[PATCH v15 1/3] mem_sharing: don't reset vCPU info page during fork reset

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>]

When a forked VM is being reset while having vm_events active, re-copying the
vCPU info page can lead to events being lost. This seems to only affect a
subset of events (interrupts), while not others (cpuid, MTF, EPT) thus it was
not discovered beforehand. Only copying vCPU info page contents during initial
fork fixes the problem.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
---
 xen/arch/x86/mm/mem_sharing.c | 50 +++++++++++++++++------------------
 1 file changed, 25 insertions(+), 25 deletions(-)

diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index e572e9e39d..4b31a8b8f6 100644
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -1534,28 +1534,6 @@ int mem_sharing_fork_page(struct domain *d, gfn_t gfn, 
bool unsharing)
                           p2m->default_access, -1);
 }
 
-static int bring_up_vcpus(struct domain *cd, struct domain *d)
-{
-    unsigned int i;
-    int ret = -EINVAL;
-
-    if ( d->max_vcpus != cd->max_vcpus ||
-        (ret = cpupool_move_domain(cd, d->cpupool)) )
-        return ret;
-
-    for ( i = 0; i < cd->max_vcpus; i++ )
-    {
-        if ( !d->vcpu[i] || cd->vcpu[i] )
-            continue;
-
-        if ( !vcpu_create(cd, i) )
-            return -EINVAL;
-    }
-
-    domain_update_node_affinity(cd);
-    return 0;
-}
-
 static int copy_vcpu_settings(struct domain *cd, const struct domain *d)
 {
     unsigned int i;
@@ -1614,6 +1592,31 @@ static int copy_vcpu_settings(struct domain *cd, const 
struct domain *d)
     return 0;
 }
 
+static int bring_up_vcpus(struct domain *cd, struct domain *d)
+{
+    unsigned int i;
+    int ret = -EINVAL;
+
+    if ( d->max_vcpus != cd->max_vcpus ||
+        (ret = cpupool_move_domain(cd, d->cpupool)) )
+        return ret;
+
+    for ( i = 0; i < cd->max_vcpus; i++ )
+    {
+        if ( !d->vcpu[i] || cd->vcpu[i] )
+            continue;
+
+        if ( !vcpu_create(cd, i) )
+            return -EINVAL;
+    }
+
+    if ( (ret = copy_vcpu_settings(cd, d)) )
+        return ret;
+
+    domain_update_node_affinity(cd);
+    return 0;
+}
+
 static int fork_hap_allocation(struct domain *cd, struct domain *d)
 {
     int rc;
@@ -1697,9 +1700,6 @@ static int copy_settings(struct domain *cd, struct domain 
*d)
 {
     int rc;
 
-    if ( (rc = copy_vcpu_settings(cd, d)) )
-        return rc;
-
     if ( (rc = hvm_copy_context_and_params(cd, d)) )
         return rc;
 
-- 
2.20.1