linux-kernel - [PATCH 4.9 18/52] x86/cpu: Re-apply forced caps every time CPU caps are re-read

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Date:   Tue, 10 Jul 2018 20:24:46 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Whitehead <tedheadster@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.9 18/52] x86/cpu: Re-apply forced caps every time CPU caps are re-read

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@...nel.org>

commit 60d3450167433f2d099ce2869dc52dd9e7dc9b29 upstream.

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
features 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 <luto@...nel.org>
Reviewed-by: Borislav Petkov <bp@...e.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Matthew Whitehead <tedheadster@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@...el.com>
Link: http://lkml.kernel.org/r/c817eb373d2c67c2c81413a70fc9b845fa34a37e.1484705016.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/cpu/common.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -848,6 +848,13 @@ void get_cpu_cap(struct cpuinfo_x86 *c)

 	init_scattered_cpuid_features(c);
 	init_speculation_control(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);
 }

 static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)