[xen master] x86: introduce GADDR based secondary time area registration alternative

[patchbot@xxxxxxx]

commit 60e544a8c58fdc720de05f6a721178f9516436d1
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Oct 2 17:11:26 2023 +0200
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Thu Oct 5 14:10:45 2023 +0100

    x86: introduce GADDR based secondary time area registration alternative
    
    The registration by virtual/linear address has downsides: 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 secondary time
    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/domain.c             | 28 ++++++++++++++++++++++++++++
 xen/arch/x86/include/asm/domain.h |  2 ++
 xen/arch/x86/time.c               | 10 ++++++++++
 xen/arch/x86/x86_64/domain.c      |  1 +
 xen/include/public/vcpu.h         |  4 ++++
 5 files changed, 45 insertions(+)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 9d352defa2..8e0af22781 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1529,6 +1529,15 @@ int arch_vcpu_reset(struct vcpu *v)
     return 0;
 }
 
+static void cf_check
+time_area_populate(void *map, struct vcpu *v)
+{
+    if ( is_pv_vcpu(v) )
+        v->arch.pv.pending_system_time.version = 0;
+
+    force_update_secondary_system_time(v, map);
+}
+
 long do_vcpu_op(int cmd, unsigned int vcpuid, XEN_GUEST_HANDLE_PARAM(void) arg)
 {
     long rc = 0;
@@ -1567,6 +1576,25 @@ long do_vcpu_op(int cmd, unsigned int vcpuid, 
XEN_GUEST_HANDLE_PARAM(void) arg)
         break;
     }
 
+    case VCPUOP_register_vcpu_time_phys_area:
+    {
+        struct vcpu_register_time_memory_area area;
+
+        rc = -EFAULT;
+        if ( copy_from_guest(&area.addr.p, arg, 1) )
+            break;
+
+        rc = map_guest_area(v, area.addr.p,
+                            sizeof(vcpu_time_info_t),
+                            &v->arch.time_guest_area,
+                            time_area_populate);
+        if ( rc == -ERESTART )
+            rc = hypercall_create_continuation(__HYPERVISOR_vcpu_op, "iih",
+                                               cmd, vcpuid, arg);
+
+        break;
+    }
+
     case VCPUOP_get_physid:
     {
         struct vcpu_get_physid cpu_id;
diff --git a/xen/arch/x86/include/asm/domain.h 
b/xen/arch/x86/include/asm/domain.h
index e0bd28e424..619e667938 100644
--- a/xen/arch/x86/include/asm/domain.h
+++ b/xen/arch/x86/include/asm/domain.h
@@ -692,6 +692,8 @@ void domain_cpu_policy_changed(struct domain *d);
 
 bool update_secondary_system_time(struct vcpu *,
                                   struct vcpu_time_info *);
+void force_update_secondary_system_time(struct vcpu *,
+                                        struct vcpu_time_info *);
 
 void vcpu_show_registers(const struct vcpu *);
 
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 332d2d79ae..73df1639a3 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -1628,6 +1628,16 @@ void force_update_vcpu_system_time(struct vcpu *v)
     __update_vcpu_system_time(v, 1);
 }
 
+void force_update_secondary_system_time(struct vcpu *v,
+                                        struct vcpu_time_info *map)
+{
+    struct vcpu_time_info u;
+
+    collect_time_info(v, &u);
+    u.version = -1; /* Compensate for version_update_end(). */
+    write_time_guest_area(map, &u);
+}
+
 static void update_domain_rtc(void)
 {
     struct domain *d;
diff --git a/xen/arch/x86/x86_64/domain.c b/xen/arch/x86/x86_64/domain.c
index 494b0b54e6..a02d4f569e 100644
--- a/xen/arch/x86/x86_64/domain.c
+++ b/xen/arch/x86/x86_64/domain.c
@@ -115,6 +115,7 @@ compat_vcpu_op(int cmd, unsigned int vcpuid, 
XEN_GUEST_HANDLE_PARAM(void) arg)
 
     case VCPUOP_send_nmi:
     case VCPUOP_get_physid:
+    case VCPUOP_register_vcpu_time_phys_area:
         rc = do_vcpu_op(cmd, vcpuid, arg);
         break;
 
diff --git a/xen/include/public/vcpu.h b/xen/include/public/vcpu.h
index 9dac0f9748..8fb0bd1b6c 100644
--- a/xen/include/public/vcpu.h
+++ b/xen/include/public/vcpu.h
@@ -209,6 +209,9 @@ DEFINE_XEN_GUEST_HANDLE(vcpu_get_physid_t);
  * segment limit).  It can then apply the normal algorithm to compute
  * system time from the tsc.
  *
+ * New code wants to prefer VCPUOP_register_vcpu_time_phys_area, and only
+ * fall back to the operation here for backwards compatibility.
+ *
  * @extra_arg == pointer to vcpu_register_time_info_memory_area structure.
  */
 #define VCPUOP_register_vcpu_time_memory_area   13
@@ -235,6 +238,7 @@ DEFINE_XEN_GUEST_HANDLE(vcpu_register_time_memory_area_t);
  * VMASST_TYPE_runstate_update_flag engaged by the domain.
  */
 #define VCPUOP_register_runstate_phys_area      14
+#define VCPUOP_register_vcpu_time_phys_area     15
 
 #endif /* __XEN_PUBLIC_VCPU_H__ */
 
--
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