linux-kernel - Re: [PATCH 0/3]: x86, fpu: unlazy

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Date:	Thu, 29 Jan 2015 22:33:46 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	Rik van Riel <riel@...hat.com>, Suresh Siddha <sbsiddha@...il.com>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3]: x86, fpu: unlazy_fpu fixes/cleanups

On 01/29, Dave Hansen wrote:
>
> On 01/29/2015 01:07 PM, Oleg Nesterov wrote:
> > On 01/23, Rik van Riel wrote:
> >> > Not only is this broken with my new code, but it looks like it may
> >> > be broken with the current code, too...
> > Lets (try to) fix unlazy_fpu/save_init_fpu at least.
> >
> > Dave, fpu_save_init() in do_bounds() and task_get_bounds_dir() looks
> > wrong too, shouldn't it use unlazy_fpu() ? See the changelog in 3/3.
>
> IIRC, the 'cpu_has_xsaveopt' on the CPUs that support will MPX will
> enable eagerfpu.

unless eagerfpu=off? but this doesn't matter.

> It's a bit of an indirect way to avoid the WARN_ON()
> and probably needs a better comment.

I don't think it is safe to assume that current has FPU even if eagerfpu.
And note that Rik is working on patches which can change this rule.

Or I misunderstood?

Oleg.

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