Messages in this thread | | | Date | Wed, 17 Aug 2022 15:06:27 +0000 | From | Ashok Raj <> | Subject | Re: [PATCH v3 3/5] x86/microcode: Avoid any chance of MCE's during microcode update |
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On Wed, Aug 17, 2022 at 04:19:40PM +0200, Borislav Petkov wrote: > 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!
I probably misread your question.. are you suggesting we add some WARN when we initiate late_load? I thought you were asking if the HW must signal something and OS should log when an MCE happens if MCIP=1
> > 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.
Ok, that clarifies it.. "IF we choose to set MCIP=1, we should tell users that hell can break loose, get under the table" :-)
> > > 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.
Encouraging.. So I'll drop that patch from the list next time around.
> > > > > 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.
Well, not outlandish :)
LMCE is only for recoverable errors. When we have a fatal error, sometimes the signalling and consumption of poison are going in different directions. In order to minimize exposure of bad data from being consumed, *ALL* Intel processors have always broadcast fatal errors. This is the history behind why we broadcast.
BTW: This is all legacy behavior. Nothing should come as surprise.
LMCE is best effort. This is the current state.
Cheers, Ashok
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