x86, hvm: Fix double-free of vpmu->context

When `opcontrol --shutdown' is called after xenoprof is used on Dom0,
the vpmu owner becomes PMU_OWNER_NONE. So it is possible to acquire
the owner as PMU_OWNER_HVM and to allocate vpmu->context twice. As a
result, the hypervisor panics because of double-alloc/free of
vpmu->context.

Signed-off-by: Kazuhiro Suzuki <kaz@jp.fujitsu.com>

xen/arch/x86/hvm/vmx/vpmu_core2.c

@@ -296,7 +296,8 @@ static int core2_vpmu_msr_common_check(u32 msr_index, int *type, int *index)
         return 0;
 
     if ( unlikely(!(vpmu->flags & VPMU_CONTEXT_ALLOCATED)) &&
-         !core2_vpmu_alloc_resource(current) )
+	 (vpmu->context != NULL ||
+	  !core2_vpmu_alloc_resource(current)) )
         return 0;
     vpmu->flags |= VPMU_CONTEXT_ALLOCATED;
 
@@ -488,6 +489,7 @@ static void core2_vpmu_destroy(struct vcpu *v)
     if ( cpu_has_vmx_msr_bitmap )
         core2_vpmu_unset_msr_bitmap(v->arch.hvm_vmx.msr_bitmap);
     release_pmu_ownship(PMU_OWNER_HVM);
+    vpmu->flags &= ~VPMU_CONTEXT_ALLOCATED;
 }
 
 struct arch_vpmu_ops core2_vpmu_ops = {

xen/arch/x86/oprofile/op_model_ppro.c

@@ -219,6 +219,8 @@ static void ppro_free_msr(struct vcpu *v)
 {
 	struct vpmu_struct *vpmu = vcpu_vpmu(v);
 
+	if ( !(vpmu->flags & PASSIVE_DOMAIN_ALLOCATED) )
+		return;
 	xfree(vpmu->context);
 	vpmu->flags &= ~PASSIVE_DOMAIN_ALLOCATED;
 }