Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933344AbcCKBkA (ORCPT ); Thu, 10 Mar 2016 20:40:00 -0500 Received: from mail-ob0-f174.google.com ([209.85.214.174]:36150 "EHLO mail-ob0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933020AbcCKBjy (ORCPT ); Thu, 10 Mar 2016 20:39:54 -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> From: Andy Lutomirski Date: Thu, 10 Mar 2016 17:39:33 -0800 Message-ID: Subject: Re: Got FPU related warning on Intel Quark during boot To: Borislav Petkov Cc: Andy Shevchenko , Ingo Molnar , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , 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: 2405 Lines: 81 On Thu, Mar 10, 2016 at 6:59 AM, 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); > + > } > This looks wrong, too: /* * Once per bootup FPU initialization sequences that will run on most x86 CPUs: */ static void __init fpu__init_system_generic(void) { /* * Set up the legacy init FPU context. (xstate init might overwrite this * with a more modern format, if the CPU supports it.) */ fpstate_init_fxstate(&init_fpstate.fxsave); <-- wrong format on pre-FXSR CPUs fpu__init_system_mxcsr(); }