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

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Message-ID: <CAO9wTFg_jCUZ+DxXVDM11_715r6ALJ=HyRXkcBxhGrBUo4iVUg@mail.gmail.com>
Date: Tue, 29 Jul 2025 12:23:27 +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 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?