x86/xen: event channels delivery on HVM.

Set the callback to receive evtchns from Xen, using the
callback vector delivery mechanism.

The traditional way for receiving event channel notifications from Xen
is via the interrupts from the platform PCI device.
The callback vector is a newer alternative that allow us to receive
notifications on any vcpu and doesn't need any PCI support: we allocate
a vector exclusively to receive events, in the vector handler we don't
need to interact with the vlapic, therefore we avoid a VMEXIT.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 0697ff13983..490ae2bb18a 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1329,6 +1329,9 @@ ENTRY(xen_failsafe_callback)
         CFI_ENDPROC
 END(xen_failsafe_callback)
 
+apicinterrupt XEN_HVM_EVTCHN_CALLBACK \
+        xen_hvm_callback_vector xen_evtchn_do_upcall
+
 #endif /* CONFIG_XEN */
 
 /*