linux-kernel - Re: [PATCH/RFC] Math-emu kills the kernel on Athlon64 X2 II -- it's terminally broken

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: <Pine.LNX.4.64.0610030746260.3952@g5.osdl.org>
Date:	Tue, 3 Oct 2006 07:48:22 -0700 (PDT)
From:	Linus Torvalds <torvalds@...l.org>
To:	Andi Kleen <ak@...e.de>
cc:	Randy Dunlap <rdunlap@...otime.net>, akpm <akpm@...l.org>,
	Jesper Juhl <jesper.juhl@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC] Math-emu kills the kernel on Athlon64 X2 II -- it's
 terminally broken



On Tue, 3 Oct 2006, Andi Kleen wrote:
> 
> Actually I looked at the code more closely. It looks like kernel math
> emulation is much more broken. e.g. kernel_fpu_begin() is missing
> code and lots of other paths in i387 that need to check HAVE_HWFP don't.

No it's not.

kernel_fpu_begin() has the _one_ test that matters:

	if (thread->status & TS_USEDFPU) {

since if software emulation is on, nobody will ever have the TS_USEDFPU 
flag set.

> Fixing it properly would be much more work.

No. It's all fixed properly already.

The bug is simply on the newer FXSR paths - marking the FPU emulation 
broken is just stupid. 

		Linus
-
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/