passthrough: don't migrate pirq when it is delivered through VT-d PI

When a vCPU was migrated to another pCPU, pt irqs binded to this vCPU might
also need migration as a optimization to reduce IPI between pCPUs. When VT-d
PI is enabled, interrupt vector will be recorded to a main memory resident
data-structure and a notification whose destination is decided by NDST is
generated. NDST is properly adjusted during vCPU migration so pirq directly
injected to guest needn't be migrated.

This patch adds a indicator, @posted, to show whether the pt irq is delivered
through VT-d PI. Also this patch fixes a bug that hvm_migrate_pirq() accesses
pirq_dpci->gmsi.dest_vcpu_id without checking the pirq_dpci's type.

Signed-off-by: Chao Gao <chao.gao@intel.com>
[jb: remove an extranious check from hvm_migrate_pirq()]
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/hvm.c

@@ -438,6 +438,8 @@ static int hvm_migrate_pirq(struct domain *d, struct hvm_pirq_dpci *pirq_dpci,
     struct vcpu *v = arg;
 
     if ( (pirq_dpci->flags & HVM_IRQ_DPCI_MACH_MSI) &&
+         /* Needn't migrate pirq if this pirq is delivered to guest directly.*/
+         !pirq_dpci->gmsi.posted &&
          (pirq_dpci->gmsi.dest_vcpu_id == v->vcpu_id) )
     {
         struct irq_desc *desc =

xen/drivers/passthrough/io.c

@@ -259,52 +259,6 @@ static struct vcpu *vector_hashing_dest(const struct domain *d,
     return dest;
 }
 
-/*
- * The purpose of this routine is to find the right destination vCPU for
- * an interrupt which will be delivered by VT-d posted-interrupt. There
- * are several cases as below:
- *
- * - For lowest-priority interrupts, use vector-hashing mechanism to find
- *   the destination.
- * - Otherwise, for single destination interrupt, it is straightforward to
- *   find the destination vCPU and return true.
- * - For multicast/broadcast vCPU, we cannot handle it via interrupt posting,
- *   so return NULL.
- */
-static struct vcpu *pi_find_dest_vcpu(const struct domain *d, uint32_t dest_id,
-                                      bool_t dest_mode, uint8_t delivery_mode,
-                                      uint8_t gvec)
-{
-    unsigned int dest_vcpus = 0;
-    struct vcpu *v, *dest = NULL;
-
-    switch ( delivery_mode )
-    {
-    case dest_LowestPrio:
-        return vector_hashing_dest(d, dest_id, dest_mode, gvec);
-    case dest_Fixed:
-        for_each_vcpu ( d, v )
-        {
-            if ( !vlapic_match_dest(vcpu_vlapic(v), NULL, APIC_DEST_NOSHORT,
-                                    dest_id, dest_mode) )
-                continue;
-
-            dest_vcpus++;
-            dest = v;
-        }
-
-        /* For fixed mode, we only handle single-destination interrupts. */
-        if ( dest_vcpus == 1 )
-            return dest;
-
-        break;
-    default:
-        break;
-    }
-
-    return NULL;
-}
-
 int pt_irq_create_bind(
     struct domain *d, xen_domctl_bind_pt_irq_t *pt_irq_bind)
 {
@@ -365,6 +319,7 @@ int pt_irq_create_bind(
     {
         uint8_t dest, dest_mode, delivery_mode;
         int dest_vcpu_id;
+        const struct vcpu *vcpu;
 
         if ( !(pirq_dpci->flags & HVM_IRQ_DPCI_MAPPED) )
         {
@@ -442,17 +397,25 @@ int pt_irq_create_bind(
         dest_vcpu_id = hvm_girq_dest_2_vcpu_id(d, dest, dest_mode);
         pirq_dpci->gmsi.dest_vcpu_id = dest_vcpu_id;
         spin_unlock(&d->event_lock);
+
+        pirq_dpci->gmsi.posted = false;
+        vcpu = (dest_vcpu_id >= 0) ? d->vcpu[dest_vcpu_id] : NULL;
+        if ( iommu_intpost )
+        {
+            if ( delivery_mode == dest_LowestPrio )
+                vcpu = vector_hashing_dest(d, dest, dest_mode,
+                                           pirq_dpci->gmsi.gvec);
+            if ( vcpu )
+                pirq_dpci->gmsi.posted = true;
+        }
         if ( dest_vcpu_id >= 0 )
             hvm_migrate_pirqs(d->vcpu[dest_vcpu_id]);
 
         /* Use interrupt posting if it is supported. */
         if ( iommu_intpost )
         {
-            const struct vcpu *vcpu = pi_find_dest_vcpu(d, dest, dest_mode,
-                                          delivery_mode, pirq_dpci->gmsi.gvec);
-
             if ( vcpu )
-                pi_update_irte( vcpu, info, pirq_dpci->gmsi.gvec );
+                pi_update_irte(vcpu, info, pirq_dpci->gmsi.gvec);
             else
                 dprintk(XENLOG_G_INFO,
                         "%pv: deliver interrupt in remapping mode,gvec:%02x\n",

xen/include/xen/hvm/irq.h

@@ -63,6 +63,7 @@ struct hvm_gmsi_info {
     uint32_t gvec;
     uint32_t gflags;
     int dest_vcpu_id; /* -1 :multi-dest, non-negative: dest_vcpu_id */
+    bool posted; /* directly deliver to guest via VT-d PI? */
 };
 
 struct hvm_girq_dpci_mapping {