linux-kernel - Re: [PATCH 4/5] x86/mce: Fix all mce notifiers to update the mce->handled bitmask

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Message-ID: <CALCETrVrL1Ps9ubAcKQykxTofn4hbkESBYE9H22Ws5Pis_vG+g@mail.gmail.com>
Date:   Thu, 13 Feb 2020 14:27:31 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] x86/mce: Fix all mce notifiers to update the
 mce->handled bitmask

On Thu, Feb 13, 2020 at 2:19 PM Luck, Tony <tony.luck@...el.com> wrote:
>
> On Thu, Feb 13, 2020 at 06:03:08PM +0100, Borislav Petkov wrote:
> > On Wed, Feb 12, 2020 at 12:46:51PM -0800, Tony Luck wrote:
> > > If the handler took any action to log or deal with the error, set
> > > a bit int mce->handled so that the default handler on the end of
> > > the machine check chain can see what has been done.
> > >
> > > [!!! What to do about NOTIFY_STOP ... any handler that returns this
> > > value short-circuits calling subsequent entries on the chain. In
> > > some cases this may be the right thing to do ... but it others we
> > > really want to keep calling other functions on the chain]
> >
> > Yes, we can kill that NOTIFY_STOP thing in the mce code since it is
> > nasty.
>
> Well, there are places where we want to keep NOTIFY_STOP.

I very very strongly disagree.

>
> 1) Default case for CEC.  We want it to "hide" the corrected error.
>    That was one of the main goals for CEC.  We've discussed cases
>    where CEC shouldn't hide (when internal threshold exceeded and
>    it tries to take a page offline ... probably something related to
>    CMCI storms ... though we didn't really come to any conclusion)

Then put this logic in do_machine_check() or in some sensible place
that it calls via some ops structure or directly.  Don't hide it in
some incomprehensible, possibly nondeterministic place in a notifier
chain.

> 2) Errata. Perhaps a vendor/platform specific function at the head
>    of the notify chain that weeds out errors that should never have
>    been reported.

No, do this before the notifier chain please.

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