Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932914AbcDENv6 (ORCPT ); Tue, 5 Apr 2016 09:51:58 -0400 Received: from mail-oi0-f67.google.com ([209.85.218.67]:36571 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758766AbcDENv4 (ORCPT ); Tue, 5 Apr 2016 09:51:56 -0400 MIME-Version: 1.0 In-Reply-To: <1459837795-2588-2-git-send-email-bp@alien8.de> References: <1459837795-2588-1-git-send-email-bp@alien8.de> <1459837795-2588-2-git-send-email-bp@alien8.de> Date: Tue, 5 Apr 2016 09:51:55 -0400 Message-ID: Subject: Re: [PATCH 1/6] x86/fpu/regset: Use boot_cpu_has() From: Brian Gerst To: Borislav Petkov Cc: X86 ML , LKML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1647 Lines: 41 On Tue, Apr 5, 2016 at 2:29 AM, Borislav Petkov wrote: > From: Borislav Petkov > > fpregs_{g,s}et() are not sizzling-hot paths to justify the need for > static_cpu_has(). Use the normal boot_cpu_has() helper. > > Signed-off-by: Borislav Petkov > --- > arch/x86/kernel/fpu/regset.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c > index bc5e76c1d7c5..81422dfb152b 100644 > --- a/arch/x86/kernel/fpu/regset.c > +++ b/arch/x86/kernel/fpu/regset.c > @@ -278,7 +278,7 @@ int fpregs_get(struct task_struct *target, const struct user_regset *regset, > > fpu__activate_fpstate_read(fpu); > > - if (!static_cpu_has(X86_FEATURE_FPU)) > + if (!boot_cpu_has(X86_FEATURE_FPU)) > return fpregs_soft_get(target, regset, pos, count, kbuf, ubuf); > > if (!boot_cpu_has(X86_FEATURE_FXSR)) > @@ -309,7 +309,7 @@ int fpregs_set(struct task_struct *target, const struct user_regset *regset, > fpu__activate_fpstate_write(fpu); > fpstate_sanitize_xstate(fpu); > > - if (!static_cpu_has(X86_FEATURE_FPU)) > + if (!boot_cpu_has(X86_FEATURE_FPU)) > return fpregs_soft_set(target, regset, pos, count, kbuf, ubuf); > > if (!boot_cpu_has(X86_FEATURE_FXSR)) I think the general rule should be always use static_cpu_has() for runtime checks, since it reduces down to a single jmp/nop instruction after alternatives run. Even if it's not a hot path, it saves a bit of runtime memory. boot_cpu_has() is fine for run-once init code. -- Brian Gerst