x86, MCE: Drain mcelog buffer

Add a function which drains whatever MCEs were logged in already during
boot and before the decoder chains were registered.
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>

arch/x86/kernel/cpu/mcheck/mce.c

@@ -189,9 +189,48 @@ void mce_log(struct mce *mce)
 	set_bit(0, &mce_need_notify);
 }
 
+static void drain_mcelog_buffer(void)
+{
+	unsigned int next, i, prev = 0;
+
+	next = rcu_dereference_check_mce(mcelog.next);
+
+	do {
+		struct mce *m;
+
+		/* drain what was logged during boot */
+		for (i = prev; i < next; i++) {
+			unsigned long start = jiffies;
+			unsigned retries = 1;
+
+			m = &mcelog.entry[i];
+
+			while (!m->finished) {
+				if (time_after_eq(jiffies, start + 2*retries))
+					retries++;
+
+				cpu_relax();
+
+				if (!m->finished && retries >= 4) {
+					pr_err("MCE: skipping error being logged currently!\n");
+					break;
+				}
+			}
+			smp_rmb();
+			atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, m);
+		}
+
+		memset(mcelog.entry + prev, 0, (next - prev) * sizeof(*m));
+		prev = next;
+		next = cmpxchg(&mcelog.next, prev, 0);
+	} while (next != prev);
+}
+
+
 void mce_register_decode_chain(struct notifier_block *nb)
 {
 	atomic_notifier_chain_register(&x86_mce_decoder_chain, nb);
+	drain_mcelog_buffer();
 }
 EXPORT_SYMBOL_GPL(mce_register_decode_chain);