Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752872AbcLFI5d (ORCPT ); Tue, 6 Dec 2016 03:57:33 -0500 Received: from mail.skyhub.de ([78.46.96.112]:52061 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751993AbcLFI5c (ORCPT ); Tue, 6 Dec 2016 03:57:32 -0500 Date: Tue, 6 Dec 2016 09:57:26 +0100 From: Borislav Petkov To: Andy Lutomirski , Thomas Gleixner Cc: x86@kernel.org, One Thousand Gnomes , "linux-kernel@vger.kernel.org" , Brian Gerst , Matthew Whitehead Subject: Re: [RFC PATCH 3/6] x86/cpu: Re-apply forced caps every time cpu caps are re-read Message-ID: <20161206085726.b6jaxmtjse5oa2od@pd.tnic> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20161014 (1.7.1) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1792 Lines: 50 On Mon, Dec 05, 2016 at 05:01:12PM -0800, Andy Lutomirski wrote: > Calling get_cpu_cap() will reset a bunch of CPU features. This will > cause the system to lose track of force-set and force-cleared > featueres in the words that are reset until the end of CPU > initialization. This can cause X86_FEATURE_FPU, for example, to > change back and forth during boot and potentially confuse CPU setup. > > To minimize the chance of confusion, re-apply forced caps every time > get_cpu_cap() is called. > > Signed-off-by: Andy Lutomirski > --- > arch/x86/kernel/cpu/common.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c > index 347ae0a19380..24e1e4004d42 100644 > --- a/arch/x86/kernel/cpu/common.c > +++ b/arch/x86/kernel/cpu/common.c > @@ -758,6 +758,13 @@ void get_cpu_cap(struct cpuinfo_x86 *c) > c->x86_capability[CPUID_8000_000A_EDX] = cpuid_edx(0x8000000a); > > init_scattered_cpuid_features(c); > + > + /* > + * Clear/Set all flags overridden by options, after probe. > + * This needs to happen each time we re-probe, which may happen > + * several times during CPU initialization. > + */ > + apply_forced_caps(c); I guess... Although I have to say all that early capabilities detection has grown a lot of cruft during the years and is nuts. And calling get_cpu_cap() multiple times is simply plain wrong. What we should do is read CPUID *once*, filter out caps and set our internal representation bits and be done with it. Stuff like setup_pku() which *sets* CPUID bits will then have to run *before* we do the detection and that's it. But I guess that's future work. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.