On 2/17/25 04:22, Nikunj A Dadhania wrote:
> Disallow writes to MSR_IA32_TSC for Secure TSC enabled SNP guests. Even if
> KVM attempts to emulate such writes, TSC calculation will ignore the
> TSC_SCALE and TSC_OFFSET present in the VMCB. Instead, it will use
> GUEST_TSC_SCALE and GUEST_TSC_OFFSET stored in the VMSA.
>
> Additionally, incorporate a check for protected guest state to allow the
> VMM to initialize the TSC MSR.
>
> Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
> ---
> arch/x86/kvm/svm/svm.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 93cf508f983c..7463466f5126 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3161,6 +3161,20 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
>
> svm->tsc_aux = data;
> break;
> + case MSR_IA32_TSC:
> + /*
> + * If Secure TSC is enabled, do not emulate TSC write as TSC calculation
> + * ignores the TSC_OFFSET and TSC_SCALE control fields, record the error
> + * and return a #GP. Allow the TSC to be initialized until the guest state
> + * is protected to prevent unexpected VMM errors.
> + */
> + if (vcpu->arch.guest_state_protected && snp_secure_tsc_enabled(vcpu->kvm)) {
I'm not sure if it matters, but do we need to differentiate between
guest and host write in this situation at all in regards to the message
or return code?
> + vcpu_unimpl(vcpu, "unimplemented IA32_TSC for secure tsc\n");
s/secure tsc/Secure TSC/ ?
Thanks,
Tom
> + return 1;
> + }
> +
> + ret = kvm_set_msr_common(vcpu, msr);
> + break;
> case MSR_IA32_DEBUGCTLMSR:
> if (!lbrv) {
> kvm_pr_unimpl_wrmsr(vcpu, ecx, data);
