public: add and enable XENFEAT_ARM_SMCCC_supported feature

This feature indicates that hypervisor is compatible with ARM
SMC calling convention. Previously hypervisor would inject an
undefined instruction exception if an invalid SMC function were
called or would crash a domain if an invalid HVC function
were invoked.
XENFEAT_ARM_SMCCC_supported feature means that it safe to invoke
SMC/HVC calls that are compatible with SMC calling convention.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/common/kernel.c

@@ -394,6 +394,9 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
                     (1U << XENFEAT_auto_translated_physmap);
             if ( is_hardware_domain(d) )
                 fi.submap |= 1U << XENFEAT_dom0;
+#ifdef CONFIG_ARM
+            fi.submap |= (1U << XENFEAT_ARM_SMCCC_supported);
+#endif
 #ifdef CONFIG_X86
             switch ( d->guest_type )
             {

xen/include/public/features.h

@@ -102,6 +102,9 @@
 /* Guest can use XENMEMF_vnode to specify virtual node for memory op. */
 #define XENFEAT_memory_op_vnode_supported 13
 
+/* arm: Hypervisor supports ARM SMC calling convention. */
+#define XENFEAT_ARM_SMCCC_supported       14
+
 #define XENFEAT_NR_SUBMAPS 1
 
 #endif /* __XEN_PUBLIC_FEATURES_H__ */