Sync against scheduler tail on other CPUs when context

switching to a new VCPU. Otherwise we cannot pull the
VCPU's state off the other CPU.

Signed-off-by: Keir Fraser <keir@xensource.com>

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index b38147211adc19de7e17a6064b10fdbbdec0c685..25746ab4f1c8ab62a965584824b388c9ee14158c 100644 (file)
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -738,8 +738,12 @@ void context_switch(struct vcpu *prev, struct vcpu *next)
     ASSERT(cpus_weight(dirty_mask) <= 1);
     if ( unlikely(!cpu_isset(cpu, dirty_mask) && !cpus_empty(dirty_mask)) )
     {
+        /* Make sure the next VCPU is not in a scheduling tail. */
+        while ( test_bit(_VCPUF_running, &next->vcpu_flags) )
+            cpu_relax();
         /* Other cpus call __sync_lazy_execstate from flush ipi handler. */
-        flush_tlb_mask(dirty_mask);
+        if ( !cpus_empty(next->vcpu_dirty_cpumask) )
+            flush_tlb_mask(next->vcpu_dirty_cpumask);
     }
 
     local_irq_disable();