linux-kernel - [patch] x32, fpu: fix DNA exception during check

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Message-Id: <1309479572.2665.1372.camel@sbsiddha-MOBL3.sc.intel.com>
Date:	Thu, 30 Jun 2011 17:19:32 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: [patch] x32, fpu: fix DNA exception during check_fpu()

From: Suresh Siddha <suresh.b.siddha@...el.com>

Before check_fpu() is called, we have cr0.TS bit set and hence the floating
point code to check the FDIV bug was generating a DNA exception.

Use kernel_fpu_begin()/kernel_fpu_end() around the floating point
code to avoid this unnecessary device not available exception during
boot.

Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
---
 arch/x86/kernel/cpu/bugs.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 525514c..46674fb 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -62,6 +62,8 @@ static void __init check_fpu(void)
 		return;
 	}
 
+	kernel_fpu_begin();
+
 	/*
 	 * trap_init() enabled FXSR and company _before_ testing for FP
 	 * problems here.
@@ -80,6 +82,8 @@ static void __init check_fpu(void)
 		: "=m" (*&fdiv_bug)
 		: "m" (*&x), "m" (*&y));
 
+	kernel_fpu_end();
+
 	boot_cpu_data.fdiv_bug = fdiv_bug;
 	if (boot_cpu_data.fdiv_bug)
 		printk(KERN_WARNING "Hmm, FPU with FDIV bug.\n");


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