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Tested SNP with and without Secure TSC, guest works as expected. > > v11: > - Shuffle code around so that snp_is_secure_tsc_enabled() doesn't need to > be exposed outside of sev.c. > - Explicitly modify the intercept for MSR_AMD64_GUEST_TSC_FREQ (paranoia is > cheap in this case). > - Trim the changelog for the GHCB version enforcement patch. > - Continue on with snp_launch_start() if default_tsc_khz is '0'. AFAICT, > continuing on doesn't put the host at (any moer) risk. [Kai] If I hack default_tsc_khz as '0', SNP guest kernel with SecureTSC spits out couple of warnings and finally panics: Persistent clock returned invalid value ------------[ cut here ]------------ Missing cycle counter and fallback timer; RNG entropy collection will consequently suffer. WARNING: CPU: 0 PID: 0 at drivers/char/random.c:931 random_init+0xe7/0xf0 RIP: 0010:random_init+0xe7/0xf0 Call Trace: start_kernel+0x5e9/0xb80 x86_64_start_reservations+0x18/0x30 x86_64_start_kernel+0xf5/0x140 common_startup_64+0x13e/0x141 ... WARNING: CPU: 0 PID: 0 at arch/x86/kernel/tsc.c:1464 determine_cpu_tsc_frequencies+0x118/0x120 CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G W 6.17.0-rc2-stsc+ #1063 PREEMPT(voluntary) RIP: 0010:determine_cpu_tsc_frequencies+0x118/0x120 Call Trace: tsc_init+0x2ba/0x430 x86_late_time_init+0x29/0x40 start_kernel+0x70b/0xb80 x86_64_start_reservations+0x18/0x30 x86_64_start_kernel+0xf5/0x140 common_startup_64+0x13e/0x141 ... Oops: divide error: 0000 [#1] SMP NOPTI CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G W 6.17.0-rc2-stsc+ #1063 PREEMPT(voluntary) Tainted: [W]=WARN Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS unknown 02/02/2022 RIP: 0010:pit_hpet_ptimer_calibrate_cpu+0x1be/0x410 Call Trace: determine_cpu_tsc_frequencies+0xc1/0x120 tsc_init+0x2ba/0x430 x86_late_time_init+0x29/0x40 start_kernel+0x70b/0xb80 x86_64_start_reservations+0x18/0x30 x86_64_start_kernel+0xf5/0x140 common_startup_64+0x13e/0x141 Regards, Nikunj