powerpc: Rate-limit users spamming kernel log buffer

The facility unavailable exception can be triggered from userspace by
accessing PMU registers when EBB is not enabled.  This causes the
included pr_err() to run, hence spamming the kernel log buffer.

This avoids this by rate limiting these messages.
Signed-off-by: NMichael Neuling <mikey@neuling.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/traps.c

@@ -1379,8 +1379,9 @@ void facility_unavailable_exception(struct pt_regs *regs)
 	if (!arch_irq_disabled_regs(regs))
 		local_irq_enable();
 
-	pr_err("%sFacility '%s' unavailable, exception at 0x%lx, MSR=%lx\n",
-	       hv ? "Hypervisor " : "", facility, regs->nip, regs->msr);
+	pr_err_ratelimited(
+		"%sFacility '%s' unavailable, exception at 0x%lx, MSR=%lx\n",
+		hv ? "Hypervisor " : "", facility, regs->nip, regs->msr);
 
 	if (user_mode(regs)) {
 		_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);