation_control = data; break; case HV_X64_MSR_TSC_EMULATION_STATUS: + if (data && !host) + return 1; + hv->hv_tsc_emulation_status = data; break; case HV_X64_MSR_TIME_REF_COUNT: