x86/microcode/amd: Extract current patch level read to a function

Pave the way for checking the current patch level of the
microcode in a core. We want to be able to do stuff depending on
the patch level - in this case decide whether to update or not.
But that will be added in a later patch.

Drop unused local var uci assignment, while at it.

Integrate a fix for 32-bit and CONFIG_PARAVIRT from Takashi Iwai:

 Use native_rdmsr() in check_current_patch_level() because with
 CONFIG_PARAVIRT enabled and on 32-bit, where we run before
 paging has been enabled, we cannot deref pv_info yet. Or we
 could, but we'd need to access its physical address. This way of
 fixing it is simpler. See:

   https://bugzilla.suse.com/show_bug.cgi?id=943179 for the background.

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Takashi Iwai <tiwai@suse.com>:
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/1444641762-9437-6-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/microcode/amd.c

@@ -177,6 +177,25 @@ static unsigned int verify_patch_size(u8 family, u32 patch_size,
 	return patch_size;
 }
 
+/*
+ * Check the current patch level on this CPU.
+ *
+ * @rev: Use it to return the patch level. It is set to 0 in the case of
+ * error.
+ *
+ * Returns:
+ *  - true: if update should stop
+ *  - false: otherwise
+ */
+bool check_current_patch_level(u32 *rev)
+{
+	u32 dummy;
+
+	native_rdmsr(MSR_AMD64_PATCH_LEVEL, *rev, dummy);
+
+	return false;
+}
+
 int __apply_microcode_amd(struct microcode_amd *mc_amd)
 {
 	u32 rev, dummy;
@@ -197,7 +216,7 @@ int apply_microcode_amd(int cpu)
 	struct microcode_amd *mc_amd;
 	struct ucode_cpu_info *uci;
 	struct ucode_patch *p;
-	u32 rev, dummy;
+	u32 rev;
 
 	BUG_ON(raw_smp_processor_id() != cpu);
 
@@ -210,7 +229,8 @@ int apply_microcode_amd(int cpu)
 	mc_amd  = p->data;
 	uci->mc = p->data;
 
-	rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
+	if (check_current_patch_level(&rev))
+		return -1;
 
 	/* need to apply patch? */
 	if (rev >= mc_amd->hdr.patch_id) {