[v2 1/3] x86/microcode/intel: Check microcode revision before updating sibling threads

[Ashok Raj]

After updating microcode on one of the threads in the core, the
thread sibling automatically gets the update since the microcode
resources are shared. Check the ucode revision on the CPU before
performing a ucode update.

Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
Cc: X86 ML <x86@xxxxxxxxxx>
Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Andi Kleen <andi.kleen@xxxxxxxxx>
Cc: Boris Petkov <bp@xxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Arjan Van De Ven <arjan.van.de.ven@xxxxxxxxx>

Updates:
v2: Address Boris's to cleanup apply_microcode_intel
v3: Fixups per Ingo: Spell Checks
---
 arch/x86/kernel/cpu/microcode/intel.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 09b95a7..137c9f5 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -589,6 +589,18 @@ static int apply_microcode_early(struct ucode_cpu_info *uci, bool early)
 	if (!mc)
 		return 0;
 
+	rev = intel_get_microcode_revision();
+
+	/*
+	 * Its possible the microcode got updated
+	 * because its sibling update was done earlier.
+	 * Skip the update in that case.
+	 */
+	if (rev >= mc->hdr.rev) {
+		uci->cpu_sig.rev = rev;
+		return UCODE_OK;
+	}
+
 	/* write microcode via MSR 0x79 */
 	native_wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);
 
@@ -776,7 +788,7 @@ static enum ucode_state apply_microcode_intel(int cpu)
 {
 	struct microcode_intel *mc;
 	struct ucode_cpu_info *uci;
-	struct cpuinfo_x86 *c;
+	struct cpuinfo_x86 *c = &cpu_data(cpu);
 	static int prev_rev;
 	u32 rev;
 
@@ -793,6 +805,18 @@ static enum ucode_state apply_microcode_intel(int cpu)
 			return UCODE_NFOUND;
 	}
 
+	rev = intel_get_microcode_revision();
+	/*
+	 * Its possible the microcode got updated
+	 * because its sibling update was done earlier.
+	 * Skip the update in that case.
+	 */
+	if (rev >= mc->hdr.rev) {
+		uci->cpu_sig.rev = rev;
+		c->microcode = rev;
+		return UCODE_OK;
+	}
+
 	/* write microcode via MSR 0x79 */
 	wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);
 
@@ -813,8 +837,6 @@ static enum ucode_state apply_microcode_intel(int cpu)
 		prev_rev = rev;
 	}
 
-	c = &cpu_data(cpu);
-
 	uci->cpu_sig.rev = rev;
 	c->microcode = rev;
 
-- 
2.7.4