linux-kernel - [PATCH] x86: Fix Intel microcode revision detection

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Date:   Wed, 28 Dec 2016 04:39:31 +0000
From:   Junichi Nomura <j-nomura@...jp.nec.com>
To:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "bp@...en8.de" <bp@...en8.de>
Subject: [PATCH] x86: Fix Intel microcode revision detection

early_init_intel() calls sync_core() before rdmsr(MSR_IA32_UCODE_REV),
assuming sync_core() is effectively CPUID(eax=1). However the assumption
no longer holds since commit c198b121b1a1 ("x86/asm: Rewrite sync_core()
to use IRET-to-self").

As a result, kernel fails to detect the revision of microcode, such as:
  microcode: sig=0x206a7, pf=0x2, revision=0x0

Conversion from sync_core() to native_cpuid() has already been done in
Intel microcode driver by commit 484d0e5c7943 ("x86/microcode/intel:
Replace sync_core() with native_cpuid()"). This patch just extends the
conversion for early_init_intel().

Fixes: c198b121b1a1 ("x86/asm: Rewrite sync_core() to use IRET-to-self")
Signed-off-by: Jun'ichi Nomura <j-nomura@...jp.nec.com>
Cc: Andy Lutomirski <luto@...capital.net>

diff --git a/arch/x86/include/asm/microcode_intel.h b/arch/x86/include/asm/microcode_intel.h
index 195becc..19cb4c4 100644
--- a/arch/x86/include/asm/microcode_intel.h
+++ b/arch/x86/include/asm/microcode_intel.h
@@ -66,4 +66,24 @@ static inline void show_ucode_info_early(void) {}
 static inline void reload_ucode_intel(void) {}
 #endif
 
+static inline void intel_microcode_cpuid_1(void)
+{
+	/*
+	 * According to the Intel SDM, Volume 3, 9.11.7:
+	 *
+	 *   CPUID returns a value in a model specific register in
+	 *   addition to its usual register return values. The
+	 *   semantics of CPUID cause it to deposit an update ID value
+	 *   in the 64-bit model-specific register at address 08BH
+	 *   (IA32_BIOS_SIGN_ID). If no update is present in the
+	 *   processor, the value in the MSR remains unmodified.
+	 *
+	 * Use native_cpuid -- this code runs very early and we don't
+	 * want to mess with paravirt.
+	 */
+	unsigned int eax = 1, ebx, ecx = 0, edx;
+
+	native_cpuid(&eax, &ebx, &ecx, &edx);
+}
+
 #endif /* _ASM_X86_MICROCODE_INTEL_H */
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index fcd484d..edc38a9 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -14,6 +14,7 @@
 #include <asm/bugs.h>
 #include <asm/cpu.h>
 #include <asm/intel-family.h>
+#include <asm/microcode_intel.h>
 
 #ifdef CONFIG_X86_64
 #include <linux/topology.h>
@@ -83,7 +84,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 
 		wrmsr(MSR_IA32_UCODE_REV, 0, 0);
 		/* Required by the SDM */
-		sync_core();
+		intel_microcode_cpuid_1();
 		rdmsr(MSR_IA32_UCODE_REV, lower_word, c->microcode);
 	}
 
diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index b624b54..546c6cf 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -368,26 +368,6 @@ static int microcode_sanity_check(void *mc, int print_err)
 	return patch;
 }
 
-static void cpuid_1(void)
-{
-	/*
-	 * According to the Intel SDM, Volume 3, 9.11.7:
-	 *
-	 *   CPUID returns a value in a model specific register in
-	 *   addition to its usual register return values. The
-	 *   semantics of CPUID cause it to deposit an update ID value
-	 *   in the 64-bit model-specific register at address 08BH
-	 *   (IA32_BIOS_SIGN_ID). If no update is present in the
-	 *   processor, the value in the MSR remains unmodified.
-	 *
-	 * Use native_cpuid -- this code runs very early and we don't
-	 * want to mess with paravirt.
-	 */
-	unsigned int eax = 1, ebx, ecx = 0, edx;
-
-	native_cpuid(&eax, &ebx, &ecx, &edx);
-}
-
 static int collect_cpu_info_early(struct ucode_cpu_info *uci)
 {
 	unsigned int val[2];
@@ -413,7 +393,7 @@ static int collect_cpu_info_early(struct ucode_cpu_info *uci)
 	native_wrmsrl(MSR_IA32_UCODE_REV, 0);
 
 	/* As documented in the SDM: Do a CPUID 1 here */
-	cpuid_1();
+	intel_microcode_cpuid_1();
 
 	/* get the current revision from MSR 0x8B */
 	native_rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
@@ -613,7 +593,7 @@ static int apply_microcode_early(struct ucode_cpu_info *uci, bool early)
 	native_wrmsrl(MSR_IA32_UCODE_REV, 0);
 
 	/* As documented in the SDM: Do a CPUID 1 here */
-	cpuid_1();
+	intel_microcode_cpuid_1();
 
 	/* get the current revision from MSR 0x8B */
 	native_rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
@@ -825,7 +805,7 @@ static int apply_microcode_intel(int cpu)
 	wrmsrl(MSR_IA32_UCODE_REV, 0);
 
 	/* As documented in the SDM: Do a CPUID 1 here */
-	cpuid_1();
+	intel_microcode_cpuid_1();
 
 	/* get the current revision from MSR 0x8B */
 	rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);