linux-kernel - RE: [PATCH v4 5/8] x86/mce: Convert family/model mixed checks to VFM-based checks

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Message-ID: <CY8PR11MB71344CF097758F67C9336B85895A2@CY8PR11MB7134.namprd11.prod.outlook.com>
Date: Wed, 13 Nov 2024 12:10:31 +0000
From: "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>
To: Yazen Ghannam <yazen.ghannam@....com>
CC: "bp@...en8.de" <bp@...en8.de>, "Luck, Tony" <tony.luck@...el.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "Mehta, Sohil" <sohil.mehta@...el.com>,
	"nik.borisov@...e.com" <nik.borisov@...e.com>, "x86@...nel.org"
	<x86@...nel.org>, "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 5/8] x86/mce: Convert family/model mixed checks to
 VFM-based checks

Hi Yazen,

> From: Yazen Ghannam <yazen.ghannam@....com>
> [...]
> > @@ -1954,6 +1954,10 @@ static void apply_quirks_intel(struct
> > cpuinfo_x86 *c)  {
> >  	struct mce_bank *mce_banks = this_cpu_ptr(mce_banks_array);
> >
> > +	/* Older CPUs (prior to family 6) don't need quirks. */
> > +	if (c->x86_vfm < INTEL_PENTIUM_PRO)
> > +		return;
> > +
> 
> Is it possible for pre-"family 6" to get here?
> 
> Family 5 is "ancient" which has its own MCE init path. And I assume anything
> older doesn't support MCE/MCA. Is this correct?

Yes, there is an early return in __mcheck_cpu_ancient_init() for Family 5. 
However, this code explicitly indicates that "prior to families 6 don't need quirks"
and addresses concerns like:

   https://lore.kernel.org/all/dcfdba92-7004-413d-8011-12771636d11f@intel.com/

> >  	/*
> >  	 * SDM documents that on family 6 bank 0 should not be written
> >  	 * because it aliases to another special BIOS controlled @@ -1962,22
> > +1966,21 @@ static void apply_quirks_intel(struct cpuinfo_x86 *c)
> >  	 * Don't ignore bank 0 completely because there could be a
> >  	 * valid event later, merely don't write CTL0.
> >  	 */
> > -	if (c->x86 == 6 && c->x86_model < 0x1A &&
> this_cpu_read(mce_num_banks) > 0)
> > +	if (c->x86_vfm < INTEL_NEHALEM_EP &&
> this_cpu_read(mce_num_banks) >
> > +0)
> 
> The "> 0" is not needed, since mce_num_banks is unsigned int.

I don't get your point here. 
But it needs to check for the case where mce_num_banks == 0.

> Otherwise, looks good.
> 
> Reviewed-by: Yazen Ghannam <yazen.ghannam@....com>

Thanks!
-Qiuxu