intel_iommu: Use correct shift for 256 bits qi descriptor

In chapter 10.4.23 of VT-d spec 3.0, Descriptor Width bit was introduced
in VTD_IQA_REG. Software could set this bit to tell VT-d the QI descriptor
from software would be 256 bits. Accordingly, the VTD_IQH_QH_SHIFT should
be 5 when descriptor size is 256 bits.

This patch adds the DW bit check when deciding the shift used to update
VTD_IQH_REG.

Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
Message-Id: <1593850035-35483-1-git-send-email-yi.l.liu@intel.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit a4544c45e1)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/i386/intel_iommu.c

@@ -2549,6 +2549,11 @@ static bool vtd_process_inv_desc(IntelIOMMUState *s)
 /* Try to fetch and process more Invalidation Descriptors */
 static void vtd_fetch_inv_desc(IntelIOMMUState *s)
 {
+    int qi_shift;
+
+    /* Refer to 10.4.23 of VT-d spec 3.0 */
+    qi_shift = s->iq_dw ? VTD_IQH_QH_SHIFT_5 : VTD_IQH_QH_SHIFT_4;
+
     trace_vtd_inv_qi_fetch();
 
     if (s->iq_tail >= s->iq_size) {
@@ -2567,7 +2572,7 @@ static void vtd_fetch_inv_desc(IntelIOMMUState *s)
         }
         /* Must update the IQH_REG in time */
         vtd_set_quad_raw(s, DMAR_IQH_REG,
-                         (((uint64_t)(s->iq_head)) << VTD_IQH_QH_SHIFT) &
+                         (((uint64_t)(s->iq_head)) << qi_shift) &
                          VTD_IQH_QH_MASK);
     }
 }

hw/i386/intel_iommu_internal.h

@@ -230,7 +230,8 @@
 #define VTD_IQA_DW_MASK             0x800
 
 /* IQH_REG */
-#define VTD_IQH_QH_SHIFT            4
+#define VTD_IQH_QH_SHIFT_4          4
+#define VTD_IQH_QH_SHIFT_5          5
 #define VTD_IQH_QH_MASK             0x7fff0ULL
 
 /* ICS_REG */