drm: Add library for shmem backed GEM objects

This adds a library for shmem backed GEM objects.

v8:
- export drm_gem_shmem_create_with_handle
- call mapping_set_gfp_mask to set default zone to GFP_HIGHUSER
- Add helper drm_gem_shmem_get_pages_sgt()

v7:
- Use write-combine for mmap instead. This is the more common
  case. (robher)

v6:
- Fix uninitialized variable issue in an error path (anholt).
- Add a drm_gem_shmem_vm_open() to the fops to get proper refcounting
  of the pages (anholt).

v5:
- Drop drm_gem_shmem_prime_mmap() (Daniel Vetter)
- drm_gem_shmem_mmap(): Subtract drm_vma_node_start() to get the real
  vma->vm_pgoff
- drm_gem_shmem_fault(): Use vmf->pgoff now that vma->vm_pgoff is correct

v4:
- Drop cache modes (Thomas Hellstrom)
- Add a GEM attached vtable

v3:
- Grammar (Sam Ravnborg)
- s/drm_gem_shmem_put_pages_unlocked/drm_gem_shmem_put_pages_locked/
  (Sam Ravnborg)
- Add debug output in error path (Sam Ravnborg)
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190313004344.24169-1-robh@kernel.org

Documentation/gpu/drm-kms-helpers.rst

@@ -369,3 +369,15 @@ Legacy CRTC/Modeset Helper Functions Reference
 
 .. kernel-doc:: drivers/gpu/drm/drm_crtc_helper.c
    :export:
+
+SHMEM GEM Helper Reference
+==========================
+
+.. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_helper.c
+   :doc: overview
+
+.. kernel-doc:: include/drm/drm_gem_shmem_helper.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_gem_shmem_helper.c
+   :export:

drivers/gpu/drm/Kconfig

@@ -173,6 +173,12 @@ config DRM_KMS_CMA_HELPER
 	help
 	  Choose this if you need the KMS CMA helper functions
 
+config DRM_GEM_SHMEM_HELPER
+	bool
+	depends on DRM
+	help
+	  Choose this if you need the GEM shmem helper functions
+
 config DRM_VM
 	bool
 	depends on DRM && MMU

drivers/gpu/drm/Makefile

@@ -25,6 +25,7 @@ drm-$(CONFIG_DRM_LIB_RANDOM) += lib/drm_random.o
 drm-$(CONFIG_DRM_VM) += drm_vm.o
 drm-$(CONFIG_COMPAT) += drm_ioc32.o
 drm-$(CONFIG_DRM_GEM_CMA_HELPER) += drm_gem_cma_helper.o
+drm-$(CONFIG_DRM_GEM_SHMEM_HELPER) += drm_gem_shmem_helper.o
 drm-$(CONFIG_PCI) += ati_pcigart.o
 drm-$(CONFIG_DRM_PANEL) += drm_panel.o
 drm-$(CONFIG_OF) += drm_of.o

drivers/gpu/drm/drm_gem_shmem_helper.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2018 Noralf Trønnes
+ */
+
+#include <linux/dma-buf.h>
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/shmem_fs.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+#include <drm/drm_device.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_gem_shmem_helper.h>
+#include <drm/drm_prime.h>
+#include <drm/drm_print.h>
+
+/**
+ * DOC: overview
+ *
+ * This library provides helpers for GEM objects backed by shmem buffers
+ * allocated using anonymous pageable memory.
+ */
+
+static const struct drm_gem_object_funcs drm_gem_shmem_funcs = {
+	.free = drm_gem_shmem_free_object,
+	.print_info = drm_gem_shmem_print_info,
+	.pin = drm_gem_shmem_pin,
+	.unpin = drm_gem_shmem_unpin,
+	.get_sg_table = drm_gem_shmem_get_sg_table,
+	.vmap = drm_gem_shmem_vmap,
+	.vunmap = drm_gem_shmem_vunmap,
+	.vm_ops = &drm_gem_shmem_vm_ops,
+};
+
+/**
+ * drm_gem_shmem_create - Allocate an object with the given size
+ * @dev: DRM device
+ * @size: Size of the object to allocate
+ *
+ * This function creates a shmem GEM object.
+ *
+ * Returns:
+ * A struct drm_gem_shmem_object * on success or an ERR_PTR()-encoded negative
+ * error code on failure.
+ */
+struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size)
+{
+	struct drm_gem_shmem_object *shmem;
+	struct drm_gem_object *obj;
+	int ret;
+
+	size = PAGE_ALIGN(size);
+
+	if (dev->driver->gem_create_object)
+		obj = dev->driver->gem_create_object(dev, size);
+	else
+		obj = kzalloc(sizeof(*shmem), GFP_KERNEL);
+	if (!obj)
+		return ERR_PTR(-ENOMEM);
+
+	if (!obj->funcs)
+		obj->funcs = &drm_gem_shmem_funcs;
+
+	ret = drm_gem_object_init(dev, obj, size);
+	if (ret)
+		goto err_free;
+
+	ret = drm_gem_create_mmap_offset(obj);
+	if (ret)
+		goto err_release;
+
+	shmem = to_drm_gem_shmem_obj(obj);
+	mutex_init(&shmem->pages_lock);
+	mutex_init(&shmem->vmap_lock);
+
+	/*
+	 * Our buffers are kept pinned, so allocating them
+	 * from the MOVABLE zone is a really bad idea, and
+	 * conflicts with CMA. See comments above new_inode()
+	 * why this is required _and_ expected if you're
+	 * going to pin these pages.
+	 */
+	mapping_set_gfp_mask(obj->filp->f_mapping, GFP_HIGHUSER |
+			     __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
+
+	return shmem;
+
+err_release:
+	drm_gem_object_release(obj);
+err_free:
+	kfree(obj);
+
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_create);
+
+/**
+ * drm_gem_shmem_free_object - Free resources associated with a shmem GEM object
+ * @obj: GEM object to free
+ *
+ * This function cleans up the GEM object state and frees the memory used to
+ * store the object itself.
+ */
+void drm_gem_shmem_free_object(struct drm_gem_object *obj)
+{
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	WARN_ON(shmem->vmap_use_count);
+
+	if (obj->import_attach) {
+		shmem->pages_use_count--;
+		drm_prime_gem_destroy(obj, shmem->sgt);
+		kvfree(shmem->pages);
+	} else {
+		if (shmem->sgt) {
+			dma_unmap_sg(obj->dev->dev, shmem->sgt->sgl,
+				     shmem->sgt->nents, DMA_BIDIRECTIONAL);
+
+			drm_gem_shmem_put_pages(shmem);
+			sg_free_table(shmem->sgt);
+			kfree(shmem->sgt);
+		}
+	}
+
+	WARN_ON(shmem->pages_use_count);
+
+	drm_gem_object_release(obj);
+	mutex_destroy(&shmem->pages_lock);
+	mutex_destroy(&shmem->vmap_lock);
+	kfree(shmem);
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_free_object);
+
+static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
+{
+	struct drm_gem_object *obj = &shmem->base;
+	struct page **pages;
+
+	if (shmem->pages_use_count++ > 0)
+		return 0;
+
+	pages = drm_gem_get_pages(obj);
+	if (IS_ERR(pages)) {
+		DRM_DEBUG_KMS("Failed to get pages (%ld)\n", PTR_ERR(pages));
+		shmem->pages_use_count = 0;
+		return PTR_ERR(pages);
+	}
+
+	shmem->pages = pages;
+
+	return 0;
+}
+
+/*
+ * drm_gem_shmem_get_pages - Allocate backing pages for a shmem GEM object
+ * @shmem: shmem GEM object
+ *
+ * This function makes sure that backing pages exists for the shmem GEM object
+ * and increases the use count.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
+ */
+int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
+{
+	int ret;
+
+	ret = mutex_lock_interruptible(&shmem->pages_lock);
+	if (ret)
+		return ret;
+	ret = drm_gem_shmem_get_pages_locked(shmem);
+	mutex_unlock(&shmem->pages_lock);
+
+	return ret;
+}
+EXPORT_SYMBOL(drm_gem_shmem_get_pages);
+
+static void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
+{
+	struct drm_gem_object *obj = &shmem->base;
+
+	if (WARN_ON_ONCE(!shmem->pages_use_count))
+		return;
+
+	if (--shmem->pages_use_count > 0)
+		return;
+
+	drm_gem_put_pages(obj, shmem->pages,
+			  shmem->pages_mark_dirty_on_put,
+			  shmem->pages_mark_accessed_on_put);
+	shmem->pages = NULL;
+}
+
+/*
+ * drm_gem_shmem_put_pages - Decrease use count on the backing pages for a shmem GEM object
+ * @shmem: shmem GEM object
+ *
+ * This function decreases the use count and puts the backing pages when use drops to zero.
+ */
+void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
+{
+	mutex_lock(&shmem->pages_lock);
+	drm_gem_shmem_put_pages_locked(shmem);
+	mutex_unlock(&shmem->pages_lock);
+}
+EXPORT_SYMBOL(drm_gem_shmem_put_pages);
+
+/**
+ * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object
+ * @obj: GEM object
+ *
+ * This function makes sure the backing pages are pinned in memory while the
+ * buffer is exported.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
+ */
+int drm_gem_shmem_pin(struct drm_gem_object *obj)
+{
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	return drm_gem_shmem_get_pages(shmem);
+}
+EXPORT_SYMBOL(drm_gem_shmem_pin);
+
+/**
+ * drm_gem_shmem_unpin - Unpin backing pages for a shmem GEM object
+ * @obj: GEM object
+ *
+ * This function removes the requirement that the backing pages are pinned in
+ * memory.
+ */
+void drm_gem_shmem_unpin(struct drm_gem_object *obj)
+{
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	drm_gem_shmem_put_pages(shmem);
+}
+EXPORT_SYMBOL(drm_gem_shmem_unpin);
+
+static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
+{
+	struct drm_gem_object *obj = &shmem->base;
+	int ret;
+
+	if (shmem->vmap_use_count++ > 0)
+		return shmem->vaddr;
+
+	ret = drm_gem_shmem_get_pages(shmem);
+	if (ret)
+		goto err_zero_use;
+
+	if (obj->import_attach)
+		shmem->vaddr = dma_buf_vmap(obj->import_attach->dmabuf);
+	else
+		shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT, VM_MAP, PAGE_KERNEL);
+
+	if (!shmem->vaddr) {
+		DRM_DEBUG_KMS("Failed to vmap pages\n");
+		ret = -ENOMEM;
+		goto err_put_pages;
+	}
+
+	return shmem->vaddr;
+
+err_put_pages:
+	drm_gem_shmem_put_pages(shmem);
+err_zero_use:
+	shmem->vmap_use_count = 0;
+
+	return ERR_PTR(ret);
+}
+
+/*
+ * drm_gem_shmem_vmap - Create a virtual mapping for a shmem GEM object
+ * @shmem: shmem GEM object
+ *
+ * This function makes sure that a virtual address exists for the buffer backing
+ * the shmem GEM object.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
+ */
+void *drm_gem_shmem_vmap(struct drm_gem_object *obj)
+{
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+	void *vaddr;
+	int ret;
+
+	ret = mutex_lock_interruptible(&shmem->vmap_lock);
+	if (ret)
+		return ERR_PTR(ret);
+	vaddr = drm_gem_shmem_vmap_locked(shmem);
+	mutex_unlock(&shmem->vmap_lock);
+
+	return vaddr;
+}
+EXPORT_SYMBOL(drm_gem_shmem_vmap);
+
+static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem)
+{
+	struct drm_gem_object *obj = &shmem->base;
+
+	if (WARN_ON_ONCE(!shmem->vmap_use_count))
+		return;
+
+	if (--shmem->vmap_use_count > 0)
+		return;
+
+	if (obj->import_attach)
+		dma_buf_vunmap(obj->import_attach->dmabuf, shmem->vaddr);
+	else
+		vunmap(shmem->vaddr);
+
+	shmem->vaddr = NULL;
+	drm_gem_shmem_put_pages(shmem);
+}
+
+/*
+ * drm_gem_shmem_vunmap - Unmap a virtual mapping fo a shmem GEM object
+ * @shmem: shmem GEM object
+ *
+ * This function removes the virtual address when use count drops to zero.
+ */
+void drm_gem_shmem_vunmap(struct drm_gem_object *obj, void *vaddr)
+{
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	mutex_lock(&shmem->vmap_lock);
+	drm_gem_shmem_vunmap_locked(shmem);
+	mutex_unlock(&shmem->vmap_lock);
+}
+EXPORT_SYMBOL(drm_gem_shmem_vunmap);
+
+struct drm_gem_shmem_object *
+drm_gem_shmem_create_with_handle(struct drm_file *file_priv,
+				 struct drm_device *dev, size_t size,
+				 uint32_t *handle)
+{
+	struct drm_gem_shmem_object *shmem;
+	int ret;
+
+	shmem = drm_gem_shmem_create(dev, size);
+	if (IS_ERR(shmem))
+		return shmem;
+
+	/*
+	 * Allocate an id of idr table where the obj is registered
+	 * and handle has the id what user can see.
+	 */
+	ret = drm_gem_handle_create(file_priv, &shmem->base, handle);
+	/* drop reference from allocate - handle holds it now. */
+	drm_gem_object_put_unlocked(&shmem->base);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return shmem;
+}
+EXPORT_SYMBOL(drm_gem_shmem_create_with_handle);
+
+/**
+ * drm_gem_shmem_dumb_create - Create a dumb shmem buffer object
+ * @file: DRM file structure to create the dumb buffer for
+ * @dev: DRM device
+ * @args: IOCTL data
+ *
+ * This function computes the pitch of the dumb buffer and rounds it up to an
+ * integer number of bytes per pixel. Drivers for hardware that doesn't have
+ * any additional restrictions on the pitch can directly use this function as
+ * their &drm_driver.dumb_create callback.
+ *
+ * For hardware with additional restrictions, drivers can adjust the fields
+ * set up by userspace before calling into this function.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
+ */
+int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
+			      struct drm_mode_create_dumb *args)
+{
+	u32 min_pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
+	struct drm_gem_shmem_object *shmem;
+
+	if (!args->pitch || !args->size) {
+		args->pitch = min_pitch;
+		args->size = args->pitch * args->height;
+	} else {
+		/* ensure sane minimum values */
+		if (args->pitch < min_pitch)
+			args->pitch = min_pitch;
+		if (args->size < args->pitch * args->height)
+			args->size = args->pitch * args->height;
+	}
+
+	shmem = drm_gem_shmem_create_with_handle(file, dev, args->size, &args->handle);
+
+	return PTR_ERR_OR_ZERO(shmem);
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_dumb_create);
+
+static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct drm_gem_object *obj = vma->vm_private_data;
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+	loff_t num_pages = obj->size >> PAGE_SHIFT;
+	struct page *page;
+
+	if (vmf->pgoff > num_pages || WARN_ON_ONCE(!shmem->pages))
+		return VM_FAULT_SIGBUS;
+
+	page = shmem->pages[vmf->pgoff];
+
+	return vmf_insert_page(vma, vmf->address, page);
+}
+
+static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
+{
+	struct drm_gem_object *obj = vma->vm_private_data;
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+	int ret;
+
+	ret = drm_gem_shmem_get_pages(shmem);
+	WARN_ON_ONCE(ret != 0);
+
+	drm_gem_vm_open(vma);
+}
+
+static void drm_gem_shmem_vm_close(struct vm_area_struct *vma)
+{
+	struct drm_gem_object *obj = vma->vm_private_data;
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	drm_gem_shmem_put_pages(shmem);
+	drm_gem_vm_close(vma);
+}
+
+const struct vm_operations_struct drm_gem_shmem_vm_ops = {
+	.fault = drm_gem_shmem_fault,
+	.open = drm_gem_shmem_vm_open,
+	.close = drm_gem_shmem_vm_close,
+};
+EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops);
+
+/**
+ * drm_gem_shmem_mmap - Memory-map a shmem GEM object
+ * @filp: File object
+ * @vma: VMA for the area to be mapped
+ *
+ * This function implements an augmented version of the GEM DRM file mmap
+ * operation for shmem objects. Drivers which employ the shmem helpers should
+ * use this function as their &file_operations.mmap handler in the DRM device file's
+ * file_operations structure.
+ *
+ * Instead of directly referencing this function, drivers should use the
+ * DEFINE_DRM_GEM_SHMEM_FOPS() macro.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
+ */
+int drm_gem_shmem_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	struct drm_gem_shmem_object *shmem;
+	int ret;
+
+	ret = drm_gem_mmap(filp, vma);
+	if (ret)
+		return ret;
+
+	shmem = to_drm_gem_shmem_obj(vma->vm_private_data);
+
+	ret = drm_gem_shmem_get_pages(shmem);
+	if (ret) {
+		drm_gem_vm_close(vma);
+		return ret;
+	}
+
+	/* VM_PFNMAP was set by drm_gem_mmap() */
+	vma->vm_flags &= ~VM_PFNMAP;
+	vma->vm_flags |= VM_MIXEDMAP;
+
+	/* Remove the fake offset */
+	vma->vm_pgoff -= drm_vma_node_start(&shmem->base.vma_node);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_mmap);
+
+/**
+ * drm_gem_shmem_print_info() - Print &drm_gem_shmem_object info for debugfs
+ * @p: DRM printer
+ * @indent: Tab indentation level
+ * @obj: GEM object
+ */
+void drm_gem_shmem_print_info(struct drm_printer *p, unsigned int indent,
+			      const struct drm_gem_object *obj)
+{
+	const struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count);
+	drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
+	drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
+}
+EXPORT_SYMBOL(drm_gem_shmem_print_info);
+
+/**
+ * drm_gem_shmem_get_sg_table - Provide a scatter/gather table of pinned
+ *                              pages for a shmem GEM object
+ * @obj: GEM object
+ *
+ * This function exports a scatter/gather table suitable for PRIME usage by
+ * calling the standard DMA mapping API.
+ *
+ * Returns:
+ * A pointer to the scatter/gather table of pinned pages or NULL on failure.
+ */
+struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_object *obj)
+{
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+	return drm_prime_pages_to_sg(shmem->pages, obj->size >> PAGE_SHIFT);
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_get_sg_table);
+
+/**
+ * drm_gem_shmem_get_pages_sgt - Pin pages, dma map them, and return a
+ *				 scatter/gather table for a shmem GEM object.
+ * @obj: GEM object
+ *
+ * This function returns a scatter/gather table suitable for driver usage. If
+ * the sg table doesn't exist, the pages are pinned, dma-mapped, and a sg
+ * table created.
+ *
+ * Returns:
+ * A pointer to the scatter/gather table of pinned pages or errno on failure.
+ */
+struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_object *obj)
+{
+	int ret;
+	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+	struct sg_table *sgt;
+
+	if (shmem->sgt)
+		return shmem->sgt;
+
+	WARN_ON(obj->import_attach);
+
+	ret = drm_gem_shmem_get_pages(shmem);
+	if (ret)
+		return ERR_PTR(ret);
+
+	sgt = drm_gem_shmem_get_sg_table(&shmem->base);
+	if (IS_ERR(sgt)) {
+		ret = PTR_ERR(sgt);
+		goto err_put_pages;
+	}
+	/* Map the pages for use by the h/w. */
+	dma_map_sg(obj->dev->dev, sgt->sgl, sgt->nents, DMA_BIDIRECTIONAL);
+
+	shmem->sgt = sgt;
+
+	return sgt;
+
+err_put_pages:
+	drm_gem_shmem_put_pages(shmem);
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_get_pages_sgt);
+
+/**
+ * drm_gem_shmem_prime_import_sg_table - Produce a shmem GEM object from
+ *                 another driver's scatter/gather table of pinned pages
+ * @dev: Device to import into
+ * @attach: DMA-BUF attachment
+ * @sgt: Scatter/gather table of pinned pages
+ *
+ * This function imports a scatter/gather table exported via DMA-BUF by
+ * another driver. Drivers that use the shmem helpers should set this as their
+ * &drm_driver.gem_prime_import_sg_table callback.
+ *
+ * Returns:
+ * A pointer to a newly created GEM object or an ERR_PTR-encoded negative
+ * error code on failure.
+ */
+struct drm_gem_object *
+drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
+				    struct dma_buf_attachment *attach,
+				    struct sg_table *sgt)
+{
+	size_t size = PAGE_ALIGN(attach->dmabuf->size);
+	size_t npages = size >> PAGE_SHIFT;
+	struct drm_gem_shmem_object *shmem;
+	int ret;
+
+	shmem = drm_gem_shmem_create(dev, size);
+	if (IS_ERR(shmem))
+		return ERR_CAST(shmem);
+
+	shmem->pages = kvmalloc_array(npages, sizeof(struct page *), GFP_KERNEL);
+	if (!shmem->pages) {
+		ret = -ENOMEM;
+		goto err_free_gem;
+	}
+
+	ret = drm_prime_sg_to_page_addr_arrays(sgt, shmem->pages, NULL, npages);
+	if (ret < 0)
+		goto err_free_array;
+
+	shmem->sgt = sgt;
+	shmem->pages_use_count = 1; /* Permanently pinned from our point of view */
+
+	DRM_DEBUG_PRIME("size = %zu\n", size);
+
+	return &shmem->base;
+
+err_free_array:
+	kvfree(shmem->pages);
+err_free_gem:
+	drm_gem_object_put_unlocked(&shmem->base);
+
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);

include/drm/drm_gem_shmem_helper.h

+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __DRM_GEM_SHMEM_HELPER_H__
+#define __DRM_GEM_SHMEM_HELPER_H__
+
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/mutex.h>
+
+#include <drm/drm_file.h>
+#include <drm/drm_gem.h>
+#include <drm/drm_ioctl.h>
+#include <drm/drm_prime.h>
+
+struct dma_buf_attachment;
+struct drm_mode_create_dumb;
+struct drm_printer;
+struct sg_table;
+
+/**
+ * struct drm_gem_shmem_object - GEM object backed by shmem
+ */
+struct drm_gem_shmem_object {
+	/**
+	 * @base: Base GEM object
+	 */
+	struct drm_gem_object base;
+
+	/**
+	 * @pages_lock: Protects the page table and use count
+	 */
+	struct mutex pages_lock;
+
+	/**
+	 * @pages: Page table
+	 */
+	struct page **pages;
+
+	/**
+	 * @pages_use_count:
+	 *
+	 * Reference count on the pages table.
+	 * The pages are put when the count reaches zero.
+	 */
+	unsigned int pages_use_count;
+
+	/**
+	 * @pages_mark_dirty_on_put:
+	 *
+	 * Mark pages as dirty when they are put.
+	 */
+	unsigned int pages_mark_dirty_on_put    : 1;
+
+	/**
+	 * @pages_mark_accessed_on_put:
+	 *
+	 * Mark pages as accessed when they are put.
+	 */
+	unsigned int pages_mark_accessed_on_put : 1;
+
+	/**
+	 * @sgt: Scatter/gather table for imported PRIME buffers
+	 */
+	struct sg_table *sgt;
+
+	/**
+	 * @vmap_lock: Protects the vmap address and use count
+	 */
+	struct mutex vmap_lock;
+
+	/**
+	 * @vaddr: Kernel virtual address of the backing memory
+	 */
+	void *vaddr;
+
+	/**
+	 * @vmap_use_count:
+	 *
+	 * Reference count on the virtual address.
+	 * The address are un-mapped when the count reaches zero.
+	 */
+	unsigned int vmap_use_count;
+};
+
+#define to_drm_gem_shmem_obj(obj) \
+	container_of(obj, struct drm_gem_shmem_object, base)
+
+/**
+ * DEFINE_DRM_GEM_SHMEM_FOPS() - Macro to generate file operations for shmem drivers
+ * @name: name for the generated structure
+ *
+ * This macro autogenerates a suitable &struct file_operations for shmem based
+ * drivers, which can be assigned to &drm_driver.fops. Note that this structure
+ * cannot be shared between drivers, because it contains a reference to the
+ * current module using THIS_MODULE.
+ *
+ * Note that the declaration is already marked as static - if you need a
+ * non-static version of this you're probably doing it wrong and will break the
+ * THIS_MODULE reference by accident.
+ */
+#define DEFINE_DRM_GEM_SHMEM_FOPS(name) \
+	static const struct file_operations name = {\
+		.owner		= THIS_MODULE,\
+		.open		= drm_open,\
+		.release	= drm_release,\
+		.unlocked_ioctl	= drm_ioctl,\
+		.compat_ioctl	= drm_compat_ioctl,\
+		.poll		= drm_poll,\
+		.read		= drm_read,\
+		.llseek		= noop_llseek,\
+		.mmap		= drm_gem_shmem_mmap, \
+	}
+
+struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size);
+void drm_gem_shmem_free_object(struct drm_gem_object *obj);
+
+int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem);
+void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem);
+int drm_gem_shmem_pin(struct drm_gem_object *obj);
+void drm_gem_shmem_unpin(struct drm_gem_object *obj);
+void *drm_gem_shmem_vmap(struct drm_gem_object *obj);
+void drm_gem_shmem_vunmap(struct drm_gem_object *obj, void *vaddr);
+
+struct drm_gem_shmem_object *
+drm_gem_shmem_create_with_handle(struct drm_file *file_priv,
+				 struct drm_device *dev, size_t size,
+				 uint32_t *handle);
+int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
+			      struct drm_mode_create_dumb *args);
+
+int drm_gem_shmem_mmap(struct file *filp, struct vm_area_struct *vma);
+
+extern const struct vm_operations_struct drm_gem_shmem_vm_ops;
+
+void drm_gem_shmem_print_info(struct drm_printer *p, unsigned int indent,
+			      const struct drm_gem_object *obj);
+
+struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_object *obj);
+struct drm_gem_object *
+drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
+				    struct dma_buf_attachment *attach,
+				    struct sg_table *sgt);
+
+struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_object *obj);
+
+/**
+ * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
+ *
+ * This macro provides a shortcut for setting the shmem GEM operations in
+ * the &drm_driver structure.
+ */
+#define DRM_GEM_SHMEM_DRIVER_OPS \
+	.prime_handle_to_fd	= drm_gem_prime_handle_to_fd, \
+	.prime_fd_to_handle	= drm_gem_prime_fd_to_handle, \
+	.gem_prime_import_sg_table = drm_gem_shmem_prime_import_sg_table, \
+	.gem_prime_mmap		= drm_gem_prime_mmap, \
+	.dumb_create		= drm_gem_shmem_dumb_create
+
+#endif /* __DRM_GEM_SHMEM_HELPER_H__ */