Re: [PATCH v15 09/13] tsc: Use the GUEST_TSC_FREQ MSR for discovering TSC frequency

Nikunj A. Dadhania
2025-01-02T10:02:05Z

On 1/2/2025 2:47 PM, Borislav Petkov wrote:
> On Thu, Jan 02, 2025 at 10:40:05AM +0530, Nikunj A. Dadhania wrote:
>> Again: As kvm-clock has over-ridden both the callbacks, SecureTSC needs to
>> override them with its own.
>
> Again?
>
> Where do you state this fact?
>
> Because I don't see it in the commit message:
>
> "Calibrating the TSC frequency using the kvmclock is not correct for
> SecureTSC enabled guests. Use the platform provided TSC frequency via the
> GUEST_TSC_FREQ MSR (C001_0134h)."
>
> Yes, you had this in your reply but that's not good enough.

Sure, how about the below:

For SecureTSC enabled guests, TSC frequency should be obtained from the platform
provided GUEST_TSC_FREQ MSR (C001_0134h). As paravirt clock(kvm-clock) has over-ridden
x86_platform.calibrate_cpu() and x86_platform.calibrate_tsc() callbacks,
SecureTSC needs to override them with its own callbacks.

Regards
Nikunj