Re: [PATCH v5 13/14] x86/tsc: Mark Secure TSC as reliable clocksource

Kirill A. Shutemov
2023-11-02T10:33:16Z

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?

--
Kiryl Shutsemau / Kirill A. Shutemov