[PATCH 2/5] x86/microcode: Use native CPUID to tickle out microcode revision

[Borislav Petkov]

From: Borislav Petkov <bp@xxxxxxx>

Intel supplies the microcode revision value in MSR 0x8b
(IA32_BIOS_SIGN_ID) after CPUID(1) has been executed. Execute it each
time before reading that MSR.

It used to do sync_core() which did do CPUID but

  c198b121b1a1 ("x86/asm: Rewrite sync_core() to use IRET-to-self")

changed the sync_core() implementation so we better make the microcode
loading case explicit, as the SDM documents it.

Reported-and-tested-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/kernel/cpu/intel.c           |  2 +-
 arch/x86/kernel/cpu/microcode/intel.c | 26 +++-----------------------
 2 files changed, 4 insertions(+), 24 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index fcd484d2bb03..2d49aa949fa1 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -83,7 +83,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 
 		wrmsr(MSR_IA32_UCODE_REV, 0, 0);
 		/* Required by the SDM */
-		sync_core();
+		native_cpuid_eax(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 b624b54912e1..f79249fab389 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -368,26 +368,6 @@ scan_microcode(void *data, size_t size, struct ucode_cpu_info *uci, bool save)
 	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();
+	native_cpuid_eax(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();
+	native_cpuid_eax(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();
+	native_cpuid_eax(1);
 
 	/* get the current revision from MSR 0x8B */
 	rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
-- 
2.11.0