[PATCH v2 2/2] domain: expose newly introduced hypercalls as XENFEAT

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

XENFEAT_runstate_phys_area is exposed to all architectures, while
XENFEAT_vcpu_time_phys_area is currently only implemented for x86, and hence
the feature flag is also only exposed on x86.

Additionally add dummy guards with TODOs in the respective hypercall
implementations, to signal the intention to control the availability of those
hypercalls on a guest-by-guest basis from the toolstack.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v1:
 - Adjust comments, and add new one in vcpu.h
 - Add dummy guard with TDOD in hypercall implementations.
---
 CHANGELOG.md                  | 2 ++
 xen/arch/x86/domain.c         | 4 ++++
 xen/common/domain.c           | 4 ++++
 xen/common/kernel.c           | 6 +++++-
 xen/include/public/features.h | 9 +++++++++
 xen/include/public/vcpu.h     | 3 +++
 6 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e33cf4e1b113..47ea9e275462 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -31,6 +31,8 @@ The format is based on [Keep a 
Changelog](https://keepachangelog.com/en/1.0.0/)
  - Add Intel Hardware P-States (HWP) cpufreq driver.
  - On Arm, experimental support for dynamic addition/removal of Xen device tree
    nodes using a device tree overlay binary (.dtbo).
+ - Introduce two new hypercalls to map the vCPU runstate and time areas by
+   physical rather than linear/virtual addresses.
 
 ### Removed
  - On x86, the "pku" command line option has been removed.  It has never
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 8e0af2278104..8d3d52034a6d 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1580,6 +1580,10 @@ long do_vcpu_op(int cmd, unsigned int vcpuid, 
XEN_GUEST_HANDLE_PARAM(void) arg)
     {
         struct vcpu_register_time_memory_area area;
 
+        rc = -ENOSYS;
+        if ( 0 /* TODO: Dom's XENFEAT_vcpu_time_phys_area setting */ )
+            break;
+
         rc = -EFAULT;
         if ( copy_from_guest(&area.addr.p, arg, 1) )
             break;
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 1468638ade8b..8f9ab01c0cb7 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1998,6 +1998,10 @@ long common_vcpu_op(int cmd, struct vcpu *v, 
XEN_GUEST_HANDLE_PARAM(void) arg)
     {
         struct vcpu_register_runstate_memory_area area;
 
+        rc = -ENOSYS;
+        if ( 0 /* TODO: Dom's XENFEAT_runstate_phys_area setting */ )
+            break;
+
         rc = -EFAULT;
         if ( copy_from_guest(&area.addr.p, arg, 1) )
             break;
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index 52aa28762782..b6302e44b34e 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -607,7 +607,11 @@ long do_xen_version(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
arg)
         switch ( fi.submap_idx )
         {
         case 0:
-            fi.submap = (1U << XENFEAT_memory_op_vnode_supported);
+            fi.submap = (1U << XENFEAT_memory_op_vnode_supported) |
+#ifdef CONFIG_X86
+                        (1U << XENFEAT_vcpu_time_phys_area) |
+#endif
+                        (1U << XENFEAT_runstate_phys_area);
             if ( VM_ASSIST(d, pae_extended_cr3) )
                 fi.submap |= (1U << XENFEAT_pae_pgdir_above_4gb);
             if ( paging_mode_translate(d) )
diff --git a/xen/include/public/features.h b/xen/include/public/features.h
index d2a9175aae67..22713a51b520 100644
--- a/xen/include/public/features.h
+++ b/xen/include/public/features.h
@@ -111,6 +111,15 @@
 #define XENFEAT_not_direct_mapped         16
 #define XENFEAT_direct_mapped             17
 
+/*
+ * Signal whether the domain is permitted to use the following hypercalls:
+ *
+ * VCPUOP_register_runstate_phys_area
+ * VCPUOP_register_vcpu_time_phys_area
+ */
+#define XENFEAT_runstate_phys_area       18
+#define XENFEAT_vcpu_time_phys_area      19
+
 #define XENFEAT_NR_SUBMAPS 1
 
 #endif /* __XEN_PUBLIC_FEATURES_H__ */
diff --git a/xen/include/public/vcpu.h b/xen/include/public/vcpu.h
index 8fb0bd1b6c03..03b031a3e557 100644
--- a/xen/include/public/vcpu.h
+++ b/xen/include/public/vcpu.h
@@ -236,6 +236,9 @@ DEFINE_XEN_GUEST_HANDLE(vcpu_register_time_memory_area_t);
  * Note that the area registered via VCPUOP_register_runstate_memory_area will
  * be updated in the same manner as the one registered via virtual address PLUS
  * VMASST_TYPE_runstate_update_flag engaged by the domain.
+ *
+ * XENFEAT_{runstate,vcpu_time}_phys_area feature bits signal if the domain is
+ * permitted the usage of the hypercalls.
  */
 #define VCPUOP_register_runstate_phys_area      14
 #define VCPUOP_register_vcpu_time_phys_area     15
-- 
2.42.0