linux-kernel - [tip:x86/cpu] x86/CPU: Change query logic so CPUID is enabled before testing

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Message-ID: <tip-2893cc8ff892fa74972d8dc0e1d0dc65116daaa3@git.kernel.org>
Date:   Sat, 22 Sep 2018 02:58:27 -0700
From:   tip-bot for Matthew Whitehead <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     konrad.wilk@...cle.com, hpa@...or.com, tedheadster@...il.com,
        bp@...e.de, linux-kernel@...r.kernel.org, mingo@...nel.org,
        luto@...capital.net, dwmw@...zon.co.uk, peterz@...radead.org,
        tglx@...utronix.de
Subject: [tip:x86/cpu] x86/CPU: Change query logic so CPUID is enabled
 before testing

Commit-ID:  2893cc8ff892fa74972d8dc0e1d0dc65116daaa3
Gitweb:     https://git.kernel.org/tip/2893cc8ff892fa74972d8dc0e1d0dc65116daaa3
Author:     Matthew Whitehead <tedheadster@...il.com>
AuthorDate: Fri, 21 Sep 2018 17:20:41 -0400
Committer:  Borislav Petkov <bp@...e.de>
CommitDate: Sat, 22 Sep 2018 11:47:39 +0200

x86/CPU: Change query logic so CPUID is enabled before testing

Presently we check first if CPUID is enabled. If it is not already
enabled, then we next call identify_cpu_without_cpuid() and clear
X86_FEATURE_CPUID.

Unfortunately, identify_cpu_without_cpuid() is the function where CPUID
becomes _enabled_ on Cyrix 6x86/6x86L CPUs.

Reverse the calling sequence so that CPUID is first enabled, and then
check a second time to see if the feature has now been activated.

[ bp: Massage commit message and remove trailing whitespace. ]

Suggested-by: Andy Lutomirski <luto@...capital.net>
Signed-off-by: Matthew Whitehead <tedheadster@...il.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Andy Lutomirski <luto@...capital.net>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20180921212041.13096-3-tedheadster@gmail.com
---
 arch/x86/kernel/cpu/common.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 44c4ef3d989b..658c85d16a9b 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1076,6 +1076,9 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 	memset(&c->x86_capability, 0, sizeof c->x86_capability);
 	c->extended_cpuid_level = 0;
 
+	if (!have_cpuid_p())
+		identify_cpu_without_cpuid(c);
+
 	/* cyrix could have cpuid enabled via c_identify()*/
 	if (have_cpuid_p()) {
 		cpu_detect(c);
@@ -1093,7 +1096,6 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 		if (this_cpu->c_bsp_init)
 			this_cpu->c_bsp_init(c);
 	} else {
-		identify_cpu_without_cpuid(c);
 		setup_clear_cpu_cap(X86_FEATURE_CPUID);
 	}