AMD IOMMU: also allocate IRTEs for HPET MSI

Omitting this was a blatant oversight of mine in commit 2ca9fbd7 ("AMD
IOMMU: allocate IRTE entries instead of using a static mapping").

This also changes a bogus inequality check into a sensible one, even
though it is already known that this will make HPET MSI unusable on
certain systems (having respective broken firmware). This, however,
seems better than failing on systems with consistent ACPI tables.

Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/drivers/passthrough/amd/iommu_intr.c
+++ b/xen/drivers/passthrough/amd/iommu_intr.c
@@ -595,14 +595,31 @@ void* __init amd_iommu_alloc_intremap_ta
 
 int __init amd_setup_hpet_msi(struct msi_desc *msi_desc)
 {
-    if ( (!msi_desc->hpet_id != hpet_sbdf.id) ||
-         (hpet_sbdf.iommu == NULL) )
+    spinlock_t *lock;
+    unsigned long flags;
+    int rc = 0;
+
+    if ( msi_desc->hpet_id != hpet_sbdf.id || !hpet_sbdf.iommu )
     {
-        AMD_IOMMU_DEBUG("Fail to setup HPET MSI remapping\n");
-        return 1;
+        AMD_IOMMU_DEBUG("Failed to setup HPET MSI remapping: %s\n",
+                        hpet_sbdf.iommu ? "Wrong HPET" : "No IOMMU");
+        return -ENODEV;
     }
 
-    return 0;
+    lock = get_intremap_lock(hpet_sbdf.seg, hpet_sbdf.bdf);
+    spin_lock_irqsave(lock, flags);
+
+    msi_desc->remap_index = alloc_intremap_entry(hpet_sbdf.seg,
+                                                 hpet_sbdf.bdf, 1);
+    if ( msi_desc->remap_index >= INTREMAP_ENTRIES )
+    {
+        msi_desc->remap_index = -1;
+        rc = -ENXIO;
+    }
+
+    spin_unlock_irqrestore(lock, flags);
+
+    return rc;
 }
 
 static void dump_intremap_table(const u32 *table)