drm/i915: Rework struct phys attachment handling

Instead of creating a separate object type, we make changes to
the shmem type, to clear struct page backing. This will allow us to
ensure we never run into a race when we exchange obj->ops with other
function pointers.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-9-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -37,7 +37,15 @@ void __i915_gem_object_release_shmem(struct drm_i915_gem_object *obj,
 				     struct sg_table *pages,
 				     bool needs_clflush);
 
+int i915_gem_object_pwrite_phys(struct drm_i915_gem_object *obj,
+				const struct drm_i915_gem_pwrite *args);
+int i915_gem_object_pread_phys(struct drm_i915_gem_object *obj,
+			       const struct drm_i915_gem_pread *args);
+
 int i915_gem_object_attach_phys(struct drm_i915_gem_object *obj, int align);
+void i915_gem_object_put_pages_phys(struct drm_i915_gem_object *obj,
+				    struct sg_table *pages);
+
 
 void i915_gem_flush_free_objects(struct drm_i915_private *i915);
 

drivers/gpu/drm/i915/gem/i915_gem_phys.c

@@ -76,6 +76,8 @@ static int i915_gem_object_get_pages_phys(struct drm_i915_gem_object *obj)
 
 	intel_gt_chipset_flush(&to_i915(obj->base.dev)->gt);
 
+	/* We're no longer struct page backed */
+	obj->flags &= ~I915_BO_ALLOC_STRUCT_PAGE;
 	__i915_gem_object_set_pages(obj, st, sg->length);
 
 	return 0;
@@ -89,7 +91,7 @@ static int i915_gem_object_get_pages_phys(struct drm_i915_gem_object *obj)
 	return -ENOMEM;
 }
 
-static void
+void
 i915_gem_object_put_pages_phys(struct drm_i915_gem_object *obj,
 			       struct sg_table *pages)
 {
@@ -134,8 +136,7 @@ i915_gem_object_put_pages_phys(struct drm_i915_gem_object *obj,
 			  vaddr, dma);
 }
 
-static int
-phys_pwrite(struct drm_i915_gem_object *obj,
+int i915_gem_object_pwrite_phys(struct drm_i915_gem_object *obj,
 				const struct drm_i915_gem_pwrite *args)
 {
 	void *vaddr = sg_page(obj->mm.pages->sgl) + args->offset;
@@ -165,8 +166,7 @@ phys_pwrite(struct drm_i915_gem_object *obj,
 	return 0;
 }
 
-static int
-phys_pread(struct drm_i915_gem_object *obj,
+int i915_gem_object_pread_phys(struct drm_i915_gem_object *obj,
 			       const struct drm_i915_gem_pread *args)
 {
 	void *vaddr = sg_page(obj->mm.pages->sgl) + args->offset;
@@ -186,86 +186,82 @@ phys_pread(struct drm_i915_gem_object *obj,
 	return 0;
 }
 
-static void phys_release(struct drm_i915_gem_object *obj)
+static int i915_gem_object_shmem_to_phys(struct drm_i915_gem_object *obj)
 {
-	fput(obj->base.filp);
-}
+	struct sg_table *pages;
+	int err;
 
-static const struct drm_i915_gem_object_ops i915_gem_phys_ops = {
-	.name = "i915_gem_object_phys",
-	.get_pages = i915_gem_object_get_pages_phys,
-	.put_pages = i915_gem_object_put_pages_phys,
+	pages = __i915_gem_object_unset_pages(obj);
+
+	err = i915_gem_object_get_pages_phys(obj);
+	if (err)
+		goto err_xfer;
 
-	.pread  = phys_pread,
-	.pwrite = phys_pwrite,
+	/* Perma-pin (until release) the physical set of pages */
+	__i915_gem_object_pin_pages(obj);
 
-	.release = phys_release,
-};
+	if (!IS_ERR_OR_NULL(pages))
+		i915_gem_shmem_ops.put_pages(obj, pages);
+
+	i915_gem_object_release_memory_region(obj);
+	return 0;
+
+err_xfer:
+	if (!IS_ERR_OR_NULL(pages)) {
+		unsigned int sg_page_sizes = i915_sg_page_sizes(pages->sgl);
+
+		__i915_gem_object_set_pages(obj, pages, sg_page_sizes);
+	}
+	return err;
+}
 
 int i915_gem_object_attach_phys(struct drm_i915_gem_object *obj, int align)
 {
-	struct sg_table *pages;
 	int err;
 
 	if (align > obj->base.size)
 		return -EINVAL;
 
-	if (obj->ops == &i915_gem_phys_ops)
-		return 0;
-
 	if (!i915_gem_object_is_shmem(obj))
 		return -EINVAL;
 
+	if (!i915_gem_object_has_struct_page(obj))
+		return 0;
+
 	err = i915_gem_object_unbind(obj, I915_GEM_OBJECT_UNBIND_ACTIVE);
 	if (err)
 		return err;
 
 	mutex_lock_nested(&obj->mm.lock, I915_MM_GET_PAGES);
 
+	if (unlikely(!i915_gem_object_has_struct_page(obj)))
+		goto out;
+
 	if (obj->mm.madv != I915_MADV_WILLNEED) {
 		err = -EFAULT;
-		goto err_unlock;
+		goto out;
 	}
 
 	if (i915_gem_object_has_tiling_quirk(obj)) {
 		err = -EFAULT;
-		goto err_unlock;
+		goto out;
 	}
 
-	if (obj->mm.mapping) {
+	if (obj->mm.mapping || i915_gem_object_has_pinned_pages(obj)) {
 		err = -EBUSY;
-		goto err_unlock;
+		goto out;
 	}
 
-	pages = __i915_gem_object_unset_pages(obj);
-
-	obj->ops = &i915_gem_phys_ops;
-	obj->flags &= ~I915_BO_ALLOC_STRUCT_PAGE;
-
-	err = ____i915_gem_object_get_pages(obj);
-	if (err)
-		goto err_xfer;
-
-	/* Perma-pin (until release) the physical set of pages */
-	__i915_gem_object_pin_pages(obj);
-
-	if (!IS_ERR_OR_NULL(pages))
-		i915_gem_shmem_ops.put_pages(obj, pages);
-
-	i915_gem_object_release_memory_region(obj);
-
-	mutex_unlock(&obj->mm.lock);
-	return 0;
+	if (unlikely(obj->mm.madv != I915_MADV_WILLNEED)) {
+		drm_dbg(obj->base.dev,
+			"Attempting to obtain a purgeable object\n");
+		err = -EFAULT;
+		goto out;
+	}
 
-err_xfer:
-	obj->ops = &i915_gem_shmem_ops;
-	obj->flags |= I915_BO_ALLOC_STRUCT_PAGE;
-	if (!IS_ERR_OR_NULL(pages)) {
-		unsigned int sg_page_sizes = i915_sg_page_sizes(pages->sgl);
+	err = i915_gem_object_shmem_to_phys(obj);
 
-		__i915_gem_object_set_pages(obj, pages, sg_page_sizes);
-	}
-err_unlock:
+out:
 	mutex_unlock(&obj->mm.lock);
 	return err;
 }

drivers/gpu/drm/i915/gem/i915_gem_shmem.c

@@ -303,6 +303,11 @@ shmem_put_pages(struct drm_i915_gem_object *obj, struct sg_table *pages)
 	struct pagevec pvec;
 	struct page *page;
 
+	if (unlikely(!i915_gem_object_has_struct_page(obj))) {
+		i915_gem_object_put_pages_phys(obj, pages);
+		return;
+	}
+
 	__i915_gem_object_release_shmem(obj, pages, true);
 
 	i915_gem_gtt_finish_pages(obj, pages);
@@ -343,6 +348,9 @@ shmem_pwrite(struct drm_i915_gem_object *obj,
 	/* Caller already validated user args */
 	GEM_BUG_ON(!access_ok(user_data, arg->size));
 
+	if (!i915_gem_object_has_struct_page(obj))
+		return i915_gem_object_pwrite_phys(obj, arg);
+
 	/*
 	 * Before we instantiate/pin the backing store for our use, we
 	 * can prepopulate the shmemfs filp efficiently using a write into
@@ -421,8 +429,19 @@ shmem_pwrite(struct drm_i915_gem_object *obj,
 	return 0;
 }
 
+static int
+shmem_pread(struct drm_i915_gem_object *obj,
+	    const struct drm_i915_gem_pread *arg)
+{
+	if (!i915_gem_object_has_struct_page(obj))
+		return i915_gem_object_pread_phys(obj, arg);
+
+	return -ENODEV;
+}
+
 static void shmem_release(struct drm_i915_gem_object *obj)
 {
+	if (obj->flags & I915_BO_ALLOC_STRUCT_PAGE)
 		i915_gem_object_release_memory_region(obj);
 
 	fput(obj->base.filp);
@@ -438,6 +457,7 @@ const struct drm_i915_gem_object_ops i915_gem_shmem_ops = {
 	.writeback = shmem_writeback,
 
 	.pwrite = shmem_pwrite,
+	.pread = shmem_pread,
 
 	.release = shmem_release,
 };

drivers/gpu/drm/i915/gem/selftests/i915_gem_phys.c

@@ -38,12 +38,6 @@ static int mock_phys_object(void *arg)
 	}
 
 	if (i915_gem_object_has_struct_page(obj)) {
-		err = -EINVAL;
-		pr_err("shmem has a struct page\n");
-		goto out_obj;
-	}
-
-	if (obj->ops != &i915_gem_phys_ops) {
 		pr_err("i915_gem_object_attach_phys did not create a phys object\n");
 		err = -EINVAL;
 		goto out_obj;