intel_iommu: refine iotlb hash calculation

Commit 1b2b12376c8 ("intel-iommu: PASID support") takes PASID into
account when calculating iotlb hash like:

static guint vtd_iotlb_hash(gconstpointer v)
{
    const struct vtd_iotlb_key *key = v;

    return key->gfn | ((key->sid) << VTD_IOTLB_SID_SHIFT) |
           (key->level) << VTD_IOTLB_LVL_SHIFT |
           (key->pasid) << VTD_IOTLB_PASID_SHIFT;
}

This turns out to be problematic since:

- the shift will lose bits if not converting to uint64_t
- level should be off by one in order to fit into 2 bits
- VTD_IOTLB_PASID_SHIFT is 30 but PASID is 20 bits which will waste
  some bits
- the hash result is uint64_t so we will lose bits when converting to
  guint

So this patch fixes them by

- converting the keys into uint64_t before doing the shift
- off level by one to make it fit into two bits
- change the sid, lvl and pasid shift to 26, 42 and 44 in order to
  take the full width of uint64_t
- perform an XOR to the top 32bit with the bottom 32bit for the final
  result to fit guint

Fixes: Coverity CID 1508100
Fixes: 1b2b12376c8 ("intel-iommu: PASID support")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230412073510.7158-1-jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>

hw/i386/intel_iommu.c

@@ -64,8 +64,8 @@ struct vtd_as_key {
 struct vtd_iotlb_key {
     uint64_t gfn;
     uint32_t pasid;
-    uint32_t level;
     uint16_t sid;
+    uint8_t level;
 };
 
 static void vtd_address_space_refresh_all(IntelIOMMUState *s);
@@ -221,10 +221,11 @@ static gboolean vtd_iotlb_equal(gconstpointer v1, gconstpointer v2)
 static guint vtd_iotlb_hash(gconstpointer v)
 {
     const struct vtd_iotlb_key *key = v;
+    uint64_t hash64 = key->gfn | ((uint64_t)(key->sid) << VTD_IOTLB_SID_SHIFT) |
+        (uint64_t)(key->level - 1) << VTD_IOTLB_LVL_SHIFT |
+        (uint64_t)(key->pasid) << VTD_IOTLB_PASID_SHIFT;
 
-    return key->gfn | ((key->sid) << VTD_IOTLB_SID_SHIFT) |
-           (key->level) << VTD_IOTLB_LVL_SHIFT |
-           (key->pasid) << VTD_IOTLB_PASID_SHIFT;
+    return (guint)((hash64 >> 32) ^ (hash64 & 0xffffffffU));
 }
 
 static gboolean vtd_as_equal(gconstpointer v1, gconstpointer v2)

hw/i386/intel_iommu_internal.h

@@ -114,9 +114,9 @@
                                      VTD_INTERRUPT_ADDR_FIRST + 1)
 
 /* The shift of source_id in the key of IOTLB hash table */
-#define VTD_IOTLB_SID_SHIFT         20
-#define VTD_IOTLB_LVL_SHIFT         28
-#define VTD_IOTLB_PASID_SHIFT       30
+#define VTD_IOTLB_SID_SHIFT         26
+#define VTD_IOTLB_LVL_SHIFT         42
+#define VTD_IOTLB_PASID_SHIFT       44
 #define VTD_IOTLB_MAX_SIZE          1024    /* Max size of the hash table */
 
 /* IOTLB_REG */