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

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Message-ID: <54CAA973.4050401@linux.intel.com>
Date:	Thu, 29 Jan 2015 13:43:15 -0800
From:	Dave Hansen <dave.hansen@...ux.intel.com>
To:	Oleg Nesterov <oleg@...hat.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 01/29/2015 01:33 PM, Oleg Nesterov wrote:
> 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.

Yeah, that's true.  That would also explain why I haven't run in to this
at all in testing.

Ugh, fpu_save_init() says it isn't preempt safe anyway, so we shouldn't
be using it.

I'll send a fix.
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