[PATCH] KVM: X86: Use IPI shorthands in kvm guest when support

[Wanpeng Li <kernellwp@gmail.com>]

From: Wanpeng Li <wanpengli@tencent.com>

IPI shorthand is supported now by linux apic/x2apic driver, switch to 
IPI shorthand for all excluding self and all including self destination 
shorthand in kvm guest, to avoid splitting the target mask into serveral 
PV IPI hypercalls.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Nadav Amit <namit@vmware.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
Note: rebase against tip tree's x86/apic branch

 arch/x86/kernel/kvm.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index b7f34fe..87b73b8 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -34,7 +34,9 @@
 #include <asm/hypervisor.h>
 #include <asm/tlb.h>
 
+static struct apic orig_apic;
 static int kvmapf = 1;
+DECLARE_STATIC_KEY_FALSE(apic_use_ipi_shorthand);
 
 static int __init parse_no_kvmapf(char *arg)
 {
@@ -507,12 +509,18 @@ static void kvm_send_ipi_mask_allbutself(const struct cpumask *mask, int vector)
 
 static void kvm_send_ipi_allbutself(int vector)
 {
-	kvm_send_ipi_mask_allbutself(cpu_online_mask, vector);
+	if (static_branch_likely(&apic_use_ipi_shorthand))
+		orig_apic.send_IPI_allbutself(vector);
+	else
+		kvm_send_ipi_mask_allbutself(cpu_online_mask, vector);
 }
 
 static void kvm_send_ipi_all(int vector)
 {
-	__send_ipi_mask(cpu_online_mask, vector);
+	if (static_branch_likely(&apic_use_ipi_shorthand))
+		orig_apic.send_IPI_allbutself(vector);
+	else
+		__send_ipi_mask(cpu_online_mask, vector);
 }
 
 /*
@@ -520,6 +528,8 @@ static void kvm_send_ipi_all(int vector)
  */
 static void kvm_setup_pv_ipi(void)
 {
+	orig_apic = *apic;
+
 	apic->send_IPI_mask = kvm_send_ipi_mask;
 	apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself;
 	apic->send_IPI_allbutself = kvm_send_ipi_allbutself;
-- 
2.7.4