drm/i915/userptr: fix size calculation

If we create a rather large userptr object(e.g 1ULL << 32) we might
shift past the type-width of num_pages: (int)num_pages << PAGE_SHIFT,
resulting in a totally bogus sg_table, which fortunately will eventually
manifest as:

gen8_ppgtt_insert_huge:463 GEM_BUG_ON(iter->sg->length < page_size)
kernel BUG at drivers/gpu/drm/i915/gt/gen8_ppgtt.c:463!

v2: more unsigned long
    prefer I915_GTT_PAGE_SIZE

Fixes: 5cc9ed4b ("drm/i915: Introduce mapping of user pages into video memory (userptr) ioctl")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200117132413.1170563-2-matthew.auld@intel.com

drivers/gpu/drm/i915/gem/i915_gem_userptr.c

@@ -403,7 +403,7 @@ struct get_pages_work {
 
 static struct sg_table *
 __i915_gem_userptr_alloc_pages(struct drm_i915_gem_object *obj,
-			       struct page **pvec, int num_pages)
+			       struct page **pvec, unsigned long num_pages)
 {
 	unsigned int max_segment = i915_sg_segment_size();
 	struct sg_table *st;
@@ -449,9 +449,10 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
 {
 	struct get_pages_work *work = container_of(_work, typeof(*work), work);
 	struct drm_i915_gem_object *obj = work->obj;
-	const int npages = obj->base.size >> PAGE_SHIFT;
+	const unsigned long npages = obj->base.size >> PAGE_SHIFT;
+	unsigned long pinned;
 	struct page **pvec;
-	int pinned, ret;
+	int ret;
 
 	ret = -ENOMEM;
 	pinned = 0;
@@ -559,7 +560,7 @@ __i915_gem_userptr_get_pages_schedule(struct drm_i915_gem_object *obj)
 
 static int i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
 {
-	const int num_pages = obj->base.size >> PAGE_SHIFT;
+	const unsigned long num_pages = obj->base.size >> PAGE_SHIFT;
 	struct mm_struct *mm = obj->userptr.mm->mm;
 	struct page **pvec;
 	struct sg_table *pages;

drivers/gpu/drm/i915/gt/gen6_ppgtt.c

@@ -131,6 +131,7 @@ static void gen6_ppgtt_insert_entries(struct i915_address_space *vm,
 
 	vaddr = kmap_atomic_px(i915_pt_entry(pd, act_pt));
 	do {
+		GEM_BUG_ON(iter.sg->length < I915_GTT_PAGE_SIZE);
 		vaddr[act_pte] = pte_encode | GEN6_PTE_ADDR_ENCODE(iter.dma);
 
 		iter.dma += I915_GTT_PAGE_SIZE;

drivers/gpu/drm/i915/gt/gen8_ppgtt.c

@@ -379,6 +379,7 @@ gen8_ppgtt_insert_pte(struct i915_ppgtt *ppgtt,
 	pd = i915_pd_entry(pdp, gen8_pd_index(idx, 2));
 	vaddr = kmap_atomic_px(i915_pt_entry(pd, gen8_pd_index(idx, 1)));
 	do {
+		GEM_BUG_ON(iter->sg->length < I915_GTT_PAGE_SIZE);
 		vaddr[gen8_pd_index(idx, 0)] = pte_encode | iter->dma;
 
 		iter->dma += I915_GTT_PAGE_SIZE;