linux-kernel - Re: Use of barriers in pvclock ABI

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:	Mon, 11 Aug 2008 17:15:04 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Gerd Hoffmann <kraxel@...hat.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Glauber de Oliveira Costa <glommer@...il.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kvm-devel <kvm@...r.kernel.org>
Subject: Re: Use of barriers in pvclock ABI

Gerd Hoffmann wrote:
>   Hi,
>
>   
>> However, the pvclock_clocksource_read() implementation is
>> over-engineered, because it checks for an odd version and uses very
>> strong rmb() barriers (which generates either an "lfence" or "lock add
>> $0, (%esp)").
>>
>> If we're happy to guarantee as an ABI issue that the record will never
>> be updated cross-cpu, then we can make the barriers simply barrier() and
>> just check for (src->version != dst->version).
>>
>> Is that OK with you, or do you want to leave open the possibility of
>> doing cross-cpu time updates?
>>     
>
> Due to the TSC being involved here I don't expect cross-cpu time updates
> will ever happen.  IMHO it is fine to change that.
>
>   

I agree.  And if we ever feel the need, we can allocate a feature bit 
for it.

-- 
error compiling committee.c: too many arguments to function

--
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/