linux-kernel - [PATCH v2] x86/microcode/intel: replace sync_core() with native_cpuid

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Message-Id: <20200421085344.1804-1-evalds.iodzevics@gmail.com>
Date:   Tue, 21 Apr 2020 11:53:44 +0300
From:   Evalds Iodzevics <evalds.iodzevics@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     gregkh@...uxfoundation.org, tglx@...utronix.de,
        ben@...adent.org.uk, Evalds Iodzevics <evalds.iodzevics@...il.com>
Subject: [PATCH v2] x86/microcode/intel: replace sync_core() with native_cpuid_reg(eax)

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>
---
 arch/x86/include/asm/microcode_intel.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/microcode_intel.h b/arch/x86/include/asm/microcode_intel.h
index 90343ba50485..92ce9c8a508b 100644
--- a/arch/x86/include/asm/microcode_intel.h
+++ b/arch/x86/include/asm/microcode_intel.h
@@ -60,7 +60,7 @@ static inline u32 intel_get_microcode_revision(void)
 	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);
-- 
2.17.4