[PATCH 3/3] xen/vm_event: Add safe to disable vm_event

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

Instead of having to repeatedly try to disable vm_events, request a specific
vm_event to be sent when the domain is safe to continue with shutting down
the vm_event interface.

Signed-off-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c            | 38 ++++++++++++++++++++++++++-----
 xen/arch/x86/hvm/monitor.c        | 14 ++++++++++++
 xen/arch/x86/monitor.c            | 13 +++++++++++
 xen/include/asm-x86/domain.h      |  1 +
 xen/include/asm-x86/hvm/monitor.h |  1 +
 xen/include/public/domctl.h       |  2 ++
 xen/include/public/vm_event.h     |  8 +++++++
 7 files changed, 71 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 063f8ddc18..50c67e7b8e 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -563,15 +563,41 @@ void hvm_do_resume(struct vcpu *v)
         v->arch.hvm.inject_event.vector = HVM_EVENT_VECTOR_UNSET;
     }
 
-    if ( unlikely(v->arch.vm_event) && v->arch.monitor.next_interrupt_enabled )
+    if ( unlikely(v->arch.vm_event) )
     {
-        struct x86_event info;
+        struct domain *d = v->domain;
+
+        if ( v->arch.monitor.next_interrupt_enabled )
+        {
+            struct x86_event info;
+
+            if ( hvm_get_pending_event(v, &info) )
+            {
+                hvm_monitor_interrupt(info.vector, info.type, info.error_code,
+                                      info.cr2);
+                v->arch.monitor.next_interrupt_enabled = false;
+            }
+        }
 
-        if ( hvm_get_pending_event(v, &info) )
+        if ( d->arch.monitor.safe_to_disable )
         {
-            hvm_monitor_interrupt(info.vector, info.type, info.error_code,
-                                  info.cr2);
-            v->arch.monitor.next_interrupt_enabled = false;
+            struct vcpu *check_vcpu;
+            bool pending_op = false;
+
+            for_each_vcpu ( d, check_vcpu )
+            {
+                if ( vm_event_check_pending_op(check_vcpu) )
+                {
+                    pending_op = true;
+                    break;
+                }
+            }
+
+            if ( !pending_op )
+            {
+                hvm_monitor_safe_to_disable();
+                d->arch.monitor.safe_to_disable = false;
+            }
         }
     }
 }
diff --git a/xen/arch/x86/hvm/monitor.c b/xen/arch/x86/hvm/monitor.c
index f5d89e71d1..8e67dd1a0b 100644
--- a/xen/arch/x86/hvm/monitor.c
+++ b/xen/arch/x86/hvm/monitor.c
@@ -300,6 +300,20 @@ bool hvm_monitor_check_p2m(unsigned long gla, gfn_t gfn, 
uint32_t pfec,
     return monitor_traps(curr, true, &req) >= 0;
 }
 
+bool hvm_monitor_safe_to_disable(void)
+{
+    struct vcpu *curr = current;
+    struct arch_domain *ad = &curr->domain->arch;
+    vm_event_request_t req = {};
+
+    if ( !ad->monitor.safe_to_disable )
+        return 0;
+
+    req.reason = VM_EVENT_REASON_SAFE_TO_DISABLE;
+
+    return monitor_traps(curr, 0, &req);
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/x86/monitor.c b/xen/arch/x86/monitor.c
index 1517a97f50..86e0ba2fbc 100644
--- a/xen/arch/x86/monitor.c
+++ b/xen/arch/x86/monitor.c
@@ -339,6 +339,19 @@ int arch_monitor_domctl_event(struct domain *d,
         break;
     }
 
+    case XEN_DOMCTL_MONITOR_EVENT_SAFE_TO_DISABLE:
+    {
+        bool old_status = ad->monitor.safe_to_disable;
+
+        if ( unlikely(old_status == requested_status) )
+            return -EEXIST;
+
+        domain_pause(d);
+        ad->monitor.safe_to_disable = requested_status;
+        domain_unpause(d);
+        break;
+    }
+
     default:
         /*
          * Should not be reached unless arch_monitor_get_capabilities() is
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index d890ab7a22..948b750c71 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -417,6 +417,7 @@ struct arch_domain
          */
         unsigned int inguest_pagefault_disabled                            : 1;
         unsigned int control_register_values                               : 1;
+        unsigned int safe_to_disable                                       : 1;
         struct monitor_msr_bitmap *msr_bitmap;
         uint64_t write_ctrlreg_mask[4];
     } monitor;
diff --git a/xen/include/asm-x86/hvm/monitor.h 
b/xen/include/asm-x86/hvm/monitor.h
index 66de24cb75..194e2f857e 100644
--- a/xen/include/asm-x86/hvm/monitor.h
+++ b/xen/include/asm-x86/hvm/monitor.h
@@ -52,6 +52,7 @@ bool hvm_monitor_emul_unimplemented(void);
 
 bool hvm_monitor_check_p2m(unsigned long gla, gfn_t gfn, uint32_t pfec,
                            uint16_t kind);
+bool hvm_monitor_safe_to_disable(void);
 
 #endif /* __ASM_X86_HVM_MONITOR_H__ */
 
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index cbcd25f12c..247e809a6c 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -1040,6 +1040,8 @@ struct xen_domctl_psr_cmt_op {
 #define XEN_DOMCTL_MONITOR_EVENT_EMUL_UNIMPLEMENTED    10
 /* Enabled by default */
 #define XEN_DOMCTL_MONITOR_EVENT_INGUEST_PAGEFAULT     11
+/* Always async, disables automaticaly on first event */
+#define XEN_DOMCTL_MONITOR_EVENT_SAFE_TO_DISABLE       12
 
 struct xen_domctl_monitor_op {
     uint32_t op; /* XEN_DOMCTL_MONITOR_OP_* */
diff --git a/xen/include/public/vm_event.h b/xen/include/public/vm_event.h
index fdd3ad8a30..b66d2a8634 100644
--- a/xen/include/public/vm_event.h
+++ b/xen/include/public/vm_event.h
@@ -159,6 +159,14 @@
 #define VM_EVENT_REASON_DESCRIPTOR_ACCESS       13
 /* Current instruction is not implemented by the emulator */
 #define VM_EVENT_REASON_EMUL_UNIMPLEMENTED      14
+/*
+ * When shutting down vm_event it may not be immediately safe to complete the
+ * process as some vCPUs may be pending synchronization. This async event
+ * type can be used to receive a notification when its safe to finish disabling
+ * the vm_event interface. All other event types need to be disabled before
+ * registering to this one.
+ */
+#define VM_EVENT_REASON_SAFE_TO_DISABLE         15
 
 /* Supported values for the vm_event_write_ctrlreg index. */
 #define VM_EVENT_X86_CR0    0
-- 
2.26.1