x86: avoid wrong use of all-but-self IPI shorthand

With "nosmp" I did observe a flood of "APIC error on CPU0: 04(04), Send
accept error" log messages on an AMD system. And rightly so - nothing
excludes the use of the shorthand in send_IPI_mask() in this case. Set
"unaccounted_cpus" to "true" also when command line restrictions are the
cause.

Note that PV-shim mode is unaffected by this change, first and foremost
because "nosmp" and "maxcpus=" are ignored in this case.

Fixes: 5500d265a2 ("x86/smp: use APIC ALLBUT destination shorthand when possible")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 7621880de0
master date: 2021-12-10 10:26:52 +0100

xen/arch/x86/mpparse.c

@@ -85,9 +85,14 @@ void __init set_nr_cpu_ids(unsigned int max_cpus)
 	if (!park_offline_cpus)
 		tot_cpus = max_cpus;
 	nr_cpu_ids = min(tot_cpus, NR_CPUS + 0u);
-	if (park_offline_cpus && nr_cpu_ids < num_processors)
-		printk(XENLOG_WARNING "SMP: Cannot bring up %u further CPUs\n",
-		       num_processors - nr_cpu_ids);
+	if (nr_cpu_ids < num_processors)
+	{
+		unaccounted_cpus = true;
+		if (park_offline_cpus)
+			printk(XENLOG_WARNING
+			       "SMP: Cannot bring up %u further CPUs\n",
+			       num_processors - nr_cpu_ids);
+	}
 
 #ifndef nr_cpumask_bits
 	nr_cpumask_bits = ROUNDUP(nr_cpu_ids, BITS_PER_LONG);