linux-kernel - Re: [PATCH v3] x86/cpu/intel: Fix the constant

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Message-ID: <CAO9wTFihpoVsf-SZYn6yUhCSuN9cBXFGWeGegDsS1QHk4wS7-Q@mail.gmail.com>
Date: Wed, 30 Jul 2025 11:05:31 +0530
From: Suchit Karunakaran <suchitkarunakaran@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, hpa@...or.com, darwi@...utronix.de, 
	sohil.mehta@...el.com, peterz@...radead.org, ravi.bangoria@....com, 
	skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v3] x86/cpu/intel: Fix the constant_tsc model check for
 Pentium 4s

On Wed, 30 Jul 2025 at 10:22, Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Wed, Jul 30, 2025 at 09:56:17AM +0530, Suchit Karunakaran wrote:
> > The logic to synthesize constant_tsc for Pentium 4s (Family 15) is
> > wrong. Since INTEL_P4_PRESCOTT is numerically greater than
> > INTEL_P4_WILLAMETTE, the logic always results in false and never sets
> > X86_FEATURE_CONSTANT_TSC for any Pentium 4 model.
> > The error was introduced while replacing the x86_model check with a VFM
> > one. The original check was as follows:
> >         if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
> >                 (c->x86 == 0x6 && c->x86_model >= 0x0e))
> >                 set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
>
> What do you mean by "original check"?  Before the change that caused
> this, or what it should be?
>

Original check in this context refers to the change before the erroneous code.

> > Fix the logic to cover all Pentium 4 models from Prescott (model 3) to
> > Cedarmill (model 6) which is the last model released in Family 15.
> >
> > Fixes: fadb6f569b10 ("x86/cpu/intel: Limit the non-architectural constant_tsc model checks")
> >
> > Cc: <stable@...r.kernel.org> # v6.15
> >
> > Signed-off-by: Suchit Karunakaran <suchitkarunakaran@...il.com>
>
> Nit, no blank lines beween all of those last lines.  Hint, look at all
> of the patches on the mailing lists AND in the tree already, you have
> hundreds of thousands of examples here of how to format things :)
>

Sorry about it. Should I send a new version of the patch removing the
blank lines?