drm/amdgpu: user pages array memory leak fix

user_pages array should always be freed after validation regardless if
user pages are changed after bo is created because with HMM change parse
bo always allocate user pages array to get user pages for userptr bo.

v2: remove unused local variable and amend commit

v3: add back get user pages in gem_userptr_ioctl, to detect application
bug where an userptr VMA is not ananymous memory and reject it.

Bugzilla: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1844962

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Tested-by: Joe Barnett <thejoe@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org # 5.3

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c

@@ -536,7 +536,6 @@ static int amdgpu_cs_list_validate(struct amdgpu_cs_parser *p,
 
 	list_for_each_entry(lobj, validated, tv.head) {
 		struct amdgpu_bo *bo = ttm_to_amdgpu_bo(lobj->tv.bo);
-		bool binding_userptr = false;
 		struct mm_struct *usermm;
 
 		usermm = amdgpu_ttm_tt_get_usermm(bo->tbo.ttm);
@@ -553,7 +552,6 @@ static int amdgpu_cs_list_validate(struct amdgpu_cs_parser *p,
 
 			amdgpu_ttm_tt_set_user_pages(bo->tbo.ttm,
 						     lobj->user_pages);
-			binding_userptr = true;
 		}
 
 		if (p->evictable == lobj)
@@ -563,10 +561,8 @@ static int amdgpu_cs_list_validate(struct amdgpu_cs_parser *p,
 		if (r)
 			return r;
 
-		if (binding_userptr) {
-			kvfree(lobj->user_pages);
-			lobj->user_pages = NULL;
-		}
+		kvfree(lobj->user_pages);
+		lobj->user_pages = NULL;
 	}
 	return 0;
 }