linux-kernel - Re: [RFC -tip] x86,apic -- reduce disable

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:	Wed, 8 Jul 2009 00:49:11 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Cyrill Gorcunov <gorcunov@...nvz.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yinghai Lu <yinghai@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC -tip] x86,apic -- reduce disable_apic usage

On Sun, 5 Jul 2009, H. Peter Anvin wrote:

> >  How do you set cpu_has_apic for systems with discrete local APICs?  The 
> > CPUID flag is not set in this case.
> > 
> 
> Well, should it be?  We do set flags when they're appropriate to us, and
> if the semantics are such as that is inappropriate we can set a custom bit.

 Hmm, that might simplify things here and there and the less special cases 
in code -- and thus effort needed -- for the discrete APIC, the better.  
I think there is no reason why it couldn't be done -- all the places which 
need version-specific APIC features have to check the LVR register anyway.  
And the availability of the APICBASE MSR has to be validated separately 
too as it comes with P6+ only.

 The only place which could care I believe is code to set X86_FEATURE_11AP 
-- this should obviously be disabled for the discrete APIC as it is now, 
as the chip does not suffer from the erratum and the workaround is costly 
performance-wise.  That piece of code would have to be checked -- I don't 
know what the order of setting of these bits would be and thus if one 
could affect the other.  The dependency would better be well documented 
then too -- my observation is the knowledge about the APIC subsystem among 
people typically only covers a narrow subset of implementations.

  Maciej
--
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/