linux-kernel - Re: [RFC] perf: Clear MSRs on kexec

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 for Android: free password hash cracker in your pocket

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

Date:	Tue, 4 Aug 2015 07:52:29 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	Ingo Molnar <mingo@...nel.org>, dong.su@...csson.com,
	Vivek Goyal <vgoyal@...hat.com>,
	Haren Myneni <hbabu@...ibm.com>,
	Don Zickus <dzickus@...hat.com>
Subject: Re: [RFC] perf: Clear MSRs on kexec

On Mon, Aug 03, 2015 at 11:54:17PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 03, 2015 at 11:32:28PM +0200, Jiri Olsa wrote:
> > hi,
> > I'm getting following message on the kdump kernel start
> > 
> >   Broken BIOS detected, complain to your hardware vendor.\
> >   [Firmware Bug]: the BIOS has corrupted hw-PMU resources (MSR 38d is b0)
> > 
> > it seems to be caused by NMI watchdog being configured
> > and fixed counter values stays in MSRs, which triggers
> > warning in check_hw_exists and disables perf support
> > in kdump kernel.. which probably does not hurt ;-)
> > 
> > zeroing MSRs during kdump shutdown seems to work (attached)
> > but I'm not sure thats correct place for kdump perf callback
> 
> Right, but why bother? All that kernel needs to do is write a memory
> dump to someplace and reboot, right? The less you do, the less can go
> wrong.

well, I was hunting that 'Broken BIOS..' message which is wrong

I wouldn't think anyone wants to use perf under kdump kernel,
but you never know ;-)

jirka
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/