[Xen-devel] [PATCH v8 2/7] VMX: Properly handle pi when all the assigned devices are removed

[Feng Wu <feng.wu@xxxxxxxxx>]

This patch handles some corner 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_unblock_vcpu() 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>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v7:
- Prevent the domain from pausing itself.

v6:
- Comments changes
- Rename vmx_pi_list_remove() to vmx_pi_unblock_vcpu()

v5:
- Remove a no-op wrapper

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    | 28 ++++++++++++++++++++++++----
 xen/drivers/passthrough/pci.c | 14 ++++++++++++++
 2 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index f3911f2..a8dcabe 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_unblock_vcpu(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 +196,13 @@ 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_unblock_vcpu(v);
+}
+
 /* This function is called when pcidevs_lock is held */
 void vmx_pi_hooks_assign(struct domain *d)
 {
@@ -215,11 +220,21 @@ 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 not 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_switch_from = NULL;
     d->arch.hvm_domain.vmx.pi_do_resume = NULL;
@@ -230,6 +245,11 @@ void vmx_pi_hooks_deassign(struct domain *d)
      * assigned and "from" hook is NULL. However, it is not straightforward
      * to find a clear solution, so just leave it here.
      */
+
+    for_each_vcpu ( d, v )
+        vmx_pi_unblock_vcpu(v);
+
+    domain_unpause(d);
 }
 
 static int vmx_domain_initialise(struct domain *d)
diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index 8bce213..e71732f 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -1602,6 +1602,13 @@ int iommu_do_pci_domctl(
         break;
 
     case XEN_DOMCTL_assign_device:
+        /* no domain_pause() */
+        if ( d == current->domain )
+        {
+            ret = -EINVAL;
+            break;
+        }
+
         ret = -ENODEV;
         if ( domctl->u.assign_device.dev != XEN_DOMCTL_DEV_PCI )
             break;
@@ -1642,6 +1649,13 @@ int iommu_do_pci_domctl(
         break;
 
     case XEN_DOMCTL_deassign_device:
+        /* no domain_pause() */
+        if ( d == current->domain )
+        {
+            ret = -EINVAL;
+            break;
+        }
+
         ret = -ENODEV;
         if ( domctl->u.assign_device.dev != XEN_DOMCTL_DEV_PCI )
             break;
-- 
2.1.0


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