linux-kernel - [PATCH v2 3/6] x86/cpu: Re-apply forced caps every time cpu caps are re-read

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Message-Id: <c817eb373d2c67c2c81413a70fc9b845fa34a37e.1484705016.git.luto@kernel.org>
Date:   Wed, 18 Jan 2017 11:15:39 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     X86 ML <x86@...nel.org>
Cc:     One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        Borislav Petkov <bp@...en8.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Matthew Whitehead <tedheadster@...il.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2 3/6] x86/cpu: Re-apply forced caps every time cpu caps are re-read

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 <luto@...nel.org>
---
 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 337eac606f39..8efe6e77f91d 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -757,6 +757,13 @@ 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);
 }
 
 static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
-- 
2.9.3