[Xen-devel] [PATCH for 4.5] x86/VPMU: Clear last_vcpu when destroying VPMU

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

We need to make sure that last_vcpu is not pointing to VCPU whose
VPMU is being destroyed. Otherwise we may try dereference it in
the future, when VCPU is gone.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vpmu.c |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)

This needs to be backported to 4.3 and 4.4 as well

diff --git a/xen/arch/x86/hvm/vpmu.c b/xen/arch/x86/hvm/vpmu.c
index 1df74c2..6d39680 100644
--- a/xen/arch/x86/hvm/vpmu.c
+++ b/xen/arch/x86/hvm/vpmu.c
@@ -247,10 +247,32 @@ void vpmu_initialise(struct vcpu *v)
     }
 }
 
+static void vpmu_clear_last(void *arg)
+{
+    struct vcpu *v = (struct vcpu *)arg;
+
+    if ( this_cpu(last_vcpu) == v )
+        this_cpu(last_vcpu) = NULL;
+}
+
 void vpmu_destroy(struct vcpu *v)
 {
     struct vpmu_struct *vpmu = vcpu_vpmu(v);
 
+    if ( vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED) )
+    {
+        /* Need to clear last_vcpu in case it points to v */
+        if ( vpmu->last_pcpu != smp_processor_id() )
+            on_selected_cpus(cpumask_of(vpmu->last_pcpu),
+                             vpmu_clear_last, (void *)v, 1);
+        else
+        {
+            local_irq_disable();
+            vpmu_clear_last((void *)v);
+            local_irq_enable();
+        }
+    }
+
     if ( vpmu->arch_vpmu_ops && vpmu->arch_vpmu_ops->arch_vpmu_destroy )
         vpmu->arch_vpmu_ops->arch_vpmu_destroy(v);
 }
-- 
1.7.1


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