From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754001AbcGTSDH (ORCPT ); Wed, 20 Jul 2016 14:03:07 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35667 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753060AbcGTSDC (ORCPT ); Wed, 20 Jul 2016 14:03:02 -0400 Date: Wed, 20 Jul 2016 20:02:56 +0200 From: Ingo Molnar To: Dave Hansen Cc: linux-kernel@vger.kernel.org, x86@kernel.org, dave.hansen@linux.intel.com Subject: Re: [PATCH] x86, fpu: do not BUG_ON() in early FPU code Message-ID: <20160720180256.GA14435@gmail.com> References: <20160720162328.A07B4C4B@viggo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160720162328.A07B4C4B@viggo.jf.intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Dave Hansen wrote: > > From: Dave Hansen > > I don't think it is really possible to have a system where CPUID > enumerates support for XSAVE but that it does not have FP/SSE > (they are "legacy" features and always present). > > But, I did manage to hit this case in qemu when I enabled its > somewhat shaky XSAVE support. The bummer is that the FPU is set > up before we parse the command-line or have *any* console support > including earlyprintk. > > So a BUG() here is worthless. All it does it guarantee that > if/when we hit this case we have an empty console. So, remove > the BUG() and try to limp along by disabling XSAVE and trying to > continue. > > Signed-off-by: Dave Hansen > --- > > b/arch/x86/kernel/fpu/xstate.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff -puN arch/x86/kernel/fpu/xstate.c~x86-fpu-do-not-BUG_ON-early arch/x86/kernel/fpu/xstate.c > --- a/arch/x86/kernel/fpu/xstate.c~x86-fpu-do-not-BUG_ON-early 2016-07-20 09:03:07.347941392 -0700 > +++ b/arch/x86/kernel/fpu/xstate.c 2016-07-20 09:17:15.001309137 -0700 > @@ -715,7 +715,8 @@ void __init fpu__init_system_xstate(void > > if ((xfeatures_mask & XFEATURE_MASK_FPSSE) != XFEATURE_MASK_FPSSE) { > pr_err("x86/fpu: FP/SSE not present amongst the CPU's xstate features: 0x%llx.\n", xfeatures_mask); > - BUG(); > + fpu__init_disable_system_xstate(); > + return; Ok, but please put a comment there explaining why we are not stopping the system. Thanks, Ingo