[PATCH 4/6] drm/i915: Fix lock order reversal in shmem pread path.

[Eric Anholt <eric@anholt.net>]

Signed-off-by: Eric Anholt <eric@anholt.net>
---
 drivers/gpu/drm/i915/i915_gem.c |  221 ++++++++++++++++++++++++++++++++++-----
 1 files changed, 195 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index bdc7326..010af90 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -137,6 +137,24 @@ i915_gem_create_ioctl(struct drm_device *dev, void *data,
 }
 
 static inline int
+fast_shmem_read(struct page **pages,
+		loff_t page_base, int page_offset,
+		char __user *data,
+		int length)
+{
+	char __iomem *vaddr;
+	int ret;
+
+	vaddr = kmap_atomic(pages[page_base >> PAGE_SHIFT], KM_USER0);
+	if (vaddr == NULL)
+		return -ENOMEM;
+	ret = __copy_to_user_inatomic(data, vaddr + page_offset, length);
+	kunmap_atomic(vaddr, KM_USER0);
+
+	return ret;
+}
+
+static inline int
 slow_shmem_copy(struct page *dst_page,
 		int dst_offset,
 		struct page *src_page,
@@ -164,6 +182,179 @@ slow_shmem_copy(struct page *dst_page,
 }
 
 /**
+ * This is the fast shmem pread path, which attempts to copy_from_user directly
+ * from the backing pages of the object to the user's address space.  On a
+ * fault, it fails so we can fall back to i915_gem_shmem_pwrite_slow().
+ */
+static int
+i915_gem_shmem_pread_fast(struct drm_device *dev, struct drm_gem_object *obj,
+			  struct drm_i915_gem_pread *args,
+			  struct drm_file *file_priv)
+{
+	struct drm_i915_gem_object *obj_priv = obj->driver_private;
+	ssize_t remain;
+	loff_t offset, page_base;
+	char __user *user_data;
+	int page_offset, page_length;
+	int ret;
+
+	user_data = (char __user *) (uintptr_t) args->data_ptr;
+	remain = args->size;
+
+	mutex_lock(&dev->struct_mutex);
+
+	ret = i915_gem_object_get_pages(obj);
+	if (ret != 0)
+		goto fail_unlock;
+
+	ret = i915_gem_object_set_cpu_read_domain_range(obj, args->offset,
+							args->size);
+	if (ret != 0)
+		goto fail_put_pages;
+
+	obj_priv = obj->driver_private;
+	offset = args->offset;
+
+	while (remain > 0) {
+		/* Operation in this page
+		 *
+		 * page_base = page offset within aperture
+		 * page_offset = offset within page
+		 * page_length = bytes to copy for this page
+		 */
+		page_base = (offset & ~(PAGE_SIZE-1));
+		page_offset = offset & (PAGE_SIZE-1);
+		page_length = remain;
+		if ((page_offset + remain) > PAGE_SIZE)
+			page_length = PAGE_SIZE - page_offset;
+
+		ret = fast_shmem_read(obj_priv->pages,
+				      page_base, page_offset,
+				      user_data, page_length);
+		if (ret)
+			goto fail_put_pages;
+
+		remain -= page_length;
+		user_data += page_length;
+		offset += page_length;
+	}
+
+fail_put_pages:
+	i915_gem_object_put_pages(obj);
+fail_unlock:
+	mutex_unlock(&dev->struct_mutex);
+
+	return ret;
+}
+
+/**
+ * This is the fallback shmem pread path, which allocates temporary storage
+ * in kernel space to copy_to_user into outside of the struct_mutex, so we
+ * can copy out of the object's backing pages while holding the struct mutex
+ * and not take page faults.
+ */
+static int
+i915_gem_shmem_pread_slow(struct drm_device *dev, struct drm_gem_object *obj,
+			  struct drm_i915_gem_pread *args,
+			  struct drm_file *file_priv)
+{
+	struct drm_i915_gem_object *obj_priv = obj->driver_private;
+	struct mm_struct *mm = current->mm;
+	struct page **user_pages;
+	ssize_t remain;
+	loff_t offset, pinned_pages, i;
+	loff_t first_data_page, last_data_page, num_pages;
+	int shmem_page_index, shmem_page_offset;
+	int data_page_index,  data_page_offset;
+	int page_length;
+	int ret;
+	uint64_t data_ptr = args->data_ptr;
+
+	remain = args->size;
+
+	/* Pin the user pages containing the data.  We can't fault while
+	 * holding the struct mutex, yet we want to hold it while
+	 * dereferencing the user data.
+	 */
+	first_data_page = data_ptr / PAGE_SIZE;
+	last_data_page = (data_ptr + args->size - 1) / PAGE_SIZE;
+	num_pages = last_data_page - first_data_page + 1;
+
+	user_pages = kcalloc(num_pages, sizeof(struct page *), GFP_KERNEL);
+	if (user_pages == NULL)
+		return -ENOMEM;
+
+	down_read(&mm->mmap_sem);
+	pinned_pages = get_user_pages(current, mm, (uintptr_t)args->data_ptr,
+				      num_pages, 0, 0, user_pages, NULL);
+	up_read(&mm->mmap_sem);
+	if (pinned_pages < num_pages) {
+		ret = -EFAULT;
+		goto fail_put_user_pages;
+	}
+
+	mutex_lock(&dev->struct_mutex);
+
+	ret = i915_gem_object_get_pages(obj);
+	if (ret != 0)
+		goto fail_unlock;
+
+	ret = i915_gem_object_set_cpu_read_domain_range(obj, args->offset,
+							args->size);
+	if (ret != 0)
+		goto fail_put_pages;
+
+	obj_priv = obj->driver_private;
+	offset = args->offset;
+
+	while (remain > 0) {
+		/* Operation in this page
+		 *
+		 * shmem_page_index = page number within shmem file
+		 * shmem_page_offset = offset within page in shmem file
+		 * data_page_index = page number in get_user_pages return
+		 * data_page_offset = offset with data_page_index page.
+		 * page_length = bytes to copy for this page
+		 */
+		shmem_page_index = offset / PAGE_SIZE;
+		shmem_page_offset = offset & ~PAGE_MASK;
+		data_page_index = data_ptr / PAGE_SIZE - first_data_page;
+		data_page_offset = data_ptr & ~PAGE_MASK;
+
+		page_length = remain;
+		if ((shmem_page_offset + page_length) > PAGE_SIZE)
+			page_length = PAGE_SIZE - shmem_page_offset;
+		if ((data_page_offset + page_length) > PAGE_SIZE)
+			page_length = PAGE_SIZE - data_page_offset;
+
+		ret = slow_shmem_copy(user_pages[data_page_index],
+				      data_page_offset,
+				      obj_priv->pages[shmem_page_index],
+				      shmem_page_offset,
+				      page_length);
+		if (ret)
+			goto fail_put_pages;
+
+		remain -= page_length;
+		data_ptr += page_length;
+		offset += page_length;
+	}
+
+fail_put_pages:
+	i915_gem_object_put_pages(obj);
+fail_unlock:
+	mutex_unlock(&dev->struct_mutex);
+fail_put_user_pages:
+	for (i = 0; i < pinned_pages; i++) {
+		SetPageDirty(user_pages[i]);
+		page_cache_release(user_pages[i]);
+	}
+	kfree(user_pages);
+
+	return ret;
+}
+
+/**
  * Reads data from the object referenced by handle.
  *
  * On error, the contents of *data are undefined.
@@ -175,8 +366,6 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
 	struct drm_i915_gem_pread *args = data;
 	struct drm_gem_object *obj;
 	struct drm_i915_gem_object *obj_priv;
-	ssize_t read;
-	loff_t offset;
 	int ret;
 
 	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
@@ -194,33 +383,13 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
 		return -EINVAL;
 	}
 
-	mutex_lock(&dev->struct_mutex);
-
-	ret = i915_gem_object_set_cpu_read_domain_range(obj, args->offset,
-							args->size);
-	if (ret != 0) {
-		drm_gem_object_unreference(obj);
-		mutex_unlock(&dev->struct_mutex);
-		return ret;
-	}
-
-	offset = args->offset;
-
-	read = vfs_read(obj->filp, (char __user *)(uintptr_t)args->data_ptr,
-			args->size, &offset);
-	if (read != args->size) {
-		drm_gem_object_unreference(obj);
-		mutex_unlock(&dev->struct_mutex);
-		if (read < 0)
-			return read;
-		else
-			return -EINVAL;
-	}
+	ret = i915_gem_shmem_pread_fast(dev, obj, args, file_priv);
+	if (ret != 0)
+		ret = i915_gem_shmem_pread_slow(dev, obj, args, file_priv);
 
 	drm_gem_object_unreference(obj);
-	mutex_unlock(&dev->struct_mutex);
 
-	return 0;
+	return ret;
 }
 
 /* This is the fast write path which cannot handle
-- 
1.6.2.1