drm/i915: Do not define vma on stack

Defining vma on stack can cause stack overflow, if
vma gets populated with new fields.

v2:
 (Daniel Vetter)
  - Add kerneldoc for new field

Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210916162819.27848-2-matthew.brost@intel.com

drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c

@@ -413,20 +413,20 @@ static void uc_fw_bind_ggtt(struct intel_uc_fw *uc_fw)
 {
 	struct drm_i915_gem_object *obj = uc_fw->obj;
 	struct i915_ggtt *ggtt = __uc_fw_to_gt(uc_fw)->ggtt;
-	struct i915_vma dummy = {
-		.node.start = uc_fw_ggtt_offset(uc_fw),
-		.node.size = obj->base.size,
-		.pages = obj->mm.pages,
-		.vm = &ggtt->vm,
-	};
+	struct i915_vma *dummy = &uc_fw->dummy;
+
+	dummy->node.start = uc_fw_ggtt_offset(uc_fw);
+	dummy->node.size = obj->base.size;
+	dummy->pages = obj->mm.pages;
+	dummy->vm = &ggtt->vm;
 
 	GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
-	GEM_BUG_ON(dummy.node.size > ggtt->uc_fw.size);
+	GEM_BUG_ON(dummy->node.size > ggtt->uc_fw.size);
 
 	/* uc_fw->obj cache domains were not controlled across suspend */
-	drm_clflush_sg(dummy.pages);
+	drm_clflush_sg(dummy->pages);
 
-	ggtt->vm.insert_entries(&ggtt->vm, &dummy, I915_CACHE_NONE, 0);
+	ggtt->vm.insert_entries(&ggtt->vm, dummy, I915_CACHE_NONE, 0);
 }
 
 static void uc_fw_unbind_ggtt(struct intel_uc_fw *uc_fw)

drivers/gpu/drm/i915/gt/uc/intel_uc_fw.h

@@ -10,6 +10,7 @@
 #include "intel_uc_fw_abi.h"
 #include "intel_device_info.h"
 #include "i915_gem.h"
+#include "i915_vma.h"
 
 struct drm_printer;
 struct drm_i915_private;
@@ -75,6 +76,14 @@ struct intel_uc_fw {
 	bool user_overridden;
 	size_t size;
 	struct drm_i915_gem_object *obj;
+	/**
+	 * @dummy: A vma used in binding the uc fw to ggtt. We can't define this
+	 * vma on the stack as it can lead to a stack overflow, so we define it
+	 * here. Safe to have 1 copy per uc fw because the binding is single
+	 * threaded as it done during driver load (inherently single threaded)
+	 * or during a GT reset (mutex guarantees single threaded).
+	 */
+	struct i915_vma dummy;
 
 	/*
 	 * The firmware build process will generate a version header file with major and