On 11/2/2023 6:08 PM, Kirill A. Shutemov wrote: > On Thu, Nov 02, 2023 at 05:46:26PM +0530, Nikunj A. Dadhania wrote: >> On 11/2/2023 5:37 PM, Nikunj A. Dadhania wrote: >>> On 11/2/2023 4:03 PM, Kirill A. Shutemov wrote: >>>> On Thu, Nov 02, 2023 at 11:23:34AM +0530, Nikunj A. Dadhania wrote: >>>>> On 10/30/2023 10:48 PM, Dave Hansen wrote: >>>>>> On 10/29/23 23:36, Nikunj A Dadhania wrote: >>>>>> ... >>>>>>> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c >>>>>>> index 15f97c0abc9d..b0a8546d3703 100644 >>>>>>> --- a/arch/x86/kernel/tsc.c >>>>>>> +++ b/arch/x86/kernel/tsc.c >>>>>>> @@ -1241,7 +1241,7 @@ static void __init check_system_tsc_reliable(void) >>>>>>> tsc_clocksource_reliable = 1; >>>>>>> } >>>>>>> #endif >>>>>>> - if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) >>>>>>> + if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE) || cc_platform_has(CC_ATTR_GUEST_SECURE_TSC)) >>>>>>> tsc_clocksource_reliable = 1; >>>>>> >>>>>> Why can't you just set X86_FEATURE_TSC_RELIABLE? >>>>> >>>>> Last time when I tried, I had removed my kvmclock changes and I had set >>>>> the X86_FEATURE_TSC_RELIABLE similar to Kirill's patch[1], this did not >>>>> select the SecureTSC. >>>>> >>>>> Let me try setting X86_FEATURE_TSC_RELIABLE and retaining my patch for >>>>> skipping kvmclock. >>>> >>>> kvmclock lowers its rating if TSC is good enough: >>>> >>>> if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && >>>> boot_cpu_has(X86_FEATURE_NONSTOP_TSC) && >>>> !check_tsc_unstable()) >>>> kvm_clock.rating = 299; >>>> >>>> Does your TSC meet the requirements? >>> >>> I have set TscInvariant (bit 8) in CPUID_8000_0007_edx and TSC is set as reliable. >>> >>> With this I see kvm_clock rating being lowered, but kvm-clock is still being picked as clock-source. >> >> Ah.. at later point TSC is picked up, is this expected ? >> >> [ 2.564052] clocksource: Switched to clocksource kvm-clock >> [ 2.678136] clocksource: Switched to clocksource tsc > > On bare metal I see switch from tsc-early to tsc. tsc-early rating is > equal to kvmclock rating after it gets lowered. For SNP guest with secure tsc enabled, kvm-clock and tsc-early both are at 299. Initially, kvm-clock is selected as clocksource and when tsc with 300 rating is enqueued, clocksource then switches to tsc. [ 0.004231] clocksource: clocksource_enqueue: name kvm-clock rating 299 [...] [ 2.046319] clocksource: clocksource_enqueue: name tsc-early rating 299 [...] [ 3.399179] clocksource: Switched to clocksource kvm-clock [...] [ 3.513652] clocksource: clocksource_enqueue: name tsc rating 300 [ 3.517314] clocksource: Switched to clocksource tsc > Maybe kvmclock rating has to be even lower after detecting sane TSC? If I set kvmclock rating to 298, I do see exact behavior as you have seen on the bare-metal. [ 0.004520] clocksource: clocksource_enqueue: name kvm-clock rating 298 [...] [ 1.827422] clocksource: clocksource_enqueue: name tsc-early rating 299 [...] [ 3.485059] clocksource: Switched to clocksource tsc-early [...] [ 3.623625] clocksource: clocksource_enqueue: name tsc rating 300 [ 3.628954] clocksource: Switched to clocksource tsc Regards Nikunj
