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Dadhania wrote: >>> On 3/11/2025 2:41 PM, Nikunj A. Dadhania wrote: >>>> On 3/10/2025 9:09 PM, Tom Lendacky wrote: >>>>> On 3/10/25 01:45, Nikunj A Dadhania wrote: >>>> >>>>>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c >>>>>> index 50263b473f95..b61d6bd75b37 100644 >>>>>> --- a/arch/x86/kvm/svm/sev.c >>>>>> +++ b/arch/x86/kvm/svm/sev.c >>>>>> @@ -2205,6 +2205,20 @@ static int snp_launch_start(struct kvm *kvm, struct kvm_sev_cmd *argp) >>>>>> >>>>>> start.gctx_paddr = __psp_pa(sev->snp_context); >>>>>> start.policy = params.policy; >>>>>> + >>>>>> + if (snp_secure_tsc_enabled(kvm)) { >>>>>> + u32 user_tsc_khz = params.desired_tsc_khz; >>>>>> + >>>>>> + /* Use tsc_khz if the VMM has not provided the TSC frequency */ >>>>>> + if (!user_tsc_khz) >>>>>> + user_tsc_khz = tsc_khz; >>>>>> + >>>>>> + start.desired_tsc_khz = user_tsc_khz; > > The code just below this clobbers kvm->arch.default_tsc_khz, which could already > have been set by userspace. Why? Either require params.desired_tsc_khz to match > kvm->arch.default_tsc_khz, or have KVM's ABI be that KVM stuffs desired_tsc_khz > based on kvm->arch.default_tsc_khz. I don't see any reason to add yet another > way to control TSC. Setting of the desired TSC frequency needs to be done during SNP_LAUNCH_START, while parsing of the tsc-frequency happens as part of the cpu common class, and kvm->arch.default_tsc_khz is set pretty late. Intially, I had planned using "-cpu model,tsc-frequency=<>", but couldn't find a way to get this parsed early during SNP_LAUNCH_START. Regards, Nikunj