linux-kernel - Re: [PATCH] [15/58] i386: Rewrite sched

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:	Fri, 20 Jul 2007 17:14:16 +0200
From:	Andi Kleen <ak@...e.de>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	patches@...-64.org, linux-kernel@...r.kernel.org,
	Daniel Walker <dwalker@...sta.com>
Subject: Re: [PATCH] [15/58] i386: Rewrite sched_clock


> So if, after this, we run tsc_sched_clock() with an unstable TSC, we
> read a last_val containing the interrupt's MSB and the last_val LSB. It
> can particularity hurt if we are around a 32 bits overflow, because time
> could "jump" forward of about 1.43 seconds on a 3 GHz system.
> 
> So I guess we need synchronization on the fast path, and therefore using
> cmpxchg_local on x86_64

On x86-64 the 64bit write is atomic against interrupts.

You're right 32bit has a problem though. I'm not too happy about 
cmpxchg though because that wouldn't work on some CPUs.

I wonder if we can just get away with using a 32bit value on i386.
Just for the purpose of keeping the value monotonic it should be good
enough. Will think about it.

Thanks for the review.

-Andi

-
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/