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

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Message-ID: <20250102091722.GCZ3ZZosVREObWSfX_@fat_crate.local>
Date: Thu, 2 Jan 2025 10:17:22 +0100
From: Borislav Petkov <bp@...en8.de>
To: "Nikunj A. Dadhania" <nikunj@....com>
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 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.

So again: you need to explain exactly *why* you're doing stuff in patches
because I don't have a crystal ball and I don't have special capabilities of
reading people's minds. If I had those, I wouldn't be doing this.

And if you had read my reply properly you would've realized that this is not
really what I'm asking. I'm asking why you have to assign the *same* function
to both function pointers.

And if you had done some git archeology, you would've found this:

aa297292d708 ("x86/tsc: Enumerate SKL cpu_khz and tsc_khz via CPUID")

and then you would've been able to state that you can assign the same function
to both function ptrs because the difference between CPU base and TSC
frequency does not apply in this case.

But that's too much to ask, right? :-(

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette