[PATCH 21/41] drm/i915: Implement pread without struct-mutex

[Chris Wilson <chris@chris-wilson.co.uk>]

We only need struct_mutex within pread for a brief window where we need
to serialise with rendering and control our cache domains. Elsewhere we
can rely on the backing storage being pinned, and forgive userspace any
races against us.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 365 +++++++++++++++++-----------------------
 1 file changed, 157 insertions(+), 208 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index bfa80302e2d5..ab119ea49634 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -63,13 +63,13 @@ static bool cpu_write_needs_clflush(struct drm_i915_gem_object *obj)
 }
 
 static int
-insert_mappable_node(struct drm_i915_private *i915,
+insert_mappable_node(struct i915_ggtt *ggtt,
                      struct drm_mm_node *node, u32 size)
 {
 	memset(node, 0, sizeof(*node));
-	return drm_mm_insert_node_in_range_generic(&i915->ggtt.base.mm, node,
-						   size, 0, 0, 0,
-						   i915->ggtt.mappable_end,
+	return drm_mm_insert_node_in_range_generic(&ggtt->base.mm, node,
+						   size, 0, -1,
+						   0, ggtt->mappable_end,
 						   DRM_MM_SEARCH_DEFAULT,
 						   DRM_MM_CREATE_DEFAULT);
 }
@@ -820,32 +820,6 @@ int i915_gem_obj_prepare_shmem_write(struct drm_i915_gem_object *obj,
 	return ret;
 }
 
-/* Per-page copy function for the shmem pread fastpath.
- * Flushes invalid cachelines before reading the target if
- * needs_clflush is set. */
-static int
-shmem_pread_fast(struct page *page, int shmem_page_offset, int page_length,
-		 char __user *user_data,
-		 bool page_do_bit17_swizzling, bool needs_clflush)
-{
-	char *vaddr;
-	int ret;
-
-	if (unlikely(page_do_bit17_swizzling))
-		return -EINVAL;
-
-	vaddr = kmap_atomic(page);
-	if (needs_clflush)
-		drm_clflush_virt_range(vaddr + shmem_page_offset,
-				       page_length);
-	ret = __copy_to_user_inatomic(user_data,
-				      vaddr + shmem_page_offset,
-				      page_length);
-	kunmap_atomic(vaddr);
-
-	return ret ? -EFAULT : 0;
-}
-
 static void
 shmem_clflush_swizzled_range(char *addr, unsigned long length,
 			     bool swizzled)
@@ -871,7 +845,7 @@ shmem_clflush_swizzled_range(char *addr, unsigned long length,
 /* Only difference to the fast-path function is that this can handle bit17
  * and uses non-atomic copy and kmap functions. */
 static int
-shmem_pread_slow(struct page *page, int shmem_page_offset, int page_length,
+shmem_pread_slow(struct page *page, int offset, int length,
 		 char __user *user_data,
 		 bool page_do_bit17_swizzling, bool needs_clflush)
 {
@@ -880,61 +854,130 @@ shmem_pread_slow(struct page *page, int shmem_page_offset, int page_length,
 
 	vaddr = kmap(page);
 	if (needs_clflush)
-		shmem_clflush_swizzled_range(vaddr + shmem_page_offset,
-					     page_length,
+		shmem_clflush_swizzled_range(vaddr + offset, length,
 					     page_do_bit17_swizzling);
 
 	if (page_do_bit17_swizzling)
-		ret = __copy_to_user_swizzled(user_data,
-					      vaddr, shmem_page_offset,
-					      page_length);
+		ret = __copy_to_user_swizzled(user_data, vaddr, offset, length);
 	else
-		ret = __copy_to_user(user_data,
-				     vaddr + shmem_page_offset,
-				     page_length);
+		ret = __copy_to_user(user_data, vaddr + offset, length);
 	kunmap(page);
 
 	return ret ? - EFAULT : 0;
 }
 
-static inline unsigned long
-slow_user_access(struct io_mapping *mapping,
-		 uint64_t page_base, int page_offset,
-		 char __user *user_data,
-		 unsigned long length, bool pwrite)
+static int
+shmem_pread(struct page *page, int offset, int length, char __user *user_data,
+	    bool page_do_bit17_swizzling, bool needs_clflush)
+{
+	int ret;
+
+	ret = -ENODEV;
+	if (!page_do_bit17_swizzling) {
+		char *vaddr = kmap_atomic(page);
+
+		if (needs_clflush)
+			drm_clflush_virt_range(vaddr + offset, length);
+		ret = __copy_to_user_inatomic(user_data, vaddr + offset, length);
+		kunmap_atomic(vaddr);
+	}
+	if (ret == 0)
+		return 0;
+
+	return shmem_pread_slow(page, offset, length, user_data,
+				page_do_bit17_swizzling, needs_clflush);
+}
+
+static int
+i915_gem_shmem_pread(struct drm_i915_gem_object *obj,
+		     struct drm_i915_gem_pread *args)
+{
+	char __user *user_data;
+	u64 remain;
+	unsigned int obj_do_bit17_swizzling;
+	unsigned int needs_clflush;
+	unsigned int idx, offset;
+	int ret;
+
+	obj_do_bit17_swizzling = 0;
+	if (i915_gem_object_needs_bit17_swizzle(obj))
+		obj_do_bit17_swizzling = BIT(17);
+
+	ret = mutex_lock_interruptible(&obj->base.dev->struct_mutex);
+	if (ret)
+		return ret;
+
+	ret = i915_gem_obj_prepare_shmem_read(obj, &needs_clflush);
+	mutex_unlock(&obj->base.dev->struct_mutex);
+	if (ret)
+		return ret;
+
+	remain = args->size;
+	user_data = u64_to_user_ptr(args->data_ptr);
+	offset = offset_in_page(args->offset);
+	for (idx = args->offset >> PAGE_SHIFT; remain; idx++) {
+		struct page *page = i915_gem_object_get_page(obj, idx);
+		int length;
+
+		length = remain;
+		if (offset + length > PAGE_SIZE)
+			length = PAGE_SIZE - offset;
+
+		ret = shmem_pread(page, offset, length, user_data,
+				  page_to_phys(page) & obj_do_bit17_swizzling,
+				  needs_clflush);
+		if (ret)
+			break;
+
+		remain -= length;
+		user_data += length;
+		offset = 0;
+	}
+
+	i915_gem_obj_finish_shmem_access(obj);
+	return ret;
+}
+
+static inline bool
+gtt_user_read(struct io_mapping *mapping,
+	      loff_t base, int offset,
+	      char __user *user_data, int length)
 {
-	void __iomem *ioaddr;
 	void *vaddr;
-	uint64_t unwritten;
+	unsigned long unwritten;
 
-	ioaddr = io_mapping_map_wc(mapping, page_base, PAGE_SIZE);
 	/* We can use the cpu mem copy function because this is X86. */
-	vaddr = (void __force *)ioaddr + page_offset;
-	if (pwrite)
-		unwritten = __copy_from_user(vaddr, user_data, length);
-	else
-		unwritten = __copy_to_user(user_data, vaddr, length);
-
-	io_mapping_unmap(ioaddr);
+	vaddr =(void __force *)io_mapping_map_atomic_wc(mapping, base);
+	unwritten = __copy_to_user_inatomic(user_data, vaddr + offset, length);
+	io_mapping_unmap_atomic(vaddr);
+	if (unwritten) {
+		vaddr = (void __force *)
+			io_mapping_map_wc(mapping, base, PAGE_SIZE);
+		unwritten = copy_to_user(user_data, vaddr + offset, length);
+		io_mapping_unmap(vaddr);
+	}
 	return unwritten;
 }
 
 static int
-i915_gem_gtt_pread(struct drm_device *dev,
-		   struct drm_i915_gem_object *obj, uint64_t size,
-		   uint64_t data_offset, uint64_t data_ptr)
+i915_gem_gtt_pread(struct drm_i915_gem_object *obj,
+		   const struct drm_i915_gem_pread *args)
 {
-	struct drm_i915_private *dev_priv = to_i915(dev);
-	struct i915_ggtt *ggtt = &dev_priv->ggtt;
-	struct i915_vma *vma;
+	struct drm_i915_private *i915 = to_i915(obj->base.dev);
+	struct i915_ggtt *ggtt = &i915->ggtt;
 	struct drm_mm_node node;
-	char __user *user_data;
-	uint64_t remain;
-	uint64_t offset;
+	struct i915_vma *vma;
+	void __user *user_data;
+	u64 remain, offset;
 	int ret;
 
-	intel_runtime_pm_get(to_i915(dev));
-	vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0, PIN_MAPPABLE);
+	ret = mutex_lock_interruptible(&i915->drm.struct_mutex);
+	if (ret)
+		return ret;
+
+	intel_runtime_pm_get(i915);
+	vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0,
+				       PIN_MAPPABLE | PIN_NONBLOCK);
 	if (!IS_ERR(vma)) {
 		node.start = i915_ggtt_offset(vma);
 		node.allocated = false;
@@ -945,33 +988,21 @@ i915_gem_gtt_pread(struct drm_device *dev,
 		}
 	}
 	if (IS_ERR(vma)) {
-		ret = insert_mappable_node(dev_priv, &node, PAGE_SIZE);
+		ret = insert_mappable_node(ggtt, &node, PAGE_SIZE);
 		if (ret)
-			goto out;
-
-		ret = i915_gem_object_pin_pages(obj);
-		if (ret) {
-			remove_mappable_node(&node);
-			goto out;
-		}
+			goto out_unlock;
+		GEM_BUG_ON(!node.allocated);
 	}
 
 	ret = i915_gem_object_set_to_gtt_domain(obj, false);
 	if (ret)
 		goto out_unpin;
 
-	user_data = u64_to_user_ptr(data_ptr);
-	remain = size;
-	offset = data_offset;
+	mutex_unlock(&i915->drm.struct_mutex);
 
-	mutex_unlock(&dev->struct_mutex);
-	if (likely(!i915.prefault_disable)) {
-		ret = fault_in_pages_writeable(user_data, remain);
-		if (ret) {
-			mutex_lock(&dev->struct_mutex);
-			goto out_unpin;
-		}
-	}
+	user_data = u64_to_user_ptr(args->data_ptr);
+	remain = args->size;
+	offset = args->offset;
 
 	while (remain > 0) {
 		/* Operation in this page
@@ -988,19 +1019,14 @@ i915_gem_gtt_pread(struct drm_device *dev,
 			wmb();
 			ggtt->base.insert_page(&ggtt->base,
 					       i915_gem_object_get_dma_address(obj, offset >> PAGE_SHIFT),
-					       node.start,
-					       I915_CACHE_NONE, 0);
+					       node.start, I915_CACHE_NONE, 0);
 			wmb();
 		} else {
 			page_base += offset & PAGE_MASK;
 		}
-		/* This is a slow read/write as it tries to read from
-		 * and write to user memory which may result into page
-		 * faults, and so we cannot perform this under struct_mutex.
-		 */
-		if (slow_user_access(&ggtt->mappable, page_base,
-				     page_offset, user_data,
-				     page_length, false)) {
+
+		if (gtt_user_read(&ggtt->mappable, page_base, page_offset,
+				  user_data, page_length)) {
 			ret = -EFAULT;
 			break;
 		}
@@ -1010,111 +1036,19 @@ i915_gem_gtt_pread(struct drm_device *dev,
 		offset += page_length;
 	}
 
-	mutex_lock(&dev->struct_mutex);
-	if (ret == 0 && (obj->base.read_domains & I915_GEM_DOMAIN_GTT) == 0) {
-		/* The user has modified the object whilst we tried
-		 * reading from it, and we now have no idea what domain
-		 * the pages should be in. As we have just been touching
-		 * them directly, flush everything back to the GTT
-		 * domain.
-		 */
-		ret = i915_gem_object_set_to_gtt_domain(obj, false);
-	}
-
+	mutex_lock(&i915->drm.struct_mutex);
 out_unpin:
 	if (node.allocated) {
 		wmb();
 		ggtt->base.clear_range(&ggtt->base,
 				       node.start, node.size);
-		i915_gem_object_unpin_pages(obj);
 		remove_mappable_node(&node);
 	} else {
 		i915_vma_unpin(vma);
 	}
-out:
-	intel_runtime_pm_put(to_i915(dev));
-	return ret;
-}
-
-static int
-i915_gem_shmem_pread(struct drm_device *dev,
-		     struct drm_i915_gem_object *obj,
-		     struct drm_i915_gem_pread *args,
-		     struct drm_file *file)
-{
-	char __user *user_data;
-	ssize_t remain;
-	loff_t offset;
-	int shmem_page_offset, page_length, ret = 0;
-	int obj_do_bit17_swizzling, page_do_bit17_swizzling;
-	int prefaulted = 0;
-	int needs_clflush = 0;
-	struct sg_page_iter sg_iter;
-
-	ret = i915_gem_obj_prepare_shmem_read(obj, &needs_clflush);
-	if (ret)
-		return ret;
-
-	obj_do_bit17_swizzling = i915_gem_object_needs_bit17_swizzle(obj);
-	user_data = u64_to_user_ptr(args->data_ptr);
-	offset = args->offset;
-	remain = args->size;
-
-	for_each_sg_page(obj->mm.pages->sgl, &sg_iter, obj->mm.pages->nents,
-			 offset >> PAGE_SHIFT) {
-		struct page *page = sg_page_iter_page(&sg_iter);
-
-		if (remain <= 0)
-			break;
-
-		/* Operation in this page
-		 *
-		 * shmem_page_offset = offset within page in shmem file
-		 * page_length = bytes to copy for this page
-		 */
-		shmem_page_offset = offset_in_page(offset);
-		page_length = remain;
-		if ((shmem_page_offset + page_length) > PAGE_SIZE)
-			page_length = PAGE_SIZE - shmem_page_offset;
-
-		page_do_bit17_swizzling = obj_do_bit17_swizzling &&
-			(page_to_phys(page) & (1 << 17)) != 0;
-
-		ret = shmem_pread_fast(page, shmem_page_offset, page_length,
-				       user_data, page_do_bit17_swizzling,
-				       needs_clflush);
-		if (ret == 0)
-			goto next_page;
-
-		mutex_unlock(&dev->struct_mutex);
-
-		if (likely(!i915.prefault_disable) && !prefaulted) {
-			ret = fault_in_pages_writeable(user_data, remain);
-			/* Userspace is tricking us, but we've already clobbered
-			 * its pages with the prefault and promised to write the
-			 * data up to the first fault. Hence ignore any errors
-			 * and just continue. */
-			(void)ret;
-			prefaulted = 1;
-		}
-
-		ret = shmem_pread_slow(page, shmem_page_offset, page_length,
-				       user_data, page_do_bit17_swizzling,
-				       needs_clflush);
-
-		mutex_lock(&dev->struct_mutex);
-
-		if (ret)
-			goto out;
-
-next_page:
-		remain -= page_length;
-		user_data += page_length;
-		offset += page_length;
-	}
-
-out:
-	i915_gem_obj_finish_shmem_access(obj);
+out_unlock:
+	intel_runtime_pm_put(i915);
+	mutex_unlock(&i915->drm.struct_mutex);
 
 	return ret;
 }
@@ -1133,7 +1067,7 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
 {
 	struct drm_i915_gem_pread *args = data;
 	struct drm_i915_gem_object *obj;
-	int ret = 0;
+	int ret;
 
 	if (args->size == 0)
 		return 0;
@@ -1151,7 +1085,7 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
 	if (args->offset > obj->base.size ||
 	    args->size > obj->base.size - args->offset) {
 		ret = -EINVAL;
-		goto err;
+		goto out;
 	}
 
 	trace_i915_gem_object_pread(obj, args->offset, args->size);
@@ -1161,25 +1095,18 @@ i915_gem_pread_ioctl(struct drm_device *dev, void *data,
 				   MAX_SCHEDULE_TIMEOUT,
 				   to_rps_client(file));
 	if (ret)
-		goto err;
+		goto out;
 
-	ret = i915_mutex_lock_interruptible(dev);
+	ret = i915_gem_object_pin_pages(obj);
 	if (ret)
-		goto err;
-
-	ret = i915_gem_shmem_pread(dev, obj, args, file);
+		goto out;
 
-	/* pread for non shmem backed objects */
+	ret = i915_gem_shmem_pread(obj, args);
 	if (ret == -EFAULT || ret == -ENODEV)
-		ret = i915_gem_gtt_pread(dev, obj, args->size,
-					args->offset, args->data_ptr);
-
-	i915_gem_object_put(obj);
-	mutex_unlock(&dev->struct_mutex);
-
-	return ret;
+		ret = i915_gem_gtt_pread(obj, args);
 
-err:
+	i915_gem_object_unpin_pages(obj);
+out:
 	i915_gem_object_put_unlocked(obj);
 	return ret;
 }
@@ -1207,6 +1134,28 @@ fast_user_write(struct io_mapping *mapping,
 	return unwritten;
 }
 
+static inline unsigned long
+slow_user_access(struct io_mapping *mapping,
+		 unsigned long page_base, int page_offset,
+		 char __user *user_data,
+		 unsigned long length, bool pwrite)
+{
+	void __iomem *ioaddr;
+	void *vaddr;
+	unsigned long unwritten;
+
+	ioaddr = io_mapping_map_wc(mapping, page_base, PAGE_SIZE);
+	/* We can use the cpu mem copy function because this is X86. */
+	vaddr = (void __force *)ioaddr + page_offset;
+	if (pwrite)
+		unwritten = __copy_from_user(vaddr, user_data, length);
+	else
+		unwritten = __copy_to_user(user_data, vaddr, length);
+
+	io_mapping_unmap(ioaddr);
+	return unwritten;
+}
+
 /**
  * This is the fast pwrite path, where we copy the data directly from the
  * user into the GTT, uncached.
@@ -1246,7 +1195,7 @@ i915_gem_gtt_pwrite_fast(struct drm_i915_private *i915,
 		}
 	}
 	if (IS_ERR(vma)) {
-		ret = insert_mappable_node(i915, &node, PAGE_SIZE);
+		ret = insert_mappable_node(ggtt, &node, PAGE_SIZE);
 		if (ret)
 			goto out;
 
@@ -1275,8 +1224,8 @@ i915_gem_gtt_pwrite_fast(struct drm_i915_private *i915,
 		 * page_length = bytes to copy for this page
 		 */
 		u32 page_base = node.start;
-		unsigned page_offset = offset_in_page(offset);
-		unsigned page_length = PAGE_SIZE - page_offset;
+		unsigned int page_offset = offset_in_page(offset);
+		unsigned int page_length = PAGE_SIZE - page_offset;
 		page_length = remain < page_length ? remain : page_length;
 		if (node.allocated) {
 			wmb(); /* flush the write before we modify the GGTT */
-- 
2.9.3

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