[PATCH] x86/HVM: expose VM assist hypercall

[Jan Beulich <jbeulich@xxxxxxxx>]

In preparation for the addition of VMASST_TYPE_runstate_update_flag
commit 72c538cca957 ("arm: add support for vm_assist hypercall") enabled
the hypercall for Arm. I consider it not logical that it then isn't also
exposed to x86 HVM guests (with the same single feature permitted to be
enabled as Arm has); Linux actually tries to use it afaict.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/hypercall.c
+++ b/xen/arch/x86/hvm/hypercall.c
@@ -78,6 +78,11 @@ static long hvm_grant_table_op(
 }
 #endif
 
+static long hvm_vm_assist(unsigned int cmd, unsigned int type)
+{
+    return vm_assist(current->domain, cmd, type, HVM_VM_ASSIST_VALID);
+}
+
 static long hvm_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
 {
     const struct vcpu *curr = current;
@@ -128,6 +133,7 @@ static const hypercall_table_t hvm_hyper
 #ifdef CONFIG_GRANT_TABLE
     HVM_CALL(grant_table_op),
 #endif
+    HVM_CALL(vm_assist),
     COMPAT_CALL(vcpu_op),
     HVM_CALL(physdev_op),
     COMPAT_CALL(xen_version),
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -319,6 +319,7 @@ extern unsigned long xen_phys_start;
 #define VM_ASSIST_VALID          NATIVE_VM_ASSIST_VALID
 #define COMPAT_VM_ASSIST_VALID   (NATIVE_VM_ASSIST_VALID & \
                                   ((1UL << COMPAT_BITS_PER_LONG) - 1))
+#define HVM_VM_ASSIST_VALID      (1UL << VMASST_TYPE_runstate_update_flag)
 
 #define ELFSIZE 64