linux-kernel - Re: [RFC PATCH 04/11] x86,fpu: defer FPU restore until return to userspace

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: <54B55BE7.1020107@redhat.com>
Date:	Tue, 13 Jan 2015 12:54:47 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	matt.fleming@...el.com, bp@...e.de, pbonzini@...hat.com,
	tglx@...utronix.de, luto@...capital.net
Subject: Re: [RFC PATCH 04/11] x86,fpu: defer FPU restore until return to
 userspace

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 01/13/2015 12:11 PM, Oleg Nesterov wrote:
> On 01/11, riel@...hat.com wrote:
>> 
>> Defer restoring the FPU state, if so desired, until the task
>> returns to userspace.
> 
> And I have another concern.
> 
> Afaocs with this patch the idle threads will run with TIF_LOAD_FPU
> set but without fpu.has_fpu.
> 
> This is fine by itself, but this (performance-wise) breaks
> kernel_fpu_begin() if use_eager_fpu() == T. Please see the
> changelog in 5187b28ff08249ab8a162e8 and note that this patch cc's
> @stable.
> 
> Yes, yes, even if I am right we should blame kernel_fpu_begin() and
> other eager_fpu oddities. I tried to start the cleanups/fixes in
> this area some time ago, but they were ignored.

I suppose we could make kernel_fpu_begin() explicitly point
the cpu's fpu pointer at a special value to indicate that
we are in the middle of a kernel_fpu_begin() / kernel_fpu_end()
session, and should not use the FPU from interrupt context
right now.

Does that seem a reasonable fix?

- -- 
All rights reversed
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQEcBAEBAgAGBQJUtVvmAAoJEM553pKExN6DmWsH/0V3+3LQBLbOvLVM3h4abS0y
1aI1OqCVzhK4PUChbFwRWsk8IryvGt81n9n9CvnRBOPAg/ZII/NWsWweAVlD4NyL
sqaQf8h/mdaUnjoOUzfUmZmhLGtnktMW2beBKfPRbp5ynlLhr0u+kmQ15W2yUio3
Bu/FIhS7THcv/vNBtUfiz6cAaZZGDVrDXGIzxmNSIDTm7tibboZL2VfFI1AjQ+Mw
K0iH1tvG1E7n95krapnXHv8GlnzIFgd4yVe8jrLoV4i/045UZKWZbrY/az9VEi++
TFYzMbfJGtFc+MR4AUCed/g1zu2r1lIBNqpjf1GYu/qgJAzF9G07akZnUcITONA=
=Vg2Z
-----END PGP SIGNATURE-----
--
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/