Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932952Ab3FEV5e (ORCPT ); Wed, 5 Jun 2013 17:57:34 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:37841 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932814Ab3FEVff (ORCPT ); Wed, 5 Jun 2013 17:35:35 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Pekka Riikonen , "H. Peter Anvin" Subject: [ 057/127] x86: Allow FPU to be used at interrupt time even with eagerfpu Date: Wed, 5 Jun 2013 14:33:44 -0700 Message-Id: <20130605213224.520257595@linuxfoundation.org> X-Mailer: git-send-email 1.8.3.rc0.20.gb99dd2e In-Reply-To: <20130605213217.966891866@linuxfoundation.org> References: <20130605213217.966891866@linuxfoundation.org> User-Agent: quilt/0.60-5.1.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3614 Lines: 94 3.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Pekka Riikonen commit 5187b28ff08249ab8a162e802209ed04e271ca02 upstream. With the addition of eagerfpu the irq_fpu_usable() now returns false negatives especially in the case of ksoftirqd and interrupted idle task, two common cases for FPU use for example in networking/crypto. With eagerfpu=off FPU use is possible in those contexts. This is because of the eagerfpu check in interrupted_kernel_fpu_idle(): ... * For now, with eagerfpu we will return interrupted kernel FPU * state as not-idle. TBD: Ideally we can change the return value * to something like __thread_has_fpu(current). But we need to * be careful of doing __thread_clear_has_fpu() before saving * the FPU etc for supporting nested uses etc. For now, take * the simple route! ... if (use_eager_fpu()) return 0; As eagerfpu is automatically "on" on those CPUs that also have the features like AES-NI this patch changes the eagerfpu check to return 1 in case the kernel_fpu_begin() has not been said yet. Once it has been the __thread_has_fpu() will start returning 0. Notice that with eagerfpu the __thread_has_fpu is always true initially. FPU use is thus always possible no matter what task is under us, unless the state has already been saved with kernel_fpu_begin(). [ hpa: this is a performance regression, not a correctness regression, but since it can be quite serious on CPUs which need encryption at interrupt time I am marking this for urgent/stable. ] Signed-off-by: Pekka Riikonen Link: http://lkml.kernel.org/r/alpine.GSO.2.00.1305131356320.18@git.silcnet.org Signed-off-by: H. Peter Anvin Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/i387.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -22,23 +22,19 @@ /* * Were we in an interrupt that interrupted kernel mode? * - * For now, with eagerfpu we will return interrupted kernel FPU - * state as not-idle. TBD: Ideally we can change the return value - * to something like __thread_has_fpu(current). But we need to - * be careful of doing __thread_clear_has_fpu() before saving - * the FPU etc for supporting nested uses etc. For now, take - * the simple route! - * * On others, we can do a kernel_fpu_begin/end() pair *ONLY* if that * pair does nothing at all: the thread must not have fpu (so * that we don't try to save the FPU state), and TS must * be set (so that the clts/stts pair does nothing that is * visible in the interrupted kernel thread). + * + * Except for the eagerfpu case when we return 1 unless we've already + * been eager and saved the state in kernel_fpu_begin(). */ static inline bool interrupted_kernel_fpu_idle(void) { if (use_eager_fpu()) - return 0; + return __thread_has_fpu(current); return !__thread_has_fpu(current) && (read_cr0() & X86_CR0_TS); @@ -78,8 +74,8 @@ void __kernel_fpu_begin(void) struct task_struct *me = current; if (__thread_has_fpu(me)) { - __save_init_fpu(me); __thread_clear_has_fpu(me); + __save_init_fpu(me); /* We do 'stts()' in __kernel_fpu_end() */ } else if (!use_eager_fpu()) { this_cpu_write(fpu_owner_task, NULL); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/