ioreq: do not build arch_vcpu_ioreq_completion() for non-VMX configurations

VIO_realmode_completion is specific to vmx realmode and thus the function
arch_vcpu_ioreq_completion() has actual handling work only in VMX-enabled build,
as for the rest x86 and ARM build configurations it is basically a stub.

Here a separate configuration option ARCH_VCPU_IOREQ_COMPLETION introduced that
tells whether the platform we're building for requires any specific ioreq
completion handling. As of now only VMX has such requirement, so the option is
selected by INTEL_VMX, for other configurations a generic default stub is
provided (it is ARM's version of arch_vcpu_ioreq_completion() moved to common
header).

Signed-off-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@epam.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/Kconfig

@@ -95,4 +95,11 @@ config LTO
 config ARCH_SUPPORTS_INT128
 	bool
 
+#
+# For platforms that require specific handling of per-vCPU ioreq completion
+# events
+#
+config ARCH_VCPU_IOREQ_COMPLETION
+	bool
+
 source "Kconfig.debug"

xen/arch/arm/ioreq.c

@@ -135,12 +135,6 @@ bool arch_ioreq_complete_mmio(void)
     return false;
 }
 
-bool arch_vcpu_ioreq_completion(enum vio_completion completion)
-{
-    ASSERT_UNREACHABLE();
-    return true;
-}
-
 /*
  * The "legacy" mechanism of mapping magic pages for the IOREQ servers
  * is x86 specific, so the following hooks don't need to be implemented on Arm:

xen/arch/x86/Kconfig

@@ -127,6 +127,7 @@ config AMD_SVM
 
 config INTEL_VMX
 	def_bool HVM
+	select ARCH_VCPU_IOREQ_COMPLETION
 
 config XEN_SHSTK
 	bool "Supervisor Shadow Stacks"

xen/arch/x86/hvm/ioreq.c

@@ -29,6 +29,7 @@ bool arch_ioreq_complete_mmio(void)
     return handle_mmio();
 }
 
+#ifdef CONFIG_VCPU_ARCH_IOREQ_COMPLETION
 bool arch_vcpu_ioreq_completion(enum vio_completion completion)
 {
     switch ( completion )
@@ -51,6 +52,7 @@ bool arch_vcpu_ioreq_completion(enum vio_completion completion)
 
     return true;
 }
+#endif
 
 static gfn_t hvm_alloc_legacy_ioreq_gfn(struct ioreq_server *s)
 {

xen/include/xen/ioreq.h

@@ -111,7 +111,17 @@ void ioreq_domain_init(struct domain *d);
 int ioreq_server_dm_op(struct xen_dm_op *op, struct domain *d, bool *const_op);
 
 bool arch_ioreq_complete_mmio(void);
+
+#ifdef CONFIG_VCPU_ARCH_IOREQ_COMPLETION
 bool arch_vcpu_ioreq_completion(enum vio_completion completion);
+#else
+static inline bool arch_vcpu_ioreq_completion(enum vio_completion completion)
+{
+    ASSERT_UNREACHABLE();
+    return true;
+}
+#endif
+
 int arch_ioreq_server_map_pages(struct ioreq_server *s);
 void arch_ioreq_server_unmap_pages(struct ioreq_server *s);
 void arch_ioreq_server_enable(struct ioreq_server *s);