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]
Message-ID: <20071114185340.GB2894@zaniah>
Date:	Wed, 14 Nov 2007 19:53:40 +0100
From:	Philippe Elie <phil.el@...adoo.fr>
To:	William Cohen <wcohen@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@....hp.com>, akpm@...l.org,
	Robert Richter <robert.richter@....com>, gregkh@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [perfmon] Re: [perfmon2] perfmon2 merge news

On Wed, 14 Nov 2007 at 10:44 +0000, Will Cohen wrote:

> Andi Kleen wrote:
> 
> >>One approach does not prevent the other. Assuming you allow cr4.pce, then 
> >>nothing prevents
> >>a self-monitoring thread from reading the counters directly. You'll just 
> >>get the
> >>lower 32-bit of it. So if you read frequently enough, you should not have 
> >>a problem.
> >
> >Hmm? RDPMC is 64bit.
> 
> There are a number of processors that have 32-bit counters such as the IBM 
> power processors. On many x86 processors the upper bits of the counter are 
> sign extended from the lower 32 bits. Thus, one can only assume the lower 
> 32-bit are available. Roll over of values is quite possible (<2 seconds of 
> cycle count), so additional work needs to be done to obtain a valid value.

On x86 they are sign-extended only on write, on read they are 40 bits wide
for intel, 48 bits for AMD.

BTW, isn't rdpmc only enable for ring 0 on linux ? I remember a patch
to disable it, dunno if it has been applied.

-- 
Phe

-
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

Powered by Openwall GNU/*/Linux Powered by OpenVZ