From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751984AbbCKRgT (ORCPT ); Wed, 11 Mar 2015 13:36:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60006 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751821AbbCKRgR (ORCPT ); Wed, 11 Mar 2015 13:36:17 -0400 Date: Wed, 11 Mar 2015 18:34:09 +0100 From: Oleg Nesterov To: Dave Hansen , Borislav Petkov , Ingo Molnar Cc: Andy Lutomirski , Linus Torvalds , Pekka Riikonen , Rik van Riel , Suresh Siddha , LKML , "Yu, Fenghua" , Quentin Casasnovas Subject: [PATCH 1/4] x86/fpu: document user_fpu_begin() Message-ID: <20150311173409.GC5032@redhat.com> References: <54F74F59.5070107@intel.com> <20150311173346.GB5032@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150311173346.GB5032@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently user_fpu_begin() has a single caller and it is not clear that why do we actually need it, and why we should not worry about preemption right after preempt_enable(). Signed-off-by: Oleg Nesterov --- arch/x86/include/asm/fpu-internal.h | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-) diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h index 4bec98f..c615ae9 100644 --- a/arch/x86/include/asm/fpu-internal.h +++ b/arch/x86/include/asm/fpu-internal.h @@ -464,7 +464,9 @@ static inline int restore_xstate_sig(void __user *buf, int ia32_frame) * Need to be preemption-safe. * * NOTE! user_fpu_begin() must be used only immediately before restoring - * it. This function does not do any save/restore on their own. + * it. This function does not do any save/restore on its own. In a lazy + * fpu mode this is just optimization to avoid a dna fault, the task can + * lose FPU right after preempt_enable(). */ static inline void user_fpu_begin(void) { -- 1.5.5.1