drm/i915: Don't prefault the entire obj if the vma is smaller

Take the minimum of the object size and the vma size and prefault
only that much. Avoids a SIGBUS when mmapping only a portion of the
object.

Prefaulting was introduced here:
 commit b90b91d87038f6b257b40a02b42ed4f9705e06f0
 Author: Chris Wilson <[email protected]>
 Date:   Tue Jun 10 12:14:40 2014 +0100

    drm/i915: Prefault the entire object on first page fault

Cc: Chris Wilson <[email protected]>
Signed-off-by: Ville Syrjälä <[email protected]>
Testcase: igt/gem_mmap/short-mmap
Signed-off-by: Daniel Vetter <[email protected]>

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 7f643db268295048f5efd480b89ef708891f84eb..d8364135c2e557771b269e0edd05a3220c16d8f0 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1570,9 +1570,12 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
        pfn >>= PAGE_SHIFT;
 
        if (!obj->fault_mappable) {
+               unsigned long size = min_t(unsigned long,
+                                          vma->vm_end - vma->vm_start,
+                                          obj->base.size);
                int i;
 
-               for (i = 0; i < obj->base.size >> PAGE_SHIFT; i++) {
+               for (i = 0; i < size >> PAGE_SHIFT; i++) {
                        ret = vm_insert_pfn(vma,
                                            (unsigned long)vma->vm_start + i * PAGE_SIZE,
                                            pfn + i);