hv: allocate synic pages for all present CPUs

commit 421b8f20 upstream.

It may happen that not all CPUs are online when we do hv_synic_alloc() and
in case more CPUs come online later we may try accessing these allocated
structures.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/hv/hv.c

@@ -264,7 +264,7 @@ int hv_synic_alloc(void)
 	size_t size = sizeof(struct tasklet_struct);
 	int cpu;
 
-	for_each_online_cpu(cpu) {
+	for_each_present_cpu(cpu) {
 		hv_context.event_dpc[cpu] = kmalloc(size, GFP_ATOMIC);
 		if (hv_context.event_dpc[cpu] == NULL) {
 			pr_err("Unable to allocate event dpc\n");
@@ -317,7 +317,7 @@ void hv_synic_free(void)
 {
 	int cpu;
 
-	for_each_online_cpu(cpu)
+	for_each_present_cpu(cpu)
 		hv_synic_free_cpu(cpu);
 }