AMD IOMMU: handle MSI for phantom functions

With ordinary requests allowed to come from phantom functions, the
remapping tables ought to be set up to also allow for MSI triggers to
come from other than the "real" device too.

It is not clear to me whether the alias-ID handling also needs
adjustment for this to work properly, or whether firmware can be
expected to properly express this through a device alias range
descriptor (or multiple device alias ones).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/drivers/passthrough/amd/iommu_intr.c
+++ b/xen/drivers/passthrough/amd/iommu_intr.c
@@ -286,7 +286,7 @@ void amd_iommu_ioapic_update_ire(
 
 static void update_intremap_entry_from_msi_msg(
     struct amd_iommu *iommu, u16 bdf,
-    struct msi_desc *msi_desc, struct msi_msg *msg)
+    int *remap_index, const struct msi_msg *msg)
 {
     unsigned long flags;
     u32* entry;
@@ -302,7 +302,7 @@ static void update_intremap_entry_from_m
     {
         lock = get_intremap_lock(iommu->seg, req_id);
         spin_lock_irqsave(lock, flags);
-        free_intremap_entry(iommu->seg, req_id, msi_desc->remap_index);
+        free_intremap_entry(iommu->seg, req_id, *remap_index);
         spin_unlock_irqrestore(lock, flags);
 
         if ( ( req_id != alias_id ) &&
@@ -310,7 +310,7 @@ static void update_intremap_entry_from_m
         {
             lock = get_intremap_lock(iommu->seg, alias_id);
             spin_lock_irqsave(lock, flags);
-            free_intremap_entry(iommu->seg, alias_id, msi_desc->remap_index);
+            free_intremap_entry(iommu->seg, alias_id, *remap_index);
             spin_unlock_irqrestore(lock, flags);
         }
         goto done;
@@ -324,7 +324,10 @@ static void update_intremap_entry_from_m
     vector = (msg->data >> MSI_DATA_VECTOR_SHIFT) & MSI_DATA_VECTOR_MASK;
     dest = (msg->address_lo >> MSI_ADDR_DEST_ID_SHIFT) & 0xff;
     offset = get_intremap_offset(vector, delivery_mode);
-    msi_desc->remap_index = offset;
+    if ( *remap_index < 0)
+        *remap_index = offset;
+    else
+        BUG_ON(*remap_index != offset);
 
     entry = (u32*)get_intremap_entry(iommu->seg, req_id, offset);
     update_intremap_entry(entry, vector, delivery_mode, dest_mode, dest);
@@ -379,12 +382,30 @@ void amd_iommu_msi_msg_update_ire(
     }
 
     if ( msi_desc->remap_index >= 0 )
-        update_intremap_entry_from_msi_msg(iommu, bdf, msi_desc, NULL);
+    {
+        do {
+            update_intremap_entry_from_msi_msg(iommu, bdf,
+                                               &msi_desc->remap_index, NULL);
+            if ( !pdev || !pdev->phantom_stride )
+                break;
+            bdf += pdev->phantom_stride;
+        } while ( PCI_SLOT(bdf) == PCI_SLOT(pdev->devfn) );
+
+        msi_desc->remap_index = -1;
+        if ( pdev )
+            bdf = PCI_BDF2(pdev->bus, pdev->devfn);
+    }
 
     if ( !msg )
         return;
 
-    update_intremap_entry_from_msi_msg(iommu, bdf, msi_desc, msg);
+    do {
+        update_intremap_entry_from_msi_msg(iommu, bdf, &msi_desc->remap_index,
+                                           msg);
+        if ( !pdev || !pdev->phantom_stride )
+            break;
+        bdf += pdev->phantom_stride;
+    } while ( PCI_SLOT(bdf) == PCI_SLOT(pdev->devfn) );
 }
 
 void amd_iommu_read_msi_from_ire(