drm/i915: Fix lock order reversal in GTT pwrite path.

Since the pagefault path determines that the lock order we use has to be
mmap_sem -> struct_mutex, we can't allow page faults to occur while the
struct_mutex is held.  To fix this in pwrite, we first try optimistically to
see if we can copy from user without faulting.  If it fails, fall back to
using get_user_pages to pin the user's memory, and map those pages
atomically when copying it to the GPU.

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 37427e4..35f8c7b 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -223,29 +223,34 @@ fast_user_write(struct io_mapping *mapping,
  */
 
 static inline int
-slow_user_write(struct io_mapping *mapping,
-               loff_t page_base, int page_offset,
-               char __user *user_data,
-               int length)
+slow_kernel_write(struct io_mapping *mapping,
+                 loff_t gtt_base, int gtt_offset,
+                 struct page *user_page, int user_offset,
+                 int length)
 {
-       char __iomem *vaddr;
+       char *src_vaddr, *dst_vaddr;
        unsigned long unwritten;
 
-       vaddr = io_mapping_map_wc(mapping, page_base);
-       if (vaddr == NULL)
-               return -EFAULT;
-       unwritten = __copy_from_user(vaddr + page_offset,
-                                    user_data, length);
-       io_mapping_unmap(vaddr);
+       dst_vaddr = io_mapping_map_atomic_wc(mapping, gtt_base);
+       src_vaddr = kmap_atomic(user_page, KM_USER1);
+       unwritten = __copy_from_user_inatomic_nocache(dst_vaddr + gtt_offset,
+                                                     src_vaddr + user_offset,
+                                                     length);
+       kunmap_atomic(src_vaddr, KM_USER1);
+       io_mapping_unmap_atomic(dst_vaddr);
        if (unwritten)
                return -EFAULT;
        return 0;
 }
 
+/**
+ * This is the fast pwrite path, where we copy the data directly from the
+ * user into the GTT, uncached.
+ */
 static int
-i915_gem_gtt_pwrite(struct drm_device *dev, struct drm_gem_object *obj,
-                   struct drm_i915_gem_pwrite *args,
-                   struct drm_file *file_priv)
+i915_gem_gtt_pwrite_fast(struct drm_device *dev, struct drm_gem_object *obj,
+                        struct drm_i915_gem_pwrite *args,
+                        struct drm_file *file_priv)
 {
        struct drm_i915_gem_object *obj_priv = obj->driver_private;
        drm_i915_private_t *dev_priv = dev->dev_private;
@@ -273,7 +278,6 @@ i915_gem_gtt_pwrite(struct drm_device *dev, struct drm_gem_object *obj,
 
        obj_priv = obj->driver_private;
        offset = obj_priv->gtt_offset + args->offset;
-       obj_priv->dirty = 1;
 
        while (remain > 0) {
                /* Operation in this page
@@ -292,16 +296,11 @@ i915_gem_gtt_pwrite(struct drm_device *dev, struct drm_gem_object *obj,
                                       page_offset, user_data, page_length);
 
                /* If we get a fault while copying data, then (presumably) our
-                * source page isn't available. In this case, use the
-                * non-atomic function
+                * source page isn't available.  Return the error and we'll
+                * retry in the slow path.
                 */
-               if (ret) {
-                       ret = slow_user_write (dev_priv->mm.gtt_mapping,
-                                              page_base, page_offset,
-                                              user_data, page_length);
-                       if (ret)
-                               goto fail;
-               }
+               if (ret)
+                       goto fail;
 
                remain -= page_length;
                user_data += page_length;
@@ -315,6 +314,115 @@ fail:
        return ret;
 }
 
+/**
+ * This is the fallback GTT pwrite path, which uses get_user_pages to pin
+ * the memory and maps it using kmap_atomic for copying.
+ *
+ * This code resulted in x11perf -rgb10text consuming about 10% more CPU
+ * than using i915_gem_gtt_pwrite_fast on a G45 (32-bit).
+ */
+static int
+i915_gem_gtt_pwrite_slow(struct drm_device *dev, struct drm_gem_object *obj,
+                        struct drm_i915_gem_pwrite *args,
+                        struct drm_file *file_priv)
+{
+       struct drm_i915_gem_object *obj_priv = obj->driver_private;
+       drm_i915_private_t *dev_priv = dev->dev_private;
+       ssize_t remain;
+       loff_t gtt_page_base, offset;
+       loff_t first_data_page, last_data_page, num_pages;
+       loff_t pinned_pages, i;
+       struct page **user_pages;
+       struct mm_struct *mm = current->mm;
+       int gtt_page_offset, data_page_offset, data_page_index, 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, and all of the pwrite implementations
+        * 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 out_unpin_pages;
+       }
+
+       mutex_lock(&dev->struct_mutex);
+       ret = i915_gem_object_pin(obj, 0);
+       if (ret)
+               goto out_unlock;
+
+       ret = i915_gem_object_set_to_gtt_domain(obj, 1);
+       if (ret)
+               goto out_unpin_object;
+
+       obj_priv = obj->driver_private;
+       offset = obj_priv->gtt_offset + args->offset;
+
+       while (remain > 0) {
+               /* Operation in this page
+                *
+                * gtt_page_base = page offset within aperture
+                * gtt_page_offset = offset within page in aperture
+                * 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
+                */
+               gtt_page_base = offset & PAGE_MASK;
+               gtt_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 ((gtt_page_offset + page_length) > PAGE_SIZE)
+                       page_length = PAGE_SIZE - gtt_page_offset;
+               if ((data_page_offset + page_length) > PAGE_SIZE)
+                       page_length = PAGE_SIZE - data_page_offset;
+
+               ret = slow_kernel_write(dev_priv->mm.gtt_mapping,
+                                       gtt_page_base, gtt_page_offset,
+                                       user_pages[data_page_index],
+                                       data_page_offset,
+                                       page_length);
+
+               /* If we get a fault while copying data, then (presumably) our
+                * source page isn't available.  Return the error and we'll
+                * retry in the slow path.
+                */
+               if (ret)
+                       goto out_unpin_object;
+
+               remain -= page_length;
+               offset += page_length;
+               data_ptr += page_length;
+       }
+
+out_unpin_object:
+       i915_gem_object_unpin(obj);
+out_unlock:
+       mutex_unlock(&dev->struct_mutex);
+out_unpin_pages:
+       for (i = 0; i < pinned_pages; i++)
+               page_cache_release(user_pages[i]);
+       kfree(user_pages);
+
+       return ret;
+}
+
 static int
 i915_gem_shmem_pwrite(struct drm_device *dev, struct drm_gem_object *obj,
                      struct drm_i915_gem_pwrite *args,
@@ -388,9 +496,13 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
        if (obj_priv->phys_obj)
                ret = i915_gem_phys_pwrite(dev, obj, args, file_priv);
        else if (obj_priv->tiling_mode == I915_TILING_NONE &&
-                dev->gtt_total != 0)
-               ret = i915_gem_gtt_pwrite(dev, obj, args, file_priv);
-       else
+                dev->gtt_total != 0) {
+               ret = i915_gem_gtt_pwrite_fast(dev, obj, args, file_priv);
+               if (ret == -EFAULT) {
+                       ret = i915_gem_gtt_pwrite_slow(dev, obj, args,
+                                                      file_priv);
+               }
+       } else
                ret = i915_gem_shmem_pwrite(dev, obj, args, file_priv);
 
 #if WATCH_PWRITE