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Dadhania wrote: >> >> >> On 8/20/2025 5:18 AM, Sean Christopherson wrote: >>> From: Nikunj A Dadhania >>> >>> @@ -2195,6 +2206,12 @@ 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_is_secure_tsc_enabled(kvm)) { >>> + WARN_ON_ONCE(!kvm->arch.default_tsc_khz); >> >> Any particular reason to drop the the following change: >> >> + if (WARN_ON(!kvm->arch.default_tsc_khz)) { >> + rc = -EINVAL; >> + goto e_free_context; >> + } > > Based on this conversation[*], both Kai and I expected KVM to let firmware deal > with the should-be-impossible situation. > > On Tue, Jul 8, 2025 at 9:15 PM Nikunj A. Dadhania wrote: > > On 7/8/2025 8:04 PM, Sean Christopherson wrote: > > > On Tue, Jul 08, 2025, Kai Huang wrote: > > >>>> Even some bug results in the default_tsc_khz being 0, will the > > >>>> SNP_LAUNCH_START command catch this and return error? > > >>> > > >>> No, that is an invalid configuration, desired_tsc_khz is set to 0 when > > >>> SecureTSC is disabled. If SecureTSC is enabled, desired_tsc_khz should > > >>> have correct value. > > >> > > >> So it's an invalid configuration that when Secure TSC is enabled and > > >> desired_tsc_khz is 0. Assuming the SNP_LAUNCH_START will return an error > > >> if such configuration is used, wouldn't it be simpler if you remove the > > >> above check and depend on the SNP_LAUNCH_START command to catch the > > >> invalid configuration? > > > > > > Support for secure TSC should depend on tsc_khz being non-zero. That way it'll > > > be impossible for arch.default_tsc_khz to be zero at runtime. Then KVM can WARN > > > on arch.default_tsc_khz being zero during SNP_LAUNCH_START. > > > > Sure. > > https://lore.kernel.org/all/c327df02-c2eb-41e7-9402-5a16aa211265@amd.com > >> >> As this is an unsupported configuration as per the SEV SNP Firmware ABI Specification: > > Right, but what happens if KVM manages to pass in '0' for the frequency? Does > SNP_LAUNCH_START fail? SNP_LAUNCH_START succeeds, and the guest kernel starts and panics during early boot [*] > If so, bailing from KVM doesn't seem to add any value. As firmware does not bail out, I had kept this check. RegardsNikunjhttps://lore.kernel.org/all/afcf9a0b-7450-4df7-a21b-80b56264fc15@amd.com