linux-kernel - Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods

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: <4A36A1C7.6080005@zytor.com>
Date:	Mon, 15 Jun 2009 12:32:23 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, mingo@...hat.com,
	paulus@...ba.org, acme@...hat.com, linux-kernel@...r.kernel.org,
	penberg@...helsinki.fi, vegard.nossum@...il.com, efault@....de,
	jeremy@...p.org, npiggin@...e.de, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain	support
 to use NMI-safe methods

Mathieu Desnoyers wrote:
>>>
>> Writing control registers is serializing, so it's a lot more expensive
>> than writing a normal register; my *guess* is that it will be on the
>> order of 100-200 cycles.
>>
>> That is not based on any actual information.
>>
> 
> Then how about just writing to the cr2 register *if* it has changed
> while the NMI handler was running ?
> 
> if (unlikely(read_cr2() != saved_cr2)))
> 	write_cr2(saved_cr2)
> 
> Mathieu
> 

That works fine, obviously, and although it's probably overkill it's
also a trivially cheap optimization.

	-hpa

--
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/