[Xen-devel] [PATCH v4 2/6] 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.

Basically, we pause the domain before zapping the PI hooks and
removing the vCPU from the blocking list, then unpause it after
that.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
v4:
- Rename some functions:
        vmx_pi_remove_vcpu_from_blocking_list() -> vmx_pi_list_remove()
        vmx_pi_blocking_cleanup() -> vmx_pi_list_cleanup()
- Remove the check in vmx_pi_list_cleanup()
- Comments adjustment

 xen/arch/x86/hvm/vmx/vmx.c | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 355936a..7305f40 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -158,14 +158,12 @@ 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
@@ -173,12 +171,12 @@ 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;
 
@@ -198,6 +196,18 @@ 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);
+}
+
+static void vmx_pi_list_cleanup(struct vcpu *v)
+{
+    vmx_pi_list_remove(v);
+}
+
 /* This function is called when pcidevs_lock is held */
 void vmx_pi_hooks_assign(struct domain *d)
 {
@@ -215,13 +225,28 @@ 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;
+
+    for_each_vcpu ( d, v )
+        vmx_pi_list_cleanup(v);
+
+    domain_unpause(d);
 }
 
 static int vmx_domain_initialise(struct domain *d)
-- 
2.1.0


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