x86/microcode: Do the family check first

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@arcor.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org> # 4.11..
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://bugzilla.suse.com/show_bug.cgi?id=1061396
Link: http://lkml.kernel.org/r/20171012112316.977-1-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 18 insertions, 9 deletions

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 86e8f0b2537b..c4fa4a85d4cb 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -122,9 +122,6 @@ static bool __init check_loader_disabled_bsp(void)
         bool *res = &dis_ucode_ldr;
 #endif
 
-        if (!have_cpuid_p())
-                return *res;
-
         /*
          * CPUID(1).ECX[31]: reserved for hypervisor use. This is still not
          * completely accurate as xen pv guests don't see that CPUID bit set but
@@ -166,24 +163,36 @@ bool get_builtin_firmware(struct cpio_data *cd, const char *name)
 void __init load_ucode_bsp(void)
 {
         unsigned int cpuid_1_eax;
+        bool intel = true;
 
-        if (check_loader_disabled_bsp())
+        if (!have_cpuid_p())
                 return;
 
         cpuid_1_eax = native_cpuid_eax(1);
 
         switch (x86_cpuid_vendor()) {
         case X86_VENDOR_INTEL:
-                if (x86_family(cpuid_1_eax) >= 6)
-                        load_ucode_intel_bsp();
+                if (x86_family(cpuid_1_eax) < 6)
+                        return;
                 break;
+
         case X86_VENDOR_AMD:
-                if (x86_family(cpuid_1_eax) >= 0x10)
-                        load_ucode_amd_bsp(cpuid_1_eax);
+                if (x86_family(cpuid_1_eax) < 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(cpuid_1_eax);
 }
 
 static bool check_loader_disabled_ap(void)