linux-kernel - RE: [PATCH v3 5/6] x86/MCE: Save MCA control bits that get set in hardware

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Date:   Thu, 23 May 2019 20:00:33 +0000
From:   "Ghannam, Yazen" <Yazen.Ghannam@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     "Luck, Tony" <tony.luck@...el.com>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCH v3 5/6] x86/MCE: Save MCA control bits that get set in
 hardware

> -----Original Message-----
> From: Borislav Petkov <bp@...en8.de>
> Sent: Friday, May 17, 2019 3:02 PM
> To: Ghannam, Yazen <Yazen.Ghannam@....com>
> Cc: Luck, Tony <tony.luck@...el.com>; linux-edac@...r.kernel.org; linux-kernel@...r.kernel.org; x86@...nel.org
> Subject: Re: [PATCH v3 5/6] x86/MCE: Save MCA control bits that get set in hardware
> 
> 
> On Fri, May 17, 2019 at 07:49:10PM +0000, Ghannam, Yazen wrote:
> > > @@ -1569,7 +1575,13 @@ static void __mcheck_cpu_init_clear_banks(void)
> > >
> > >                 if (!b->init)
> > >                         continue;
> > > +
> > > +               /* Check if any bits are implemented in h/w */
> > >                 wrmsrl(msr_ops.ctl(i), b->ctl);
> > > +               rdmsrl(msr_ops.ctl(i), msrval);
> > > +
> > > +               b->init = !!msrval;
> > > +
> > Just a minor nit, but can we group the comment, RDMSR, and check
> > together? The WRMSR is part of normal operation and isn't tied to the
> > check.
> 
> Of course it is - that's the "throw all 1s at it" part :)
> 

I did a bit more testing and I noticed that writing "0" disables a bank with no way to reenable it.

For example:
1) Read bank10.
	a) Succeeds; returns "fffffffffffffff".
2) Write "0" to bank10.
	a) Succeeds; hardware register is set to "0".
	b) Hardware register is checked, and b->init=0.
3) Read bank10.
	a) Fails, because b->init=0.
4) Write non-zero value to bank10 to reenable it.
	a) Fails, because b->init=0.
5) Reboot needed to reset bank.

Is that okay?

Thanks,
Yazen