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

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Date:   Tue, 28 May 2019 01:28:50 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Ghannam, Yazen" <Yazen.Ghannam@....com>
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

On Thu, May 23, 2019 at 08:00:33PM +0000, Ghannam, Yazen wrote:
> 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?

Nope, that doesn't sound correct to me.

I guess the cleanest way to handle his properly would be to have a
function called something like __mcheck_cpu_init_banks() which gets
called in mcheck_cpu_init() after the quirks have run and then does the
final poking of the banks and sets b->init properly.

__mcheck_cpu_init_clear_banks() should then be renamed to
__mcheck_cpu_clear_banks() to denote that it only clears the banks and
would only do:

                if (!b->init)
                        continue;

                wrmsrl(msr_ops.ctl(i), b->ctl);
                wrmsrl(msr_ops.status(i), 0);

And then sprinkle some commenting to not forget the scheme again.

Yeah, this sounds clean to me but you guys might have a better idea...

Thx.

-- 
Regards/Gruss,
    Boris.

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