linux-kernel - Re: [PATCH v2] x86/intel: Fix always false range check in x86

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Message-ID: <CAO9wTFj1qCkhNG24hAWDfZqoJy4mhPFf6mKp=jg7GnaLmHix-w@mail.gmail.com>
Date: Tue, 29 Jul 2025 14:24:43 +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
Subject: Re: [PATCH v2] x86/intel: Fix always false range check in x86_vfm
 model matching

On Tue, 29 Jul 2025 at 13:26, Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Tue, Jul 29, 2025 at 12:23:27PM +0530, Suchit Karunakaran wrote:
> > On Tue, 29 Jul 2025 at 10:58, Greg KH <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Tue, Jul 29, 2025 at 09:56:21AM +0530, Suchit Karunakaran wrote:
> > > > Fix a logic bug in early_init_intel() where a conditional range check:
> > > > (c->x86_vfm >= INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_WILLAMETTE)
> > > > was always false due to (PRESCOTT) being numerically greater than the
> > > > upper bound (WILLAMETTE). This triggers:-Werror=logical-op:
> > > > logical ‘and’ of mutually exclusive tests is always false
> > > > The fix corrects the constant ordering to ensure the range is valid:
> > > > (c->x86_vfm >=  INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_CEDARMILL)
> > > >
> > > > Fixes: fadb6f569b10 ("x86/cpu/intel: Limit the non-architectural
> > > > constant_tsc model checks")
> > > >
> > > > Signed-off-by: Suchit Karunakaran <suchitkarunakaran@...il.com>
> > > >
> > > > Changes since v1:
> > > > - Fix incorrect logic
> > > > ---
> > > >  arch/x86/kernel/cpu/intel.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
> > > > index 076eaa41b8c8..6f5bd5dbc249 100644
> > > > --- a/arch/x86/kernel/cpu/intel.c
> > > > +++ b/arch/x86/kernel/cpu/intel.c
> > > > @@ -262,7 +262,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
> > > >       if (c->x86_power & (1 << 8)) {
> > > >               set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
> > > >               set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
> > > > -     } else if ((c->x86_vfm >= INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_WILLAMETTE) ||
> > > > +     } else if ((c->x86_vfm >=  INTEL_P4_PRESCOTT && c->x86_vfm <= INTEL_P4_CEDARMILL) ||
> > > >                  (c->x86_vfm >= INTEL_CORE_YONAH  && c->x86_vfm <= INTEL_IVYBRIDGE)) {
> > > >               set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
> > > >       }
> > > > --
> > > > 2.50.1
> > > >
> > > >
> > >
> > > Hi,
> > >
> > > This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
> > > a patch that has triggered this response.  He used to manually respond
> > > to these common problems, but in order to save his sanity (he kept
> > > writing the same thing over and over, yet to different people), I was
> > > created.  Hopefully you will not take offence and will fix the problem
> > > in your patch and resubmit it so that it can be accepted into the Linux
> > > kernel tree.
> > >
> > > You are receiving this message because of the following common error(s)
> > > as indicated below:
> > >
> > > - You have marked a patch with a "Fixes:" tag for a commit that is in an
> > >   older released kernel, yet you do not have a cc: stable line in the
> > >   signed-off-by area at all, which means that the patch will not be
> > >   applied to any older kernel releases.  To properly fix this, please
> > >   follow the documented rules in the
> > >   Documentation/process/stable-kernel-rules.rst file for how to resolve
> > >   this.
> > >
> > > If you wish to discuss this problem further, or you have questions about
> > > how to resolve this issue, please feel free to respond to this email and
> > > Greg will reply once he has dug out from the pending patches received
> > > from other developers.
> > >
> > > thanks,
> > >
> > > greg k-h's patch email bot
> >
> > Hi Greg,
> > I've a question regarding backporting this fix. Can this fix be
> > backported to stable kernel version 6.15.8? Also, should I send the
> > backport patch only after the initial patch has been merged in
> > mainline or linux-next?
>
> Did you read the document that my bot linked to above?  It should answer
> those questions :)
>
> thanks,
>
> greg k-h

Hi Greg,
I did go through the document you linked. I just wanted to clarify
about the backporting process, especially since the merge window has
already started and it might take some time for this to be merged into
mainline. Regardless, I'll send the backport patch after the initial
one has been merged.
Thanks again, and I apologize for any inconvenience.