linux-kernel - Re: [PATCH v15 09/13] tsc: Use the GUEST_TSC

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Message-ID: <cc8acb94-04e7-4ef3-a5a7-12e62a6c0b3d@amd.com>
Date: Thu, 2 Jan 2025 15:31:49 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: thomas.lendacky@....com, linux-kernel@...r.kernel.org, x86@...nel.org,
 kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
 dave.hansen@...ux.intel.com, pgonda@...gle.com, seanjc@...gle.com,
 pbonzini@...hat.com
Subject: Re: [PATCH v15 09/13] tsc: Use the GUEST_TSC_FREQ MSR for discovering
 TSC frequency

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