Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752947AbcCJPWL (ORCPT ); Thu, 10 Mar 2016 10:22:11 -0500 Received: from mail-yw0-f177.google.com ([209.85.161.177]:34491 "EHLO mail-yw0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752516AbcCJPWJ (ORCPT ); Thu, 10 Mar 2016 10:22:09 -0500 MIME-Version: 1.0 In-Reply-To: <20160310145940.GB26708@pd.tnic> References: <20160310111935.GB13102@gmail.com> <20160310125610.GA26708@pd.tnic> <20160310145940.GB26708@pd.tnic> Date: Thu, 10 Mar 2016 17:22:08 +0200 Message-ID: Subject: Re: Got FPU related warning on Intel Quark during boot From: Andy Shevchenko To: Borislav Petkov Cc: Ingo Molnar , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , Andy Lutomirski , Fenghua Yu , Linus Torvalds , "H. Peter Anvin" , Thomas Gleixner , Andrew Morton , Dave Hansen , Oleg Nesterov , "Yu, Yu-cheng" 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: 2132 Lines: 76 On Thu, Mar 10, 2016 at 4:59 PM, Borislav Petkov wrote: > On Thu, Mar 10, 2016 at 03:31:43PM +0200, Andy Shevchenko wrote: >> Looks like it lacks that one. >> >> # grep -i fxsr /proc/cpuinfo; echo $? >> 1 > > Ok, so looking at where the warning comes from: > > [ 14.714533] WARNING: CPU: 0 PID: 823 at arch/x86/include/asm/fpu/internal.h:163 fpu__clear+0x8c/0x160 > > static inline void copy_kernel_to_fxregs(struct fxregs_state *fx) > { > int err; > > if (config_enabled(CONFIG_X86_32)) { > err = check_insn(fxrstor %[fx], "=m" (*fx), [fx] "m" (*fx)); > ^^^^^^^^^^^^^^^^^ > } else { > > ... > > /* Copying from a kernel buffer to FPU registers should never fail: */ > WARN_ON_FPU(err); > > > and the stacktrace is pretty clear: > > flush_thread > |-> fpu__clear(&tsk->thread.fpu); > |-> we are eager by default here: > > if (!use_eager_fpu() || !static_cpu_has(X86_FEATURE_FPU)) { > /* FPU state will be reallocated lazily at the first use. */ > fpu__drop(fpu); > } else { > > --> we're in that branch. > > copy_init_fpstate_to_fpregs(); > |-> copy_kernel_to_fxregs() > > > I think we should use FRSTOR on quark, i.e., copy_kernel_to_fregs(). > > Does this untested wild guess even work? > > --- > diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c > index dea8e76d60c6..bbafe5e8a1a6 100644 > --- a/arch/x86/kernel/fpu/core.c > +++ b/arch/x86/kernel/fpu/core.c > @@ -474,8 +474,11 @@ static inline void copy_init_fpstate_to_fpregs(void) > { > if (use_xsave()) > copy_kernel_to_xregs(&init_fpstate.xsave, -1); > - else > + else if (static_cpu_has(X86_FEATURE_FXSR)) > copy_kernel_to_fxregs(&init_fpstate.fxsave); > + else > + copy_kernel_to_fregs(&init_fpstate.fsave); > + Obviously redundant line, otherwise it indeed works Tested-by: Andy Shevchenko > } > > /* -- With Best Regards, Andy Shevchenko