linux-kernel - Re: [PATCH] perf/x86/intel: ignore CondChgd bit to avoid false NMI handling

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]

Date:	Thu, 12 Jun 2014 09:37:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc:	acme@...nel.org, mingo@...hat.com, paulus@...ba.org, hpa@...or.com,
	tglx@...utronix.de, x86@...nel.org, linux-kernel@...r.kernel.org,
	matt@...sole-pimps.org
Subject: Re: [PATCH] perf/x86/intel: ignore CondChgd bit to avoid false NMI
 handling

On Thu, Jun 12, 2014 at 04:00:11PM +0900, HATAYAMA Daisuke wrote:
> Also, I checked cpuid on the system with Neharlem processor where I
> have never seen CondChg bit is set.
> 
> [root@...alhost ~]# ./cpuid -r
> CPU 0:
>    0x00000000 0x00: eax=0x0000000b ebx=0x756e6547 ecx=0x6c65746e edx=0x49656e69
>    0x00000001 0x00: eax=0x000206e6 ebx=0x40200800 ecx=0x00bce3bd edx=0xbfebfbff
> <snip>
>    0x0000000a 0x00: eax=0x07300403 ebx=0x00000044 ecx=0x00000000 edx=0x00000603
>                     ^^^^^^^^^^^^^^
> So, cpuid tells that CondChg bit is supported on this processor, too.

Yeah, I can't remember ever seeing that bit on nhm/wsm either. Weird
stuff that.

> > In any case, the proposed patch seems fine, just needs a better
> > changelog.
> > 
> 
> I see.
> 
> I'll write that the problem is that any NMI could be robbed by NMI
> watchdog explicitly. Now only patch title says this explicitly. This
> is your first comment.

Yeah, since that is the actual problem, its good to be clear on that.

> About CondChgd bit, I cannot write more than I see on actual
> system. If it's necessary to describe more about CondChgd bit, it
> would be appreciated if someone tell me more information about it.

I think we've found all 2 sentences the SDM has about that and unless
someone from Intel is going to come and explain why they wasted precious
silicon on this I suppose it will remain a mystery. No need to update on
that.

Content of type "application/pgp-signature" skipped