[PATCH RFC 7/7] x86/microcode/intel: Enable staging when available

[Chang S. Bae]

With the staging code being ready, check the relevant MSRs and set the
feature chicken bit to allow staging to be invoked from the core
microcode update process.

Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
---
 arch/x86/kernel/cpu/microcode/intel.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 03c4b0e7e97c..8f2476fbe8f2 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -688,6 +688,18 @@ static __init void calc_llc_size_per_core(struct cpuinfo_x86 *c)
 	llc_size_per_core = (unsigned int)llc_size;
 }
 
+static __init bool staging_available(void)
+{
+	u64 val;
+
+	val = x86_read_arch_cap_msr();
+	if (!(val & ARCH_CAP_MCU_ENUM))
+		return false;
+
+	rdmsrl(MSR_IA32_MCU_ENUMERATION, val);
+	return !!(val & MCU_STAGING);
+}
+
 struct microcode_ops * __init init_intel_microcode(void)
 {
 	struct cpuinfo_x86 *c = &boot_cpu_data;
@@ -698,6 +710,11 @@ struct microcode_ops * __init init_intel_microcode(void)
 		return NULL;
 	}
 
+	if (staging_available()) {
+		pr_info("Staging is available.\n");
+		microcode_intel_ops.use_staging = true;
+	}
+
 	calc_llc_size_per_core(c);
 
 	return &microcode_intel_ops;
-- 
2.43.0