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:	Wed, 09 Jul 2008 17:23:43 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Mike Travis <travis@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Jack Steiner <steiner@....com>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses

Eric W. Biederman wrote:
> Jeremy Fitzhardinge <jeremy@...p.org> writes:
>
>   
>>> Which means that my idea of using the technique we use on x86_32 will not
>>>       
>> work.
>>
>> No, the compiler memory model we use guarantees that everything will be within
>> 2G of each other.  The linker will spew loudly if that's not the case.
>>     
>
> The per cpu area is at least theoretically dynamically allocated.  And we
> really want to put it in cpu local memory.    Which means on any reasonable
> NUMA machine the per cpu areas should be all over the box.
>   

Yes, but that doesn't matter in the slightest.  The effective address 
will be within 2G of the base; the base can be anywhere.

> So there is no guarantee that with an arbitrary 64bit address in %gs of anything.
>
> Grr.  Except you are correct.  We have to guarantee that the offsets we have
> chosen at compile time still work.  And we know all of the compile time offsets
> will be in the -2G range.  So they are all 32bit numbers.  Negative 32bit
> numbers to be sure.  That trivially leaves us with everything working except
> the nasty hard coded decimal 40.
>   

Right.

    J
--
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/

Powered by blists - more mailing lists