From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1756671AbbCMT2v (ORCPT <rfc822;w@1wt.eu>);
	Fri, 13 Mar 2015 15:28:51 -0400
Received: from cantor2.suse.de ([195.135.220.15]:45756 "EHLO mx2.suse.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1754008AbbCMT2s (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Fri, 13 Mar 2015 15:28:48 -0400
Date: Fri, 13 Mar 2015 20:27:17 +0100
From: Borislav Petkov <bp@suse.de>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>, Ingo Molnar <mingo@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Pekka Riikonen <priikone@iki.fi>, Rik van Riel <riel@redhat.com>,
        Suresh Siddha <sbsiddha@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "Yu, Fenghua" <fenghua.yu@intel.com>,
        Quentin Casasnovas <quentin.casasnovas@oracle.com>
Subject: Re: [PATCH 4/4] x86/fpu: don't abuse drop_init_fpu() in
 flush_thread()
Message-ID: <20150313192717.GJ31998@pd.tnic>
References: <54F74F59.5070107@intel.com>
 <20150311173346.GB5032@redhat.com>
 <20150311173507.GF5032@redhat.com>
 <20150313105251.GD31998@pd.tnic>
 <20150313145542.GD21603@redhat.com>
 <20150313161958.GI31998@pd.tnic>
 <20150313162654.GA26453@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20150313162654.GA26453@redhat.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, Mar 13, 2015 at 05:26:54PM +0100, Oleg Nesterov wrote:
> > One example where drop_init_fpu() seems to make sense is
> > __kernel_fpu_end(): kernel is done with FPU and current was using the
> > FPU prior so let's restore it for the eagerfpu case.
> 
> No, no, this is another case or I misunderstood you.
> 
> __kernel_fpu_end() needs to restore FPU from current's fpu->state exactly
> because current used FPU prior. And that state was saved by __save_init_fpu()
> in __kernel_fpu_begin().

That's exactly what I mean. See: "... kernel is done with FPU and current was
using the FPU prior..."

:-D

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--