Re: [PATCH] x86/mce: Use ZENx features for Zen IF quirk

[Yazen Ghannam]

On Mon, Aug 11, 2025 at 10:55:29PM +0200, Borislav Petkov wrote:
> On Mon, Aug 11, 2025 at 04:34:08PM -0400, Yazen Ghannam wrote:
> > diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> > index 4da4eab56c81..0ef164568077 100644
> > --- a/arch/x86/kernel/cpu/mce/core.c
> > +++ b/arch/x86/kernel/cpu/mce/core.c
> > @@ -1951,8 +1951,11 @@ static void apply_quirks_amd(struct cpuinfo_x86 *c)
> >  	if (c->x86 == 0x15 && c->x86_model <= 0xf)
> >  		mce_flags.overflow_recov = 1;
> >  
> > -	if (c->x86 >= 0x17 && c->x86 <= 0x1A)
> > -		mce_flags.zen_ifu_quirk = 1;
> > +	mce_flags.zen_ifu_quirk = cpu_feature_enabled(X86_FEATURE_ZEN1) ||
> > +				  cpu_feature_enabled(X86_FEATURE_ZEN2) ||
> > +				  cpu_feature_enabled(X86_FEATURE_ZEN3) ||
> > +				  cpu_feature_enabled(X86_FEATURE_ZEN4) ||
> > +				  cpu_feature_enabled(X86_FEATURE_ZEN5);
> 
> I was fearing this day would come where we'd need something like that and it
> would look gross. And it does.
> 
> Can't we simplify the quirk to do:
> 
> 	if (!m->cs)
> 		m->cs = regs->cs;
> 
> when X86_FEATURE_ZEN is set and that should be good enough if we squint our
> eyes hard enough...

The quirk doesn't apply to all Zen-based systems. Only the Zen 1-5 are
affected.

We could *not* do this patch if it's too ugly. The quirk would apply to
some systems that aren't affected. But this would be a NOP in practice.

> 
> m->cs on the fixed machines won't be 0 so it all just works...
> 
> -- 

I've been thinking that we could do away with some of these quirks if we
refactor a bit. I'll dust off a patch I have and send for RFC.

Thanks,
Yazen