Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753255AbcCJPpd (ORCPT ); Thu, 10 Mar 2016 10:45:33 -0500 Received: from mail-wm0-f52.google.com ([74.125.82.52]:33138 "EHLO mail-wm0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752137AbcCJPpY (ORCPT ); Thu, 10 Mar 2016 10:45:24 -0500 Message-ID: <1457624721.5784.0.camel@nexus-software.ie> Subject: Re: Got FPU related warning on Intel Quark during boot From: "Bryan O'Donoghue" To: Andy Shevchenko , 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" Date: Thu, 10 Mar 2016 15:45:21 +0000 In-Reply-To: References: <20160310111935.GB13102@gmail.com> <20160310125610.GA26708@pd.tnic> <20160310145940.GB26708@pd.tnic> Content-Type: multipart/mixed; boundary="=-mZoOaG3rohYx38N8hV2r" X-Mailer: Evolution 3.16.5-1ubuntu3.1 Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4203 Lines: 141 --=-mZoOaG3rohYx38N8hV2r Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit On Thu, 2016-03-10 at 17:22 +0200, Andy Shevchenko wrote: > 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 > > > } > > > > /* > > > It works but user-space FPU is broken; something's wrong with the initial state of the FPU regs - it looks as though they aren't being properly initialized and FPU context in the signal handler is wrong too. Linux 3.8.7: /root@galileo:~# ./fpu f is 10.000000 g is 10.100000 Double value is 0.000000 Double value is 0.100000 Double value is 0.200000 ^Chandler value of variable is 0.300000 Double value is 0.300000 Double value is 0.400000 Linux-next + Boris' fix: root@galileo:~# ./fpu f is -nan g is -nan Double value is 0.000000 Double value is 0.100000 Double value is 0.200000^C handler value of variable is -nan Double value is 0.300000 Double value is 0.400000^Z[1]+ Stopped root@galileo:~# uname -aLinux galileo 4.5.0-rc7-next-20160310+ #185 Thu Mar 10 15:11:10 GMT 2016 i586 GNU/Linux --=-mZoOaG3rohYx38N8hV2r Content-Disposition: attachment; filename="fpu.c" Content-Type: text/x-csrc; name="fpu.c"; charset="UTF-8" Content-Transfer-Encoding: base64 I2luY2x1ZGUgPHN0ZGlvLmg+CiNpbmNsdWRlIDxzaWduYWwuaD4KI2luY2x1ZGUgPHN0cmluZy5o PgoKZmxvYXQgYSA9IDA7Cgp2b2lkIGhhbmRsZXIoaW50IHNpZ251bSwgc2lnaW5mb190ICppbmZv LCB2b2lkICpwdHIpCnsKCXByaW50ZigiJXMgdmFsdWUgb2YgdmFyaWFibGUgaXMgJWZcbiIsIF9f ZnVuY19fLCBhKTsKfQoKaW50IG1haW4oaW50IGFyZ2MsIGNoYXIgKmFyZ3ZbXSkKewoJc3RydWN0 IHNpZ2FjdGlvbiBzaWc7CglmbG9hdCBmID0gMTAsIGcgPSAxMC4xZjsKCgltZW1zZXQoJnNpZywg MHgwMCwgc2l6ZW9mKHNpZykpOwoJc2lnLnNhX3NpZ2FjdGlvbiA9IGhhbmRsZXI7CglzaWcuc2Ff ZmxhZ3MgPSBTQV9TSUdJTkZPOwoJc2lnYWN0aW9uKFNJR1RFUk0sICZzaWcsIE5VTEwpOwoJc2ln YWN0aW9uKFNJR0lOVCwgJnNpZywgTlVMTCk7CgoJcHJpbnRmKCJmIGlzICVmIGcgaXMgJWZcbiIs IGYsIGcpOwoJd2hpbGUoMSkgewoJCXNsZWVwKDEpOwoJCXByaW50ZigiRG91YmxlIHZhbHVlIGlz ICVmXG4iLCBhKTsKCQlhICs9IDAuMWY7Cgl9CglyZXR1cm4gMDsKfQoK --=-mZoOaG3rohYx38N8hV2r--