Re: [PATCH v3 3/5] x86/microcode: Avoid any chance of MCE's during microcode update

From: Borislav Petkov <bp@alien8.de>
To: Ashok Raj <ashok.raj@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tony Luck <tony.luck@intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	LKML Mailing List <linux-kernel@vger.kernel.org>,
	X86-kernel <x86@kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Jacon Jun Pan <jacob.jun.pan@intel.com>
Subject: Re: [PATCH v3 3/5] x86/microcode: Avoid any chance of MCE's during microcode update
Date: Wed, 17 Aug 2022 16:19:40 +0200	[thread overview]
Message-ID: <Yvz4/ASoX4SiXbhp@zn.tnic> (raw)
In-Reply-To: <YvzfebgOWVKYLClJ@araj-dh-work>

On Wed, Aug 17, 2022 at 12:30:49PM +0000, Ashok Raj wrote:
> You will find out when system returns after reboot and hopefully wasn't
> promoted to a cold-boot which will loose MCE banks.

Not good enough!

This should issue a warning in dmesg that a potential MCE while update
is running would cause a lockup. That is if we don't disable MCE around
it.

If we decide to disable MCE, it should say shutdown.

> Meaning deal with the effect of a really rare MCE. Rather than trying to
> avoid it. Taking the MCE is more important than finishing the update,
> and loosing what the error signaled was trying to convey.

Right now I'm inclined to not do anything and warn of a potential rare
situation.

> > > Shutdown, shutdown.. There is only 1 MCE no matter how many CPUs you have.
> > 
> > Because all CPUs are executing the loop? Or how do you decide this?
> 
> Fatal errors signaled with PCC=1 in the MCAx.STATUS is *ALWAYS*

What does that have to do with

"There is only 1 MCE no matter how many CPUs you have."

?

That's bullsh*t. Especially if the machine can do LMCE.

> I'm waiting for the results. :-).  And if you feel we can merge the
> - Patch1 - bug fix 
> - Patch2 - min-rev id
> 
> I do have the comments from Ingo captured, but I'll wait for other comments
> before i resend just those 2 and we can leave the NMI handling to get more
> testing and review before we consider.

No, you need to go read Documentation/process/.

I'm tired of having to explain to you how the kernel development process
works. You send your set, wait for a week, collect feedback and then you
send a new revision.

Not hammer people with patchsets every day.

This is not how that works.

If someone's breathing down your neck lemme know - I'd like to talk to
him/her.

Ok?!

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette