amd/passthrough: Do not leak domain mappings from do_invalidate_dte()

Coverity ID: 1135379

As the code stands, the domain mapping will be leaked on each error path.

The mapping can be for a much shorter period of time, and all the relevent
information can be pulled out at once.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <JBeulich@suse.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>

xen/drivers/passthrough/amd/iommu_guest.c

@@ -424,12 +424,17 @@ static int do_invalidate_dte(struct domain *d, cmd_entry_t *cmd)
                                         sizeof(dev_entry_t), gbdf);
     ASSERT(mfn_valid(dte_mfn));
 
+    /* Read guest dte information */
     dte_base = map_domain_page(dte_mfn);
 
     gdte = dte_base + gbdf % (PAGE_SIZE / sizeof(dev_entry_t));
 
     gdom_id  = get_domid_from_dte(gdte);
     gcr3_gfn = get_guest_cr3_from_dte(gdte);
+    glx      = get_glx_from_dte(gdte);
+    gv       = get_gv_from_dte(gdte);
+
+    unmap_domain_page(dte_base);
 
     /* Do not update host dte before gcr3 has been set */
     if ( gcr3_gfn == 0 )
@@ -440,7 +445,6 @@ static int do_invalidate_dte(struct domain *d, cmd_entry_t *cmd)
 
     ASSERT(mfn_valid(gcr3_mfn));
 
-    /* Read guest dte information */
     iommu = find_iommu_for_device(0, mbdf);
     if ( !iommu )
     {
@@ -449,11 +453,6 @@ static int do_invalidate_dte(struct domain *d, cmd_entry_t *cmd)
         return -ENODEV;
     }
 
-    glx = get_glx_from_dte(gdte);
-    gv = get_gv_from_dte(gdte);
-
-    unmap_domain_page(dte_base);
-
     /* Setup host device entry */
     hdom_id = host_domid(d, gdom_id);
     req_id = get_dma_requestor_id(iommu->seg, mbdf);