linux-kernel - Re: [PATCH] x86/tsc: Add debugfs entry to mark TSC as unstable after boot

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Message-ID: <20250323181444.GCZ-BPlCAhtO7AIsS7@fat_crate.local>
Date: Sun, 23 Mar 2025 19:14:44 +0100
From: Borislav Petkov <bp@...en8.de>
To: "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org, mingo@...hat.com,
	dave.hansen@...ux.intel.com, kernel@...ccoli.net,
	kernel-dev@...lia.com
Subject: Re: [PATCH] x86/tsc: Add debugfs entry to mark TSC as unstable after
 boot

On Sun, Mar 23, 2025 at 02:53:05PM -0300, Guilherme G. Piccoli wrote:
> But what about AMD systems? Even the modern ones apparently lack
> TSC_ADJUST - or is it changing recently?

Yes, it is.

> Checking TSC code, it is full of checks "if Intel" as well, like in
> native calibration. Our issue is present on AMD and my impression is
> that, in this respect, these systems are way more unstable (from TSC
> perspective) than the ones having TSC_ADJUST.

The only one I know of is a Zen2 laptop where BIOS botches a perfectly fine
TSC because those BIOS programmers are soo smart.

If you know of other cases, where are those bug reports?

Thx.

-- 
Regards/Gruss,
    Boris.

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