linux-kernel - [PATCH 4.9 124/125] x86/microcode/intel: replace sync_core() with native_cpuid

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Message-Id: <20200422095052.422785226@linuxfoundation.org>
Date:   Wed, 22 Apr 2020 11:57:21 +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,
        Evalds Iodzevics <evalds.iodzevics@...il.com>
Subject: [PATCH 4.9 124/125] x86/microcode/intel: replace sync_core() with native_cpuid_reg(eax)

From: Evalds Iodzevics <evalds.iodzevics@...il.com>

On Intel it is required to do CPUID(1) before reading the microcode
revision MSR. Current code in 4.4 an 4.9 relies on sync_core() to call
CPUID, unfortunately on 32 bit machines code inside sync_core() always
jumps past CPUID instruction as it depends on data structure boot_cpu_data
witch are not populated correctly so early in boot sequence.

It depends on:
commit 5dedade6dfa2 ("x86/CPU: Add native CPUID variants returning a single
datum")

This patch is for 4.4 but also should apply to 4.9

Signed-off-by: Evalds Iodzevics <evalds.iodzevics@...il.com>
Cc: stable@...r.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/include/asm/microcode_intel.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/microcode_intel.h
+++ b/arch/x86/include/asm/microcode_intel.h
@@ -59,7 +59,7 @@ static inline u32 intel_get_microcode_re
 	native_wrmsrl(MSR_IA32_UCODE_REV, 0);
 
 	/* As documented in the SDM: Do a CPUID 1 here */
-	sync_core();
+	native_cpuid_eax(1);
 
 	/* get the current revision from MSR 0x8B */
 	native_rdmsr(MSR_IA32_UCODE_REV, dummy, rev);