On 14/10/2016 16:18, Chris Wilson wrote:
In many places, we try to count pages using a 32 bit integer. That
implies if we are asked to create an object larger than 43bits, we will
subtly crash much later. Catch this on the boundary, and add a warning
to remind ourselves later on our exabyte systems.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
  drivers/gpu/drm/i915/i915_drv.h |  2 +-
  drivers/gpu/drm/i915/i915_gem.c | 14 ++++++++++++--
  2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index fe875b27a6bf..43eb1a72f19e 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3107,7 +3107,7 @@ void i915_gem_object_free(struct drm_i915_gem_object 
  void i915_gem_object_init(struct drm_i915_gem_object *obj,
                         const struct drm_i915_gem_object_ops *ops);
  struct drm_i915_gem_object *i915_gem_object_create(struct drm_device *dev,
-                                                 size_t size);
+                                                  u64 size);
  struct drm_i915_gem_object *i915_gem_object_create_from_data(
                struct drm_device *dev, const void *data, size_t size);
  void i915_gem_close_object(struct drm_gem_object *gem, struct drm_file *file);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index fe92e28ea0a8..0d1dc04302ec 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4131,14 +4131,24 @@ static const struct drm_i915_gem_object_ops 
i915_gem_object_ops = {
        .put_pages = i915_gem_object_put_pages_gtt,
-struct drm_i915_gem_object *i915_gem_object_create(struct drm_device *dev,
-                                                 size_t size)
+struct drm_i915_gem_object *
+i915_gem_object_create(struct drm_device *dev, u64 size)
        struct drm_i915_gem_object *obj;
        struct address_space *mapping;
        gfp_t mask;
        int ret;
+ /* There is a prevalence of the assumption that we fit the object's
+        * page count inside a 32bit variable. Let's document this and catch
+        * if we ever need to fix it.
+        */
+       if (WARN_ON(size >> PAGE_SHIFT > INT_MAX))
+               return ERR_PTR(-E2BIG);
+       if (sizeof(size_t) < sizeof(u64) && size > INT_MAX)
+               return ERR_PTR(-E2BIG);

Shouldn't it be UINT_MAX in both cases?

We could try to future proof more maybe like sizeof(typeof(obj->base.size)), is typeof can be used like that? Something similar for sg API if possible. But then again, it could be better future proofing to be hardcoded like you wrote it. Yes I think so.



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