x86/apic: Implement single target IPI function for x2apic_cluster

[ tglx: Split it out from the patch which provides the new callback ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Travis <travis@sgi.com>
Cc: Daniel J Blueman <daniel@numascale.com>
Link: http://lkml.kernel.org/r/20151104220848.817975597@linutronix.deSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/apic/x2apic_cluster.c

@@ -23,6 +23,14 @@ static inline u32 x2apic_cluster(int cpu)
 	return per_cpu(x86_cpu_to_logical_apicid, cpu) >> 16;
 }
 
+static void x2apic_send_IPI(int cpu, int vector)
+{
+	u32 dest = per_cpu(x86_cpu_to_logical_apicid, cpu);
+
+	x2apic_wrmsr_fence();
+	__x2apic_send_IPI_dest(dest, vector, APIC_DEST_LOGICAL);
+}
+
 static void
 __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest)
 {
@@ -266,6 +274,7 @@ static struct apic apic_x2apic_cluster = {
 
 	.cpu_mask_to_apicid_and		= x2apic_cpu_mask_to_apicid_and,
 
+	.send_IPI			= x2apic_send_IPI,
 	.send_IPI_mask			= x2apic_send_IPI_mask,
 	.send_IPI_mask_allbutself	= x2apic_send_IPI_mask_allbutself,
 	.send_IPI_allbutself		= x2apic_send_IPI_allbutself,