linux-kernel - Re: ABI change for device drivers using future AVX instruction set

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:	Sat, 28 Jun 2008 17:09:19 +0200
From:	Agner Fog <agner@...er.org>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Arjan van de Ven <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: ABI change for device drivers using future AVX instruction set

Andi Kleen wrote:
 >If a x86 device driver doesn't use the standard kernel interfaces for 
saving/restoring extended state
 > (kernel_fpu_begin/end) it will die.That is because Linux uses lazy 
FPU saving by default and when the
 >lazy FPU exception hits kernel code it will crash because that's not 
allowed. And the standard interfaces
 >are going to handle all extended state supported by the kernel. Full 
XSAVE support should be there for
 > 2.6.27.

Thank you Andi. Finally an exact and exhaustive answer. :-)
This info is not in the "Unreliable Guide To Hacking The Linux Kernel" 
or anywhere else except deeply hidden in the archives of this mailing 
list. I had to actually look into the source code of kernel_fpu_begin to 
verify that it saves not only the FPU but also the XMM registers and 
that it disables pre-emption.

You see why I want proper documentation? If this had been documented in 
some reference that was easy to find, I wouldn't have needed to take 
your time with all these questions...

Note: Please Cc: me of answers.
--
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/