linux-kernel - Re: [PATCH 01/16] math128: Introduce various 128bit primitives

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: <20121026094207.GA2179@gmail.com>
Date:	Fri, 26 Oct 2012 11:42:07 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Juri Lelli <juri.lelli@...il.com>, tglx@...utronix.de,
	mingo@...hat.com, rostedt@...dmis.org, oleg@...hat.com,
	fweisbec@...il.com, darren@...art.com, johan.eker@...csson.com,
	p.faure@...tech.ch, linux-kernel@...r.kernel.org,
	claudio@...dence.eu.com, michael@...rulasolutions.com,
	fchecconi@...il.com, tommaso.cucinotta@...up.it,
	nicola.manica@...i.unitn.it, luca.abeni@...tn.it,
	dhaval.giani@...il.com, hgu1972@...il.com,
	paulmck@...ux.vnet.ibm.com, raistlin@...ux.it,
	insop.song@...csson.com, liming.wang@...driver.com,
	jkacur@...hat.com, harald.gustafsson@...csson.com,
	vincent.guittot@...aro.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 01/16] math128: Introduce various 128bit primitives


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, 2012-10-26 at 11:24 +0200, Ingo Molnar wrote:
> 
> > So can we control this by restricting the users and avoiding 
> > the overflow?
> > 
> > A 2^64 result should be a *huge* amount of space already for 
> > just about anything.
> 
> I _think_ something like: dl_runtime * dl_deadline < U64_MAX, 
> might do that. The question is, is this constraint usable? 
> Simplified that boils down to about 4 seconds each, which 
> sounds pretty much ok for most people -- but such statements 
> usually come back to bite you (640kb anybody...).

We could constrain the precision, not the maximum value.

Having a 4 seconds hard limit is one thing, only having 10 nsecs 
precision at 40 seconds is another.

Then the introduction of 128 bit math would be purely optional 
and would address *that* limitation of precision, and only that 
limitation. That way we could gladly skip 128 bit math.

Thanks,

	Ingo
--
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/