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

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Message-ID: <8247f64e-316d-0eca-9e5d-0c63c7dfc862@igalia.com>
Date: Sun, 23 Mar 2025 16:21:44 -0300
From: "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To: Borislav Petkov <bp@...en8.de>
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 23/03/2025 15:14, Borislav Petkov wrote:
> 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.

This is great to hear - is there any starting point model that you know
AMD introduced/is introducing 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?
>

We don't know yet what's going on, some TSC skews reported eventually in
some machines, in a fleet - but "old" processors, Zen 1st gen.
Once things are more clear, definitely could provide a more mature
report of the issue.

Cheers,

Guilherme