x86/idtentry: Provide IDTENTRY_XEN for XEN/PV

XEN/PV has special wrappers for NMI and DB exceptions. They redirect these
exceptions through regular IDTENTRY points. Provide the necessary IDTENTRY
macros to make this work

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200505135314.518622698@linutronix.de

arch/x86/include/asm/idtentry.h

@@ -168,6 +168,18 @@ __visible noinstr void func(struct pt_regs *regs)
 #define DECLARE_IDTENTRY_DEBUG		DECLARE_IDTENTRY_IST
 #define DEFINE_IDTENTRY_DEBUG		DEFINE_IDTENTRY_IST
 
+/**
+ * DECLARE_IDTENTRY_XEN - Declare functions for XEN redirect IDT entry points
+ * @vector:	Vector number (ignored for C)
+ * @func:	Function name of the entry point
+ *
+ * Used for xennmi and xendebug redirections. No DEFINE as this is all ASM
+ * indirection magic.
+ */
+#define DECLARE_IDTENTRY_XEN(vector, func)				\
+	asmlinkage void xen_asm_exc_xen##func(void);			\
+	asmlinkage void asm_exc_xen##func(void)
+
 #else /* !__ASSEMBLY__ */
 
 /*
@@ -203,6 +215,10 @@ __visible noinstr void func(struct pt_regs *regs)
 /* No ASM code emitted for NMI */
 #define DECLARE_IDTENTRY_NMI(vector, func)
 
+/* XEN NMI and DB wrapper */
+#define DECLARE_IDTENTRY_XEN(vector, func)				\
+	idtentry vector asm_exc_xen##func exc_##func has_error_code=0 sane=1
+
 #endif /* __ASSEMBLY__ */
 
 /*