linux-kernel - Re: [PATCH] Make math_state_restore() save and restore the interrupt flag

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 for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 1 Feb 2014 17:59:00 -0800
From:	Suresh Siddha <sbsiddha@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Nate Eldredge <nate@...tsmathematics.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	stable <stable@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Maarten Baert <maarten-baert@...mail.com>,
	Jan Kara <jack@...e.cz>, George Spelvin <linux@...izon.com>,
	Pekka Riikonen <priikone@....fi>
Subject: Re: [PATCH] Make math_state_restore() save and restore the interrupt flag

On Sat, Feb 1, 2014 at 5:51 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Sat, Feb 1, 2014 at 5:47 PM, Suresh Siddha <sbsiddha@...il.com> wrote:
>>
>> So if the restore failed, we should do something like drop_init_fpu(),
>> which will restore init-state to the registers.
>>
>> for eager-fpu()  paths we don't use clts() stts() etc.
>
> Uhhuh. Ok.
>
> Why do we do that, btw? I think it would make much more sense to just
> do what I *thought* we did, and just make it a context-switch-time
> optimization ("let's always switch FP state"), not make it a huge
> semantic difference.

clts/stts is more costly and not all the state under xsave adhers to
cr0.TS/DNA rules.

did I answer your question?

thanks,
suresh
--
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/