[xen master] domain: introduce GADDR based runstate area registration alternative

[patchbot@xxxxxxx]

commit d5df44275e7af690ef18b56cc58762ce33a37149
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Oct 2 17:11:25 2023 +0200
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Thu Oct 5 14:10:45 2023 +0100

    domain: introduce GADDR based runstate area registration alternative
    
    The registration by virtual/linear address has downsides: At least on
    x86 the access is expensive for HVM/PVH domains. Furthermore for 64-bit
    PV domains the area is inaccessible (and hence cannot be updated by Xen)
    when in guest-user mode.
    
    Introduce a new vCPU operation allowing to register the runstate area by
    guest-physical address.
    
    An at least theoretical downside to using physically registered areas is
    that PV then won't see dirty (and perhaps also accessed) bits set in its
    respective page table entries.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
    Release-acked-by: Henry Wang <Henry.Wang@xxxxxxx>
---
 xen/arch/x86/x86_64/domain.c | 35 +++++++++++++++++++++++++++++++++++
 xen/common/domain.c          | 39 +++++++++++++++++++++++++++++++++++++++
 xen/include/public/vcpu.h    | 15 +++++++++++++++
 3 files changed, 89 insertions(+)

diff --git a/xen/arch/x86/x86_64/domain.c b/xen/arch/x86/x86_64/domain.c
index bfaea17fe7..494b0b54e6 100644
--- a/xen/arch/x86/x86_64/domain.c
+++ b/xen/arch/x86/x86_64/domain.c
@@ -12,6 +12,22 @@
 CHECK_vcpu_get_physid;
 #undef xen_vcpu_get_physid
 
+static void cf_check
+runstate_area_populate(void *map, struct vcpu *v)
+{
+    if ( is_pv_vcpu(v) )
+        v->arch.pv.need_update_runstate_area = false;
+
+    v->runstate_guest_area_compat = true;
+
+    if ( v == current )
+    {
+        struct compat_vcpu_runstate_info *info = map;
+
+        XLAT_vcpu_runstate_info(info, &v->runstate);
+    }
+}
+
 int
 compat_vcpu_op(int cmd, unsigned int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg)
 {
@@ -58,6 +74,25 @@ compat_vcpu_op(int cmd, unsigned int vcpuid, 
XEN_GUEST_HANDLE_PARAM(void) arg)
         break;
     }
 
+    case VCPUOP_register_runstate_phys_area:
+    {
+        struct compat_vcpu_register_runstate_memory_area area;
+
+        rc = -EFAULT;
+        if ( copy_from_guest(&area.addr.p, arg, 1) )
+            break;
+
+        rc = map_guest_area(v, area.addr.p,
+                            sizeof(struct compat_vcpu_runstate_info),
+                            &v->runstate_guest_area,
+                            runstate_area_populate);
+        if ( rc == -ERESTART )
+            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
+                                               cmd, vcpuid, arg);
+
+        break;
+    }
+
     case VCPUOP_register_vcpu_time_memory_area:
     {
         struct compat_vcpu_register_time_memory_area area = { .addr.p = 0 };
diff --git a/xen/common/domain.c b/xen/common/domain.c
index 747bf5c87a..486c1ae3f7 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -1830,6 +1830,26 @@ bool update_runstate_area(struct vcpu *v)
     return rc;
 }
 
+static void cf_check
+runstate_area_populate(void *map, struct vcpu *v)
+{
+#ifdef CONFIG_PV
+    if ( is_pv_vcpu(v) )
+        v->arch.pv.need_update_runstate_area = false;
+#endif
+
+#ifdef CONFIG_COMPAT
+    v->runstate_guest_area_compat = false;
+#endif
+
+    if ( v == current )
+    {
+        struct vcpu_runstate_info *info = map;
+
+        *info = v->runstate;
+    }
+}
+
 long common_vcpu_op(int cmd, struct vcpu *v, XEN_GUEST_HANDLE_PARAM(void) arg)
 {
     long rc = 0;
@@ -2012,6 +2032,25 @@ long common_vcpu_op(int cmd, struct vcpu *v, 
XEN_GUEST_HANDLE_PARAM(void) arg)
         break;
     }
 
+    case VCPUOP_register_runstate_phys_area:
+    {
+        struct vcpu_register_runstate_memory_area area;
+
+        rc = -EFAULT;
+        if ( copy_from_guest(&area.addr.p, arg, 1) )
+            break;
+
+        rc = map_guest_area(v, area.addr.p,
+                            sizeof(struct vcpu_runstate_info),
+                            &v->runstate_guest_area,
+                            runstate_area_populate);
+        if ( rc == -ERESTART )
+            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
+                                               cmd, vcpuid, arg);
+
+        break;
+    }
+
     default:
         rc = -ENOSYS;
         break;
diff --git a/xen/include/public/vcpu.h b/xen/include/public/vcpu.h
index a836b264a9..9dac0f9748 100644
--- a/xen/include/public/vcpu.h
+++ b/xen/include/public/vcpu.h
@@ -110,6 +110,8 @@ DEFINE_XEN_GUEST_HANDLE(vcpu_runstate_info_t);
  *     runstate.state will always be RUNSTATE_running and
  *     runstate.state_entry_time will indicate the system time at which the
  *     VCPU was last scheduled to run.
+ *  3. New code wants to prefer VCPUOP_register_runstate_phys_area, and only
+ *     fall back to the operation here for backwards compatibility.
  * @extra_arg == pointer to vcpu_register_runstate_memory_area structure.
  */
 #define VCPUOP_register_runstate_memory_area 5
@@ -221,6 +223,19 @@ struct vcpu_register_time_memory_area {
 typedef struct vcpu_register_time_memory_area vcpu_register_time_memory_area_t;
 DEFINE_XEN_GUEST_HANDLE(vcpu_register_time_memory_area_t);
 
+/*
+ * Like the respective VCPUOP_register_*_memory_area, just using the "addr.p"
+ * field of the supplied struct as a guest physical address (i.e. in GFN 
space).
+ * The respective area may not cross a page boundary.  Pass ~0 to unregister an
+ * area.  Note that as long as an area is registered by physical address, the
+ * linear address based area will not be serviced (updated) by the hypervisor.
+ *
+ * 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.
+ */
+#define VCPUOP_register_runstate_phys_area      14
+
 #endif /* __XEN_PUBLIC_VCPU_H__ */
 
 /*
--
generated by git-patchbot for /home/xen/git/xen.git#master