[PATCH 2/3] drm/i915: Refactor relocs ptr pre-fault

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Remove the reliance on relocs_max handling the limitation of
fault_in_pages_readable and also remove the data type mismatch.

This will allow the refactoring of relocation_count and
relocs_total range checking in the following patch.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index ee269de7d778..a5e748d226f6 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -1192,7 +1192,7 @@ validate_exec_list(struct drm_device *dev,
 
 	for (i = 0; i < count; i++) {
 		char __user *ptr = u64_to_user_ptr(exec[i].relocs_ptr);
-		int length; /* limited by fault_in_pages_readable() */
+		u64 length;
 
 		if (exec[i].flags & invalid_flags)
 			return -EINVAL;
@@ -1232,18 +1232,29 @@ validate_exec_list(struct drm_device *dev,
 		relocs_total += exec[i].relocation_count;
 
 		length = exec[i].relocation_count *
-			sizeof(struct drm_i915_gem_relocation_entry);
+			 sizeof(struct drm_i915_gem_relocation_entry);
+
 		/*
 		 * We must check that the entire relocation array is safe
 		 * to read, but since we may need to update the presumed
 		 * offsets during execution, check for full write access.
+		 *
+		 * Do it in INT_MAX sized chunks to account for the limitation
+		 * of fault_in_pages_readable.
 		 */
-		if (!access_ok(VERIFY_WRITE, ptr, length))
-			return -EFAULT;
+		while (length) {
+			int size = min_t(u64, length, INT_MAX);
 
-		if (likely(!i915.prefault_disable)) {
-			if (fault_in_pages_readable(ptr, length))
+			if (!access_ok(VERIFY_WRITE, ptr, size))
 				return -EFAULT;
+
+			if (likely(!i915.prefault_disable)) {
+				if (fault_in_pages_readable(ptr, size))
+					return -EFAULT;
+			}
+
+			ptr += size;
+			length -= size;
 		}
 	}
 
-- 
2.9.4