CA-236863: division by 0 in VGPU-g detection (xapi-project#281)

* CA-236863: division by 0 in VGPU-g detection

If the Intel GPU BAR size is too small, the number of VGPUs per PGPU
could become zero and give rise to a division by zero.  The suggested
fix adds an itermediate check to the VGPU generation code to prevent
this from happening.

Signed-off-by: Marcello Seri <[email protected]>

* CA-236863: add warning in the logs if BAR size is too small

Signed-off-by: Marcello Seri <[email protected]>

* Cleanup vgpu_type record creation

Signed-off-by: Marcello Seri <[email protected]>

Author: mseri

ocaml/xapi/xapi_vgpu_type.ml

@@ -467,36 +467,55 @@ module Intel = struct
       List.nth device.Pci.Pci_dev.size 2
       |> Int64.of_nativeint
     in
-    List.map
+    let rec collect acc = function
+      | []             -> acc
+      | Some v :: tail -> collect (v :: acc) tail
+      | None   :: tail -> collect acc tail
+    in
+    whitelist
+    |> List.map
       Identifier.(fun conf ->
           let vgpus_per_pgpu =
             bar_size /// 1024L /// 1024L
             /// conf.identifier.low_gm_sz
             --- 1L
           in
-          let vgpu_size = Constants.pgpu_default_size /// vgpus_per_pgpu in
-          {
-            vendor_name;
-            model_name = conf.model_name;
-            framebuffer_size = conf.framebufferlength;
-            max_heads = conf.num_heads;
-            max_resolution_x = conf.max_x;
-            max_resolution_y = conf.max_y;
-            size = vgpu_size;
-            internal_config = [
-              Xapi_globs.vgt_low_gm_sz, Int64.to_string conf.identifier.low_gm_sz;
-              Xapi_globs.vgt_high_gm_sz, Int64.to_string conf.identifier.high_gm_sz;
-              Xapi_globs.vgt_fence_sz, Int64.to_string conf.identifier.fence_sz;
-            ] @ (
-                match conf.identifier.monitor_config_file with
+          if vgpus_per_pgpu <= 0L then 
+            begin
+              warn "Not enough memory for Intel VGPUs. \
+                    If you intend to use them, increase the GPU \
+                    BAR size in the BIOS settings.";
+              None
+            end
+          else
+            let vgpu_size =
+              Constants.pgpu_default_size /// vgpus_per_pgpu
+            in
+            let internal_config = let open Xapi_globs in
+              List.concat [
+                [ vgt_low_gm_sz, Int64.to_string conf.identifier.low_gm_sz
+                ; vgt_high_gm_sz, Int64.to_string conf.identifier.high_gm_sz
+                ; vgt_fence_sz, Int64.to_string conf.identifier.fence_sz
+                ]
+              ; match conf.identifier.monitor_config_file with
                 | Some monitor_config_file ->
-                  [Xapi_globs.vgt_monitor_config_file, monitor_config_file]
+                  [vgt_monitor_config_file, monitor_config_file]
                 | None -> []
-              );
-            identifier = GVT_g conf.identifier;
-            experimental = conf.experimental;
-          })
-      whitelist
+              ]
+            in
+            Some {
+              vendor_name;
+              model_name = conf.model_name;
+              framebuffer_size = conf.framebufferlength;
+              max_heads = conf.num_heads;
+              max_resolution_x = conf.max_x;
+              max_resolution_y = conf.max_y;
+              size = vgpu_size;
+              internal_config = internal_config;
+              identifier = GVT_g conf.identifier;
+              experimental = conf.experimental;
+            })
+    |> collect []
 
   let find_or_create_supported_types ~__context ~pci
       ~is_system_display_device