[Xen-devel] [PATCH v5 2/7] VMX: Properly handle pi when all the assigned devices are removed

[Feng Wu <feng.wu@xxxxxxxxx>]

This patch handles some concern cases when the last assigned device
is removed from the domain. In this case we should carefully handle
pi descriptor and the per-cpu blocking list, to make sure:
- all the PI descriptor are in the right state when next time a
devices is assigned to the domain again.
- No remaining vcpus of the domain in the per-cpu blocking list.

Here we call vmx_pi_list_remove() to remove the vCPU from the blocking list
if it is on the list. However, this could happen when vmx_vcpu_block() is
being called, hence we might incorrectly add the vCPU to the blocking list
while the last devcie is detached from the domain. Consider that the situation
can only occur when detaching the last device from the domain and it is not
a frequent operation, so we use domain_pause before that, which is considered
as an clean and maintainable solution for the situation.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
v5:
- Remove a no-op wrapper

 xen/arch/x86/hvm/vmx/vmx.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 623d5bc..d210516 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -163,14 +163,12 @@ static void vmx_pi_switch_to(struct vcpu *v)
     pi_clear_sn(pi_desc);
 }
 
-static void vmx_pi_do_resume(struct vcpu *v)
+static void vmx_pi_list_remove(struct vcpu *v)
 {
     unsigned long flags;
     spinlock_t *pi_blocking_list_lock;
     struct pi_desc *pi_desc = &v->arch.hvm_vmx.pi_desc;
 
-    ASSERT(!test_bit(_VPF_blocked, &v->pause_flags));
-
     /*
      * Set 'NV' field back to posted_intr_vector, so the
      * Posted-Interrupts can be delivered to the vCPU when
@@ -178,12 +176,12 @@ static void vmx_pi_do_resume(struct vcpu *v)
      */
     write_atomic(&pi_desc->nv, posted_intr_vector);
 
-    /* The vCPU is not on any blocking list. */
     pi_blocking_list_lock = v->arch.hvm_vmx.pi_blocking.lock;
 
     /* Prevent the compiler from eliminating the local variable.*/
     smp_rmb();
 
+    /* The vCPU is not on any blocking list. */
     if ( pi_blocking_list_lock == NULL )
         return;
 
@@ -203,6 +201,13 @@ static void vmx_pi_do_resume(struct vcpu *v)
     spin_unlock_irqrestore(pi_blocking_list_lock, flags);
 }
 
+static void vmx_pi_do_resume(struct vcpu *v)
+{
+    ASSERT(!test_bit(_VPF_blocked, &v->pause_flags));
+
+    vmx_pi_list_remove(v);
+}
+
 /* This function is called when pcidevs_lock is held */
 void vmx_pi_hooks_assign(struct domain *d)
 {
@@ -220,14 +225,29 @@ void vmx_pi_hooks_assign(struct domain *d)
 /* This function is called when pcidevs_lock is held */
 void vmx_pi_hooks_deassign(struct domain *d)
 {
+    struct vcpu *v;
+
     if ( !iommu_intpost || !has_hvm_container_domain(d) )
         return;
 
     ASSERT(d->arch.hvm_domain.vmx.vcpu_block);
 
+    /*
+     * Pausing the domain can make sure the vCPU is not
+     * running and hence calling the hooks simultaneously
+     * when deassigning the PI hooks and removing the vCPU
+     * from the blocking list.
+     */
+    domain_pause(d);
+
     d->arch.hvm_domain.vmx.vcpu_block = NULL;
     d->arch.hvm_domain.vmx.pi_do_resume = NULL;
     d->arch.hvm_domain.vmx.pi_switch_from = NULL;
+
+    for_each_vcpu ( d, v )
+        vmx_pi_list_remove(v);
+
+    domain_unpause(d);
 }
 
 static int vmx_domain_initialise(struct domain *d)
-- 
2.1.0


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