linux-kernel - Re: [PATCH 1/2] x86/platform: Add a low priority low frequency NMI call chain

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170307074210.GA24782@gmail.com>
Date:   Tue, 7 Mar 2017 08:42:10 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Mike Travis <mike.travis@....com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, Don Zickus <dzickus@...hat.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Frank Ramsay <frank.ramsay@....com>,
        Russ Anderson <russ.anderson@....com>,
        Tony Ernst <tony.ernst@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/platform: Add a low priority low frequency NMI
 call chain


* Mike Travis <mike.travis@....com> wrote:

> Add a new NMI call chain that is called last after all other NMI handlers
> have been checked and did not "handle" the NMI.  This mimics the current
> NMI_UNKNOWN call chain except it eliminates the WARNING message about
> multiple NMI handlers registering on this call chain.
> 
> This call chain dramatically lowers the NMI call frequency when high
> frequency NMI tools are in use, notably the perf tools.  It is required
> for NMI handlers that cannot sustain a high NMI call rate without
> ramifications to the system operability.

So how about we just turn off that warning instead? I don't remember the last time 
it actually _helped_ us find any kernel or hardware bug - and it has caused tons 
of problems...

It's not like we warn about excess regular IRQs either - we either handle them or 
at most increase a counter somewhere. We could do the same for NMIs: introduce a 
counter somewhere that counts the number of seemingly unhandled NMIs.

But in any case, we should not spam the kernel log, neither with high, nor with 
low frequency.

Thanks,

	Ingo