From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "H. Peter Anvin" Subject: [ 14/25] x86, fpu: correct the asm constraints for fxsave, unbreak mxcsr.daz Date: Thu, 8 Aug 2013 18:41:50 -0700 Message-Id: <20130809013652.257990969@linuxfoundation.org> In-Reply-To: <20130809013649.057678051@linuxfoundation.org> References: <20130809013649.057678051@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: "H.J. Lu" commit eaa5a990191d204ba0f9d35dbe5505ec2cdd1460 upstream. GCC will optimize mxcsr_feature_mask_init in arch/x86/kernel/i387.c: memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct)); asm volatile("fxsave %0" : : "m" (fx_scratch)); mask = fx_scratch.mxcsr_mask; if (mask == 0) mask = 0x0000ffbf; to memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct)); asm volatile("fxsave %0" : : "m" (fx_scratch)); mask = 0x0000ffbf; since asm statement doesn’t say it will update fx_scratch. As the result, the DAZ bit will be cleared. This patch fixes it. This bug dates back to at least kernel 2.6.12. Signed-off-by: H. Peter Anvin Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/i387.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -132,7 +132,7 @@ static void __cpuinit mxcsr_feature_mask clts(); if (cpu_has_fxsr) { memset(&fx_scratch, 0, sizeof(struct i387_fxsave_struct)); - asm volatile("fxsave %0" : : "m" (fx_scratch)); + asm volatile("fxsave %0" : "+m" (fx_scratch)); mask = fx_scratch.mxcsr_mask; if (mask == 0) mask = 0x0000ffbf;