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Dadhania" Cc: Tom Lendacky , pbonzini@redhat.com, kvm@vger.kernel.org, santosh.shukla@amd.com, bp@alien8.de, isaku.yamahata@intel.com Content-Type: text/plain; charset="us-ascii" On Tue, Mar 11, 2025, Nikunj A. Dadhania wrote: > > > On 3/11/2025 8:22 PM, Sean Christopherson wrote: > > On Tue, Mar 11, 2025, Tom Lendacky wrote: > >> On 3/11/25 06:05, Nikunj A. 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. That's a QEMU problem, not a KVM problem, no?