[PATCH 2/2] x86/microcode: Do the family check first

[Rolf Neugebauer]

From: Borislav Petkov <bp@xxxxxxx>

commit 1f161f67a272cc4f29f27934dd3f74cb657eb5c4 upstream with adjustments.

On CPUs like AMD's Geode, for example, we shouldn't even try to load
microcode because they do not support the modern microcode loading
interface.

However, we do the family check *after* the other checks whether the
loader has been disabled on the command line or whether we're running in
a guest.

So move the family checks first in order to exit early if we're being
loaded on an unsupported family.

Reported-and-tested-by: Sven Glodowski <glodi1@xxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.11..
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://bugzilla.suse.com/show_bug.cgi?id=1061396
Link: http://lkml.kernel.org/r/20171012112316.977-1-bp@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.4.x
Signed-off-by: Rolf Neugebauer <rolf.neugebauer@xxxxxxxxxx>
---
 arch/x86/kernel/cpu/microcode/core.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 1b3e0aa4c511..ce5f8a2e7ae6 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -94,9 +94,6 @@ static bool __init check_loader_disabled_bsp(void)
 	bool *res = &dis_ucode_ldr;
 #endif
 
-	if (!have_cpuid_p())
-		return *res;
-
 	a = 1;
 	c = 0;
 	native_cpuid(&a, &b, &c, &d);
@@ -138,8 +135,9 @@ void __init load_ucode_bsp(void)
 {
 	int vendor;
 	unsigned int family;
+	bool intel = true;
 
-	if (check_loader_disabled_bsp())
+	if (!have_cpuid_p())
 		return;
 
 	vendor = x86_vendor();
@@ -147,16 +145,27 @@ void __init load_ucode_bsp(void)
 
 	switch (vendor) {
 	case X86_VENDOR_INTEL:
-		if (family >= 6)
-			load_ucode_intel_bsp();
+		if (family < 6)
+			return;
 		break;
+
 	case X86_VENDOR_AMD:
-		if (family >= 0x10)
-			load_ucode_amd_bsp(family);
+		if (family < 0x10)
+			return;
+		intel = false;
 		break;
+
 	default:
-		break;
+		return;
 	}
+
+	if (check_loader_disabled_bsp())
+		return;
+
+	if (intel)
+		load_ucode_intel_bsp();
+	else
+		load_ucode_amd_bsp(family);
 }
 
 static bool check_loader_disabled_ap(void)
-- 
2.16.0