[Xen-devel] [PATCH v3 2/2] xen: add update indicator to vcpu_runstate_info

[Juergen Gross <jgross@xxxxxxxx>]

In order to support reading another vcpu's mapped vcpu_runstate_info
an indicator for an occurring update of the runstate information is
needed.

Add the possibility to activate setting this indicator in the highest
bit of state_entry_time via a vm_assist hypercall. When activated the
update indicator will be set before the runstate information is
modified in guest memory and it will be reset after modification is
done. As state_entry_time is guaranteed to be different after each
update the guest can detect any update (either in progress or while
reading the runstate data) by comparing state_entry_time before and
after reading runstate data: in case the values differ or the update
indicator was set the data might be inconsistent and should be reread.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V3: simplify update_runstate_area() address calculation as requested
    by Jan Beulich

V2: smp_wmb() instead of wmb() as requested by Andrew Cooper
    use sizeof() as requested by Jan Beulich
    eliminate new variable update_flag as requested by Jan Beulich
---
 xen/arch/arm/domain.c        | 20 ++++++++++++++++++++
 xen/arch/x86/domain.c        | 21 +++++++++++++++++++++
 xen/include/asm-arm/config.h |  2 +-
 xen/include/asm-x86/config.h |  1 +
 xen/include/public/vcpu.h    |  6 ++++++
 xen/include/public/xen.h     |  7 +++++++
 6 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 1365b4a..2ace1bc 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -239,10 +239,30 @@ static void ctxt_switch_to(struct vcpu *n)
 /* Update per-VCPU guest runstate shared memory area (if registered). */
 static void update_runstate_area(struct vcpu *v)
 {
+    void __user *guest_handle = NULL;
+
     if ( guest_handle_is_null(runstate_guest(v)) )
         return;
 
+    if ( VM_ASSIST(v->domain, runstate_update_flag) )
+    {
+        guest_handle = &v->runstate_guest.p->state_entry_time + 1;
+        guest_handle--;
+        v->runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
+        __raw_copy_to_guest(guest_handle,
+                            (void *)(&v->runstate.state_entry_time + 1) - 1, 
1);
+        smp_wmb();
+    }
+
     __copy_to_guest(runstate_guest(v), &v->runstate, 1);
+
+    if ( guest_handle )
+    {
+        v->runstate.state_entry_time &= ~XEN_RUNSTATE_UPDATE;
+        smp_wmb();
+        __raw_copy_to_guest(guest_handle,
+                            (void *)(&v->runstate.state_entry_time + 1) - 1, 
1);
+    }
 }
 
 static void schedule_tail(struct vcpu *prev)
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 989bc74..3ba7ed1 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1926,12 +1926,25 @@ bool_t update_runstate_area(struct vcpu *v)
 {
     bool_t rc;
     smap_check_policy_t smap_policy;
+    void __user *guest_handle = NULL;
 
     if ( guest_handle_is_null(runstate_guest(v)) )
         return 1;
 
     smap_policy = smap_policy_change(v, SMAP_CHECK_ENABLED);
 
+    if ( VM_ASSIST(v->domain, runstate_update_flag) )
+    {
+        guest_handle = has_32bit_shinfo(v->domain)
+            ? &v->runstate_guest.compat.p->state_entry_time + 1
+            : &v->runstate_guest.native.p->state_entry_time + 1;
+        guest_handle--;
+        v->runstate.state_entry_time |= XEN_RUNSTATE_UPDATE;
+        __raw_copy_to_guest(guest_handle,
+                            (void *)(&v->runstate.state_entry_time + 1) - 1, 
1);
+        smp_wmb();
+    }
+
     if ( has_32bit_shinfo(v->domain) )
     {
         struct compat_vcpu_runstate_info info;
@@ -1944,6 +1957,14 @@ bool_t update_runstate_area(struct vcpu *v)
         rc = __copy_to_guest(runstate_guest(v), &v->runstate, 1) !=
              sizeof(v->runstate);
 
+    if ( guest_handle )
+    {
+        v->runstate.state_entry_time &= ~XEN_RUNSTATE_UPDATE;
+        smp_wmb();
+        __raw_copy_to_guest(guest_handle,
+                            (void *)(&v->runstate.state_entry_time + 1) - 1, 
1);
+    }
+
     smap_policy_change(v, smap_policy);
 
     return rc;
diff --git a/xen/include/asm-arm/config.h b/xen/include/asm-arm/config.h
index 563f49b..ce3edc2 100644
--- a/xen/include/asm-arm/config.h
+++ b/xen/include/asm-arm/config.h
@@ -199,7 +199,7 @@ extern unsigned long frametable_virt_end;
 #define watchdog_disable() ((void)0)
 #define watchdog_enable()  ((void)0)
 
-#define VM_ASSIST_VALID          (0)
+#define VM_ASSIST_VALID          (1UL << VMASST_TYPE_runstate_update_flag)
 
 #endif /* __ARM_CONFIG_H__ */
 /*
diff --git a/xen/include/asm-x86/config.h b/xen/include/asm-x86/config.h
index c10129d..6fd84e7 100644
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -332,6 +332,7 @@ extern unsigned long xen_phys_start;
                                   (1UL << VMASST_TYPE_writable_pagetables) | \
                                   (1UL << VMASST_TYPE_pae_extended_cr3)    | \
                                   (1UL << VMASST_TYPE_architectural_iopl)  | \
+                                  (1UL << VMASST_TYPE_runstate_update_flag)| \
                                   (1UL << VMASST_TYPE_m2p_strict))
 #define VM_ASSIST_VALID          NATIVE_VM_ASSIST_VALID
 #define COMPAT_VM_ASSIST_VALID   (NATIVE_VM_ASSIST_VALID & \
diff --git a/xen/include/public/vcpu.h b/xen/include/public/vcpu.h
index 692b87a..2aa230d 100644
--- a/xen/include/public/vcpu.h
+++ b/xen/include/public/vcpu.h
@@ -84,6 +84,12 @@ struct vcpu_runstate_info {
     /* When was current state entered (system time, ns)? */
     uint64_t state_entry_time;
     /*
+     * Update indicator set in state_entry_time:
+     * When activated via VMASST_TYPE_runstate_update_flag, set during
+     * updates in guest memory mapped copy of vcpu_runstate_info.
+     */
+#define XEN_RUNSTATE_UPDATE          (1ULL << 63)
+    /*
      * Time spent in each RUNSTATE_* (ns). The sum of these times is
      * guaranteed not to drift from system time.
      */
diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
index 37bbb22..b9e5e0f 100644
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -510,6 +510,13 @@ DEFINE_XEN_GUEST_HANDLE(mmuext_op_t);
 #define VMASST_TYPE_architectural_iopl   4
 
 /*
+ * All guests: activate update indicator in vcpu_runstate_info
+ * Enable setting the XEN_RUNSTATE_UPDATE flag in guest memory mapped
+ * vcpu_runstate_info during updates of the runstate information.
+ */
+#define VMASST_TYPE_runstate_update_flag 5
+
+/*
  * x86/64 guests: strictly hide M2P from user mode.
  * This allows the guest to control respective hypervisor behavior:
  * - when not set, L4 tables get created with the respective slot blank,
-- 
2.6.6


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