KVM paravirt: Add async PF initialization to PV guest.

Enable async PF in a guest if async PF capability is discovered.

Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 8b61c93..369580d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1707,6 +1707,9 @@
 
 	no-kvmclock	[X86,KVM] Disable paravirtualized KVM clock driver
 
+	no-kvmapf	[X86,KVM] Disable paravirtualized asynchronous page
+			fault handling.
+
 	nolapic		[X86-32,APIC] Do not enable or use the local APIC.
 
 	nolapic_timer	[X86-32,APIC] Do not use the local APIC timer.