x86/xen: Support early interrupts in xen pv guests

Add early interrupt handlers activated by idt_setup_early_handler() to
the handlers supported by Xen pv guests. This will allow for early
WARN() calls not crashing the guest.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel@lists.xenproject.org
Cc: boris.ostrovsky@oracle.com
Link: https://lkml.kernel.org/r/20171124084221.30172-1-jgross@suse.com

arch/x86/xen/xen-asm_64.S

@@ -15,6 +15,7 @@
 
 #include <xen/interface/xen.h>
 
+#include <linux/init.h>
 #include <linux/linkage.h>
 
 .macro xen_pv_trap name
@@ -54,6 +55,19 @@ xen_pv_trap entry_INT80_compat
 #endif
 xen_pv_trap hypervisor_callback
 
+	__INIT
+ENTRY(xen_early_idt_handler_array)
+	i = 0
+	.rept NUM_EXCEPTION_VECTORS
+	pop %rcx
+	pop %r11
+	jmp early_idt_handler_array + i*EARLY_IDT_HANDLER_SIZE
+	i = i + 1
+	.fill xen_early_idt_handler_array + i*XEN_EARLY_IDT_HANDLER_SIZE - ., 1, 0xcc
+	.endr
+END(xen_early_idt_handler_array)
+	__FINIT
+
 hypercall_iret = hypercall_page + __HYPERVISOR_iret * 32
 /*
  * Xen64 iret frame: