Re: [PATCH v3] x86/cpu/intel: Fix the constant_tsc model check for Pentium 4s

Suchit Karunakaran
2025-07-30T06:21:57Z

On Wed, 30 Jul 2025 at 11:25, Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Wed, Jul 30, 2025 at 11:05:31AM +0530, Suchit Karunakaran wrote:
> > On Wed, 30 Jul 2025 at 10:22, Greg KH <gregkh@linuxfoundation.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@vger.kernel.org> # v6.15
> > > >
> > > > Signed-off-by: Suchit Karunakaran <suchitkarunakaran@gmail.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?
>
> That's up to the maintainer(s) of this subsystem, if they want to
> manually edit the change or not. As it's the middle of the merge
> window, no one will probably be doing anything for another 2 weeks on it
> anyway, so just relax and see what happens :)
>
> thanks,
>
> greg k-h

Hi Greg,
Thank you for the clarification. I apologize for the mistakes and
appreciate your patience in reviewing.

Thanks,
Suchit