Re: [PATCH v2] x86/intel: Fix always false range check in x86_vfm model matching

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jul 29, 2025 at 02:24:43PM +0530, Suchit Karunakaran wrote:
> On Tue, 29 Jul 2025 at 13:26, Greg KH <gregkh@linuxfoundation.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@linuxfoundation.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@gmail.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.

As the document states, a commit must be in Linus's tree first, before
we can consider it for any stable release.

thanks,

greg k-h