xen: arm: document which hypercalls (and subops) are supported on ARM

There are many hypercalls which make no sense or which are not supported on ARM
systems but it's not all that obvious which ones we do support. So lets try and
document the hypercalls which are useful on ARM.

I'm not sure this is the best way to go about this, I'm open to other ideas.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>?

1 files changed, 64 insertions, 2 deletions

diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index cbd53a9eda..e9842b8d4f 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -27,8 +27,8 @@
 #ifndef __XEN_PUBLIC_ARCH_ARM_H__
 #define __XEN_PUBLIC_ARCH_ARM_H__
 
-/* hypercall calling convention
- * ----------------------------
+/*
+ * `incontents 50 arm_abi Hypercall Calling Convention
  *
  * A hypercall is issued using the ARM HVC instruction.
  *
@@ -60,6 +60,68 @@
  * hypercall arguments are always little endian.
  */
 
+/*
+ * `incontents 55 arm_hcall Supported Hypercalls
+ *
+ * Xen on ARM makes extensive use of hardware facilities and therefore
+ * only a subset of the potential hypercalls are required.
+ *
+ * Since ARM uses second stage paging any machine/physical addresses
+ * passed to hypercalls are Guest Physical Addresses (Intermediate
+ * Physical Addresses) unless otherwise noted.
+ *
+ * The following hypercalls (and sub operations) are supported on the
+ * ARM platform. Other hypercalls should be considered
+ * unavailable/unsupported.
+ *
+ *  HYPERVISOR_memory_op
+ *   All generic sub-operations.
+ *
+ *   In addition the following arch specific sub-ops:
+ *    * XENMEM_add_to_physmap
+ *    * XENMEM_add_to_physmap_range
+ *
+ *  HYPERVISOR_domctl
+ *   All generic sub-operations, with the exception of:
+ *    * XEN_DOMCTL_iomem_permission (not yet implemented)
+ *    * XEN_DOMCTL_irq_permission (not yet implemented)
+ *
+ *  HYPERVISOR_sched_op
+ *   All generic sub-operations, with the exception of:
+ *    * SCHEDOP_block -- prefer wfi hardware instruction
+ *
+ *  HYPERVISOR_console_io
+ *   All generic sub-operations
+ *
+ *  HYPERVISOR_xen_version
+ *   All generic sub-operations
+ *
+ *  HYPERVISOR_event_channel_op
+ *   All generic sub-operations
+ *
+ *  HYPERVISOR_physdev_op
+ *   No sub-operations are currenty supported
+ *
+ *  HYPERVISOR_sysctl
+ *   All generic sub-operations, with the exception of:
+ *    * XEN_SYSCTL_page_offline_op
+ *    * XEN_SYSCTL_get_pmstat
+ *    * XEN_SYSCTL_pm_op
+ *
+ *  HYPERVISOR_hvm_op
+ *   Exactly these sub-operations are supported:
+ *    * HVMOP_set_param
+ *    * HVMOP_get_param
+ *
+ *  HYPERVISOR_grant_table_op
+ *   All generic sub-operations
+ *
+ *  HYPERVISOR_vcpu_op
+ *   Exactly these sub-operations are supported:
+ *    * VCPUOP_register_vcpu_info
+ *    * VCPUOP_register_runstate_memory_area
+ */
+
 #define XEN_HYPERCALL_TAG   0XEA1
 
 #define uint64_aligned_t uint64_t __attribute__((aligned(8)))