linux-kernel - Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock

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, 28 Oct 2015 13:15:37 -0700
From:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
To:	Alex Smith <alex@...x-smith.me.uk>
CC:	David Daney <ddaney.cavm@...il.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Markos Chandras <markos.chandras@...tec.com>,
	linux-mips <linux-mips@...ux-mips.org>,
	Alex Smith <alex.smith@...tec.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and
 clock_gettime()

On 10/28/2015 12:55 PM, Alex Smith wrote:
> On 28 October 2015 at 19:28, Leonid Yegoshin <Leonid.Yegoshin@...tec.com> wrote:
>> . 
> Clocksources are not per-CPU. If the CP0 counter is the current
> clocksource, then both the kernel and VDSO implementations of
> gettimeofday will read out the CP0 counter from whatever CPU they run
> on.

OK, it was an invalid example. Let's be specific - in case of different 
clock frequency in different CPUs it easy to adjust it in kernel via 
clocksource->read()/etc but it is impossible to adjust that in VDSO 
implementation.

And that can't be fixed easily without some-kind of "per-thread" data 
page for correct multipliers.

There are many problems with assumption that in all kind of MIPS cores 
R4K CP0_COUNT registers are in sync in different CPUs. Even current 
kernel has problems here but I think it is not excuse to mount more on it.

- Leonid.

--
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/