linux-kernel - [PATCH AUTOSEL 4.19 087/191] x86/CPU: Change query logic so CPUID is enabled before testing

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Date:   Sat,  9 Nov 2019 21:38:29 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Matthew Whitehead <tedheadster@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...e.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.19 087/191] x86/CPU: Change query logic so CPUID is enabled before testing

From: Matthew Whitehead <tedheadster@...il.com>

[ Upstream commit 2893cc8ff892fa74972d8dc0e1d0dc65116daaa3 ]

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
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 b33fdfa0ff49e..04622625f8e22 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1104,6 +1104,9 @@ 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);
@@ -1121,7 +1124,6 @@ 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);
 	}
 
-- 
2.20.1