[v7] Add udmabuf misc device
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Message ID 20180827093444.23623-1-kraxel@redhat.com
State New
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Series
  • [v7] Add udmabuf misc device
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Commit Message

Gerd Hoffmann Aug. 27, 2018, 9:34 a.m. UTC
A driver to let userspace turn memfd regions into dma-bufs.

Use case:  Allows qemu create dmabufs for the vga framebuffer or
virtio-gpu ressources.  Then they can be passed around to display
those guest things on the host.  To spice client for classic full
framebuffer display, and hopefully some day to wayland server for
seamless guest window display.

qemu test branch:
  https://git.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf

Cc: David Airlie <airlied@linux.ie>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 Documentation/ioctl/ioctl-number.txt              |   1 +
 include/uapi/linux/udmabuf.h                      |  33 +++
 drivers/dma-buf/udmabuf.c                         | 287 ++++++++++++++++++++++
 tools/testing/selftests/drivers/dma-buf/udmabuf.c |  96 ++++++++
 MAINTAINERS                                       |  16 ++
 drivers/dma-buf/Kconfig                           |   8 +
 drivers/dma-buf/Makefile                          |   1 +
 tools/testing/selftests/drivers/dma-buf/Makefile  |   5 +
 8 files changed, 447 insertions(+)
 create mode 100644 include/uapi/linux/udmabuf.h
 create mode 100644 drivers/dma-buf/udmabuf.c
 create mode 100644 tools/testing/selftests/drivers/dma-buf/udmabuf.c
 create mode 100644 tools/testing/selftests/drivers/dma-buf/Makefile

Comments

Daniel Vetter Aug. 31, 2018, 8:48 a.m. UTC | #1
On Mon, Aug 27, 2018 at 11:34:44AM +0200, Gerd Hoffmann wrote:
> A driver to let userspace turn memfd regions into dma-bufs.
> 
> Use case:  Allows qemu create dmabufs for the vga framebuffer or
> virtio-gpu ressources.  Then they can be passed around to display
> those guest things on the host.  To spice client for classic full
> framebuffer display, and hopefully some day to wayland server for
> seamless guest window display.
> 
> qemu test branch:
>   https://git.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf
> 
> Cc: David Airlie <airlied@linux.ie>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  Documentation/ioctl/ioctl-number.txt              |   1 +
>  include/uapi/linux/udmabuf.h                      |  33 +++
>  drivers/dma-buf/udmabuf.c                         | 287 ++++++++++++++++++++++
>  tools/testing/selftests/drivers/dma-buf/udmabuf.c |  96 ++++++++
>  MAINTAINERS                                       |  16 ++
>  drivers/dma-buf/Kconfig                           |   8 +
>  drivers/dma-buf/Makefile                          |   1 +
>  tools/testing/selftests/drivers/dma-buf/Makefile  |   5 +
>  8 files changed, 447 insertions(+)
>  create mode 100644 include/uapi/linux/udmabuf.h
>  create mode 100644 drivers/dma-buf/udmabuf.c
>  create mode 100644 tools/testing/selftests/drivers/dma-buf/udmabuf.c
>  create mode 100644 tools/testing/selftests/drivers/dma-buf/Makefile
> 
> diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
> index 13a7c999c0..f2ac672eb7 100644
> --- a/Documentation/ioctl/ioctl-number.txt
> +++ b/Documentation/ioctl/ioctl-number.txt
> @@ -272,6 +272,7 @@ Code  Seq#(hex)	Include File		Comments
>  't'	90-91	linux/toshiba.h		toshiba and toshiba_acpi SMM
>  'u'	00-1F	linux/smb_fs.h		gone
>  'u'	20-3F	linux/uvcvideo.h	USB video class host driver
> +'u'	40-4f	linux/udmabuf.h		userspace dma-buf misc device
>  'v'	00-1F	linux/ext2_fs.h		conflict!
>  'v'	00-1F	linux/fs.h		conflict!
>  'v'	00-0F	linux/sonypi.h		conflict!
> diff --git a/include/uapi/linux/udmabuf.h b/include/uapi/linux/udmabuf.h
> new file mode 100644
> index 0000000000..46b6532ed8
> --- /dev/null
> +++ b/include/uapi/linux/udmabuf.h
> @@ -0,0 +1,33 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _UAPI_LINUX_UDMABUF_H
> +#define _UAPI_LINUX_UDMABUF_H
> +
> +#include <linux/types.h>
> +#include <linux/ioctl.h>
> +
> +#define UDMABUF_FLAGS_CLOEXEC	0x01
> +
> +struct udmabuf_create {
> +	__u32 memfd;
> +	__u32 flags;
> +	__u64 offset;
> +	__u64 size;
> +};
> +
> +struct udmabuf_create_item {
> +	__u32 memfd;
> +	__u32 __pad;
> +	__u64 offset;
> +	__u64 size;
> +};
> +
> +struct udmabuf_create_list {
> +	__u32 flags;
> +	__u32 count;
> +	struct udmabuf_create_item list[];
> +};
> +
> +#define UDMABUF_CREATE       _IOW('u', 0x42, struct udmabuf_create)
> +#define UDMABUF_CREATE_LIST  _IOW('u', 0x43, struct udmabuf_create_list)
> +
> +#endif /* _UAPI_LINUX_UDMABUF_H */
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> new file mode 100644
> index 0000000000..8e24204526
> --- /dev/null
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -0,0 +1,287 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/miscdevice.h>
> +#include <linux/dma-buf.h>
> +#include <linux/highmem.h>
> +#include <linux/cred.h>
> +#include <linux/shmem_fs.h>
> +#include <linux/memfd.h>
> +
> +#include <uapi/linux/udmabuf.h>
> +
> +struct udmabuf {
> +	u32 pagecount;
> +	struct page **pages;
> +};
> +
> +static int udmabuf_vm_fault(struct vm_fault *vmf)
> +{
> +	struct vm_area_struct *vma = vmf->vma;
> +	struct udmabuf *ubuf = vma->vm_private_data;
> +
> +	if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
> +		return VM_FAULT_SIGBUS;
> +
> +	vmf->page = ubuf->pages[vmf->pgoff];
> +	get_page(vmf->page);
> +	return 0;
> +}
> +
> +static const struct vm_operations_struct udmabuf_vm_ops = {
> +	.fault = udmabuf_vm_fault,
> +};
> +
> +static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +
> +	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
> +		return -EINVAL;
> +
> +	vma->vm_ops = &udmabuf_vm_ops;
> +	vma->vm_private_data = ubuf;
> +	return 0;
> +}
> +
> +static struct sg_table *map_udmabuf(struct dma_buf_attachment *at,
> +				    enum dma_data_direction direction)
> +{
> +	struct udmabuf *ubuf = at->dmabuf->priv;
> +	struct sg_table *sg;
> +
> +	sg = kzalloc(sizeof(*sg), GFP_KERNEL);
> +	if (!sg)
> +		goto err1;
> +	if (sg_alloc_table_from_pages(sg, ubuf->pages, ubuf->pagecount,
> +				      0, ubuf->pagecount << PAGE_SHIFT,
> +				      GFP_KERNEL) < 0)
> +		goto err2;
> +	if (!dma_map_sg(at->dev, sg->sgl, sg->nents, direction))
> +		goto err3;
> +
> +	return sg;
> +
> +err3:
> +	sg_free_table(sg);
> +err2:
> +	kfree(sg);
> +err1:
> +	return ERR_PTR(-ENOMEM);
> +}
> +
> +static void unmap_udmabuf(struct dma_buf_attachment *at,
> +			  struct sg_table *sg,
> +			  enum dma_data_direction direction)
> +{
> +	sg_free_table(sg);
> +	kfree(sg);
> +}
> +
> +static void release_udmabuf(struct dma_buf *buf)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +	pgoff_t pg;
> +
> +	for (pg = 0; pg < ubuf->pagecount; pg++)
> +		put_page(ubuf->pages[pg]);
> +	kfree(ubuf->pages);
> +	kfree(ubuf);
> +}
> +
> +static void *kmap_udmabuf(struct dma_buf *buf, unsigned long page_num)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +	struct page *page = ubuf->pages[page_num];
> +
> +	return kmap(page);
> +}
> +
> +static void kunmap_udmabuf(struct dma_buf *buf, unsigned long page_num,
> +			   void *vaddr)
> +{
> +	kunmap(vaddr);
> +}
> +
> +static struct dma_buf_ops udmabuf_ops = {
> +	.map_dma_buf	  = map_udmabuf,
> +	.unmap_dma_buf	  = unmap_udmabuf,
> +	.release	  = release_udmabuf,
> +	.map		  = kmap_udmabuf,
> +	.unmap		  = kunmap_udmabuf,
> +	.mmap		  = mmap_udmabuf,
> +};
> +
> +#define SEALS_WANTED (F_SEAL_SHRINK)
> +#define SEALS_DENIED (F_SEAL_WRITE)
> +
> +static long udmabuf_create(struct udmabuf_create_list *head,
> +			   struct udmabuf_create_item *list)
> +{
> +	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> +	struct file *memfd = NULL;
> +	struct udmabuf *ubuf;
> +	struct dma_buf *buf;
> +	pgoff_t pgoff, pgcnt, pgidx, pgbuf;
> +	struct page *page;
> +	int seals, ret = -EINVAL;
> +	u32 i, flags;
> +
> +	ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
> +	if (!ubuf)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < head->count; i++) {
> +		if (!IS_ALIGNED(list[i].offset, PAGE_SIZE))
> +			goto err_free_ubuf;
> +		if (!IS_ALIGNED(list[i].size, PAGE_SIZE))
> +			goto err_free_ubuf;
> +		ubuf->pagecount += list[i].size >> PAGE_SHIFT;
> +	}
> +	ubuf->pages = kmalloc_array(ubuf->pagecount, sizeof(struct page *),
> +				    GFP_KERNEL);
> +	if (!ubuf->pages) {
> +		ret = -ENOMEM;
> +		goto err_free_ubuf;
> +	}
> +
> +	pgbuf = 0;
> +	for (i = 0; i < head->count; i++) {
> +		memfd = fget(list[i].memfd);
> +		if (!memfd)
> +			goto err_put_pages;
> +		if (!shmem_mapping(file_inode(memfd)->i_mapping))
> +			goto err_put_pages;
> +		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
> +		if (seals == -EINVAL ||
> +		    (seals & SEALS_WANTED) != SEALS_WANTED ||
> +		    (seals & SEALS_DENIED) != 0)
> +			goto err_put_pages;
> +		pgoff = list[i].offset >> PAGE_SHIFT;
> +		pgcnt = list[i].size   >> PAGE_SHIFT;
> +		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
> +			page = shmem_read_mapping_page(
> +				file_inode(memfd)->i_mapping, pgoff + pgidx);
> +			if (IS_ERR(page)) {
> +				ret = PTR_ERR(page);
> +				goto err_put_pages;
> +			}
> +			ubuf->pages[pgbuf++] = page;
> +		}
> +		fput(memfd);
> +	}
> +	memfd = NULL;
> +
> +	exp_info.ops  = &udmabuf_ops;
> +	exp_info.size = ubuf->pagecount << PAGE_SHIFT;
> +	exp_info.priv = ubuf;
> +
> +	buf = dma_buf_export(&exp_info);
> +	if (IS_ERR(buf)) {
> +		ret = PTR_ERR(buf);
> +		goto err_put_pages;
> +	}
> +
> +	flags = 0;
> +	if (head->flags & UDMABUF_FLAGS_CLOEXEC)
> +		flags |= O_CLOEXEC;
> +	return dma_buf_fd(buf, flags);
> +
> +err_put_pages:
> +	while (pgbuf > 0)
> +		put_page(ubuf->pages[--pgbuf]);
> +err_free_ubuf:
> +	fput(memfd);
> +	kfree(ubuf->pages);
> +	kfree(ubuf);
> +	return ret;
> +}
> +
> +static long udmabuf_ioctl_create(struct file *filp, unsigned long arg)
> +{
> +	struct udmabuf_create create;
> +	struct udmabuf_create_list head;
> +	struct udmabuf_create_item list;
> +
> +	if (copy_from_user(&create, (void __user *)arg,
> +			   sizeof(struct udmabuf_create)))
> +		return -EFAULT;
> +
> +	head.flags  = create.flags;
> +	head.count  = 1;
> +	list.memfd  = create.memfd;
> +	list.offset = create.offset;
> +	list.size   = create.size;
> +
> +	return udmabuf_create(&head, &list);
> +}
> +
> +static long udmabuf_ioctl_create_list(struct file *filp, unsigned long arg)
> +{
> +	struct udmabuf_create_list head;
> +	struct udmabuf_create_item *list;
> +	int ret = -EINVAL;
> +	u32 lsize;
> +
> +	if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
> +		return -EFAULT;
> +	if (head.count > 1024)
> +		return -EINVAL;
> +	lsize = sizeof(struct udmabuf_create_item) * head.count;
> +	list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
> +	if (IS_ERR(list))
> +		return PTR_ERR(list);
> +
> +	ret = udmabuf_create(&head, list);
> +	kfree(list);
> +	return ret;
> +}
> +
> +static long udmabuf_ioctl(struct file *filp, unsigned int ioctl,
> +			  unsigned long arg)
> +{
> +	long ret;
> +
> +	switch (ioctl) {
> +	case UDMABUF_CREATE:
> +		ret = udmabuf_ioctl_create(filp, arg);
> +		break;
> +	case UDMABUF_CREATE_LIST:
> +		ret = udmabuf_ioctl_create_list(filp, arg);
> +		break;
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +	return ret;
> +}
> +
> +static const struct file_operations udmabuf_fops = {
> +	.owner		= THIS_MODULE,
> +	.unlocked_ioctl = udmabuf_ioctl,
> +};
> +
> +static struct miscdevice udmabuf_misc = {
> +	.minor          = MISC_DYNAMIC_MINOR,
> +	.name           = "udmabuf",
> +	.fops           = &udmabuf_fops,
> +};
> +
> +static int __init udmabuf_dev_init(void)
> +{
> +	return misc_register(&udmabuf_misc);
> +}
> +
> +static void __exit udmabuf_dev_exit(void)
> +{
> +	misc_deregister(&udmabuf_misc);
> +}
> +
> +module_init(udmabuf_dev_init)
> +module_exit(udmabuf_dev_exit)
> +
> +MODULE_AUTHOR("Gerd Hoffmann <kraxel@redhat.com>");
> +MODULE_LICENSE("GPL v2");
> diff --git a/tools/testing/selftests/drivers/dma-buf/udmabuf.c b/tools/testing/selftests/drivers/dma-buf/udmabuf.c
> new file mode 100644
> index 0000000000..376b1d6730
> --- /dev/null
> +++ b/tools/testing/selftests/drivers/dma-buf/udmabuf.c
> @@ -0,0 +1,96 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include <string.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <malloc.h>
> +
> +#include <sys/ioctl.h>
> +#include <sys/syscall.h>
> +#include <linux/memfd.h>
> +#include <linux/udmabuf.h>
> +
> +#define TEST_PREFIX	"drivers/dma-buf/udmabuf"
> +#define NUM_PAGES       4
> +
> +static int memfd_create(const char *name, unsigned int flags)
> +{
> +	return syscall(__NR_memfd_create, name, flags);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	struct udmabuf_create create;
> +	int devfd, memfd, buf, ret;
> +	off_t size;
> +	void *mem;
> +
> +	devfd = open("/dev/udmabuf", O_RDWR);
> +	if (devfd < 0) {
> +		printf("%s: [skip,no-udmabuf]\n", TEST_PREFIX);
> +		exit(77);
> +	}
> +
> +	memfd = memfd_create("udmabuf-test", MFD_CLOEXEC);
> +	if (memfd < 0) {
> +		printf("%s: [skip,no-memfd]\n", TEST_PREFIX);
> +		exit(77);
> +	}
> +
> +	size = getpagesize() * NUM_PAGES;
> +	ret = ftruncate(memfd, size);
> +	if (ret == -1) {
> +		printf("%s: [FAIL,memfd-truncate]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	memset(&create, 0, sizeof(create));
> +
> +	/* should fail (offset not page aligned) */
> +	create.memfd  = memfd;
> +	create.offset = getpagesize()/2;
> +	create.size   = getpagesize();
> +	buf = ioctl(devfd, UDMABUF_CREATE, &create);
> +	if (buf >= 0) {
> +		printf("%s: [FAIL,test-1]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	/* should fail (size not multiple of page) */
> +	create.memfd  = memfd;
> +	create.offset = 0;
> +	create.size   = getpagesize()/2;
> +	buf = ioctl(devfd, UDMABUF_CREATE, &create);
> +	if (buf >= 0) {
> +		printf("%s: [FAIL,test-2]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	/* should fail (not memfd) */
> +	create.memfd  = 0; /* stdin */
> +	create.offset = 0;
> +	create.size   = size;
> +	buf = ioctl(devfd, UDMABUF_CREATE, &create);
> +	if (buf >= 0) {
> +		printf("%s: [FAIL,test-3]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	/* should work */
> +	create.memfd  = memfd;
> +	create.offset = 0;
> +	create.size   = size;
> +	buf = ioctl(devfd, UDMABUF_CREATE, &create);
> +	if (buf < 0) {
> +		printf("%s: [FAIL,test-4]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	fprintf(stderr, "%s: ok\n", TEST_PREFIX);
> +	close(buf);
> +	close(memfd);
> +	close(devfd);
> +	return 0;
> +}
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a5b256b259..11a9b04277 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -14934,6 +14934,14 @@ S:	Maintained
>  F:	Documentation/filesystems/udf.txt
>  F:	fs/udf/
>  
> +UDMABUF DRIVER
> +M:	Gerd Hoffmann <kraxel@redhat.com>
> +L:	dri-devel@lists.freedesktop.org
> +S:	Maintained
> +F:	drivers/dma-buf/udmabuf.c
> +F:	include/uapi/linux/udmabuf.h
> +F:	tools/testing/selftests/drivers/dma-buf/udmabuf.c

Dupe, remove this one (since only the 2nd one has the drm-misc git repo
entry).

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> +
>  UDRAW TABLET
>  M:	Bastien Nocera <hadess@hadess.net>
>  L:	linux-input@vger.kernel.org
> @@ -15343,6 +15351,14 @@ F:	arch/x86/um/
>  F:	fs/hostfs/
>  F:	fs/hppfs/
>  
> +USERSPACE DMA BUFFER DRIVER
> +M:	Gerd Hoffmann <kraxel@redhat.com>
> +S:	Maintained
> +L:	dri-devel@lists.freedesktop.org
> +F:	drivers/dma-buf/udmabuf.c
> +F:	include/uapi/linux/udmabuf.h
> +T:	git git://anongit.freedesktop.org/drm/drm-misc
> +
>  USERSPACE I/O (UIO)
>  M:	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>  S:	Maintained
> diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> index ed3b785bae..338129eb12 100644
> --- a/drivers/dma-buf/Kconfig
> +++ b/drivers/dma-buf/Kconfig
> @@ -30,4 +30,12 @@ config SW_SYNC
>  	  WARNING: improper use of this can result in deadlocking kernel
>  	  drivers from userspace. Intended for test and debug only.
>  
> +config UDMABUF
> +	bool "userspace dmabuf misc driver"
> +	default n
> +	depends on DMA_SHARED_BUFFER
> +	help
> +	  A driver to let userspace turn memfd regions into dma-bufs.
> +	  Qemu can use this to create host dmabufs for guest framebuffers.
> +
>  endmenu
> diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
> index c33bf88631..0913a6ccab 100644
> --- a/drivers/dma-buf/Makefile
> +++ b/drivers/dma-buf/Makefile
> @@ -1,3 +1,4 @@
>  obj-y := dma-buf.o dma-fence.o dma-fence-array.o reservation.o seqno-fence.o
>  obj-$(CONFIG_SYNC_FILE)		+= sync_file.o
>  obj-$(CONFIG_SW_SYNC)		+= sw_sync.o sync_debug.o
> +obj-$(CONFIG_UDMABUF)		+= udmabuf.o
> diff --git a/tools/testing/selftests/drivers/dma-buf/Makefile b/tools/testing/selftests/drivers/dma-buf/Makefile
> new file mode 100644
> index 0000000000..4154c3d7aa
> --- /dev/null
> +++ b/tools/testing/selftests/drivers/dma-buf/Makefile
> @@ -0,0 +1,5 @@
> +CFLAGS += -I../../../../../usr/include/
> +
> +TEST_GEN_PROGS := udmabuf
> +
> +include ../../lib.mk
> -- 
> 2.9.3
>
Laurent Pinchart Sept. 10, 2018, 12:12 p.m. UTC | #2
Hi Gerd,

Thank you for the patch.

CC'ing the linux-api mailing list as this creates a new userspace API.

On Monday, 27 August 2018 12:34:44 EEST Gerd Hoffmann wrote:
> A driver to let userspace turn memfd regions into dma-bufs.
> 
> Use case:  Allows qemu create dmabufs for the vga framebuffer or
> virtio-gpu ressources.  Then they can be passed around to display
> those guest things on the host.  To spice client for classic full
> framebuffer display, and hopefully some day to wayland server for
> seamless guest window display.
> 
> qemu test branch:
>   https://git.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf
> 
> Cc: David Airlie <airlied@linux.ie>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  Documentation/ioctl/ioctl-number.txt              |   1 +
>  include/uapi/linux/udmabuf.h                      |  33 +++
>  drivers/dma-buf/udmabuf.c                         | 287 +++++++++++++++++++
>  tools/testing/selftests/drivers/dma-buf/udmabuf.c |  96 ++++++++
>  MAINTAINERS                                       |  16 ++
>  drivers/dma-buf/Kconfig                           |   8 +
>  drivers/dma-buf/Makefile                          |   1 +
>  tools/testing/selftests/drivers/dma-buf/Makefile  |   5 +
>  8 files changed, 447 insertions(+)
>  create mode 100644 include/uapi/linux/udmabuf.h
>  create mode 100644 drivers/dma-buf/udmabuf.c
>  create mode 100644 tools/testing/selftests/drivers/dma-buf/udmabuf.c
>  create mode 100644 tools/testing/selftests/drivers/dma-buf/Makefile

[snip]

> diff --git a/include/uapi/linux/udmabuf.h b/include/uapi/linux/udmabuf.h
> new file mode 100644
> index 0000000000..46b6532ed8
> --- /dev/null
> +++ b/include/uapi/linux/udmabuf.h
> @@ -0,0 +1,33 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _UAPI_LINUX_UDMABUF_H
> +#define _UAPI_LINUX_UDMABUF_H
> +
> +#include <linux/types.h>
> +#include <linux/ioctl.h>
> +
> +#define UDMABUF_FLAGS_CLOEXEC	0x01
> +
> +struct udmabuf_create {
> +	__u32 memfd;
> +	__u32 flags;
> +	__u64 offset;
> +	__u64 size;
> +};
> +
> +struct udmabuf_create_item {
> +	__u32 memfd;
> +	__u32 __pad;
> +	__u64 offset;
> +	__u64 size;
> +};
> +
> +struct udmabuf_create_list {
> +	__u32 flags;
> +	__u32 count;
> +	struct udmabuf_create_item list[];
> +};
> +
> +#define UDMABUF_CREATE       _IOW('u', 0x42, struct udmabuf_create)

Why do you start at 0x42 if you reserve the 0x40-0x4f range ?

> +#define UDMABUF_CREATE_LIST  _IOW('u', 0x43, struct udmabuf_create_list)

Where's the documentation ? :-)

> +#endif /* _UAPI_LINUX_UDMABUF_H */
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> new file mode 100644
> index 0000000000..8e24204526
> --- /dev/null
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -0,0 +1,287 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/init.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/miscdevice.h>
> +#include <linux/dma-buf.h>
> +#include <linux/highmem.h>
> +#include <linux/cred.h>
> +#include <linux/shmem_fs.h>
> +#include <linux/memfd.h>

Could you please keep the #include alphabetically sorted ? It helps locating 
duplicates.

> +#include <uapi/linux/udmabuf.h>

I think you can just #include <linux/udmabuf.h>, no need to use the uapi/ 
prefix.

> +struct udmabuf {
> +	u32 pagecount;
> +	struct page **pages;
> +};
> +
> +static int udmabuf_vm_fault(struct vm_fault *vmf)
> +{
> +	struct vm_area_struct *vma = vmf->vma;
> +	struct udmabuf *ubuf = vma->vm_private_data;
> +
> +	if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
> +		return VM_FAULT_SIGBUS;

Just curious, when do you expect this to happen ?

> +	vmf->page = ubuf->pages[vmf->pgoff];
> +	get_page(vmf->page);
> +	return 0;
> +}
> +
> +static const struct vm_operations_struct udmabuf_vm_ops = {
> +	.fault = udmabuf_vm_fault,
> +};
> +
> +static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +
> +	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
> +		return -EINVAL;
> +
> +	vma->vm_ops = &udmabuf_vm_ops;
> +	vma->vm_private_data = ubuf;
> +	return 0;
> +}
> +
> +static struct sg_table *map_udmabuf(struct dma_buf_attachment *at,
> +				    enum dma_data_direction direction)
> +{
> +	struct udmabuf *ubuf = at->dmabuf->priv;
> +	struct sg_table *sg;
> +
> +	sg = kzalloc(sizeof(*sg), GFP_KERNEL);
> +	if (!sg)
> +		goto err1;

You can return ERR_PTR(-ENOMEM) directly.

> +	if (sg_alloc_table_from_pages(sg, ubuf->pages, ubuf->pagecount,
> +				      0, ubuf->pagecount << PAGE_SHIFT,
> +				      GFP_KERNEL) < 0)

Shouldn't you propagate the return value from sg_alloc_table_from_pages() ?

> +		goto err2;
> +	if (!dma_map_sg(at->dev, sg->sgl, sg->nents, direction))
> +		goto err3;
> +
> +	return sg;
> +
> +err3:
> +	sg_free_table(sg);
> +err2:
> +	kfree(sg);
> +err1:
> +	return ERR_PTR(-ENOMEM);

You can merge all these labels with

error:
	if (sg) {
		sg_free_table(sg);
		kfree(sg);
	}

	return ERR_PTR(-ENOMEM);

> +}
> +
> +static void unmap_udmabuf(struct dma_buf_attachment *at,
> +			  struct sg_table *sg,
> +			  enum dma_data_direction direction)
> +{
> +	sg_free_table(sg);
> +	kfree(sg);
> +}
> +
> +static void release_udmabuf(struct dma_buf *buf)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +	pgoff_t pg;
> +
> +	for (pg = 0; pg < ubuf->pagecount; pg++)

Shouldn't both pg and pagecount have the same type ? Why does the loop counter 
qualify for a pgoff_t and not the pagecount field ? Granted, the pgoff_t is 
documented as "The type of an index in the page cache", so pagecount doesn't 
really quality, but the fact that one is an unsigned long and the other a u32 
makes me think that something is wrong.

> +		put_page(ubuf->pages[pg]);
> +	kfree(ubuf->pages);
> +	kfree(ubuf);
> +}
> +
> +static void *kmap_udmabuf(struct dma_buf *buf, unsigned long page_num)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +	struct page *page = ubuf->pages[page_num];
> +
> +	return kmap(page);
> +}
> +
> +static void kunmap_udmabuf(struct dma_buf *buf, unsigned long page_num,
> +			   void *vaddr)
> +{
> +	kunmap(vaddr);
> +}
> +
> +static struct dma_buf_ops udmabuf_ops = {

static const struct

> +	.map_dma_buf	  = map_udmabuf,
> +	.unmap_dma_buf	  = unmap_udmabuf,
> +	.release	  = release_udmabuf,
> +	.map		  = kmap_udmabuf,
> +	.unmap		  = kunmap_udmabuf,
> +	.mmap		  = mmap_udmabuf,
> +};
> +
> +#define SEALS_WANTED (F_SEAL_SHRINK)
> +#define SEALS_DENIED (F_SEAL_WRITE)
> +
> +static long udmabuf_create(struct udmabuf_create_list *head,
> +			   struct udmabuf_create_item *list)

Those two structures are not modified by the function, you can make them 
const.

> +{
> +	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> +	struct file *memfd = NULL;
> +	struct udmabuf *ubuf;
> +	struct dma_buf *buf;
> +	pgoff_t pgoff, pgcnt, pgidx, pgbuf;
> +	struct page *page;
> +	int seals, ret = -EINVAL;
> +	u32 i, flags;
> +
> +	ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);

sizeof(*ubuf)

> +	if (!ubuf)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < head->count; i++) {
> +		if (!IS_ALIGNED(list[i].offset, PAGE_SIZE))
> +			goto err_free_ubuf;
> +		if (!IS_ALIGNED(list[i].size, PAGE_SIZE))
> +			goto err_free_ubuf;
> +		ubuf->pagecount += list[i].size >> PAGE_SHIFT;

Is there a risk of overflowing pagecount ?

> +	}
> +	ubuf->pages = kmalloc_array(ubuf->pagecount, sizeof(struct page *),
> +				    GFP_KERNEL);

sizeof(*ubuf->pages)

> +	if (!ubuf->pages) {
> +		ret = -ENOMEM;
> +		goto err_free_ubuf;
> +	}
> +
> +	pgbuf = 0;
> +	for (i = 0; i < head->count; i++) {
> +		memfd = fget(list[i].memfd);
> +		if (!memfd)
> +			goto err_put_pages;
> +		if (!shmem_mapping(file_inode(memfd)->i_mapping))
> +			goto err_put_pages;
> +		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
> +		if (seals == -EINVAL ||
> +		    (seals & SEALS_WANTED) != SEALS_WANTED ||
> +		    (seals & SEALS_DENIED) != 0)
> +			goto err_put_pages;

All these conditions will return -EINVAL. I'm not familiar with the memfd API, 
should some error conditions return a different error code to make them 
distinguishable by userspace ?

> +		pgoff = list[i].offset >> PAGE_SHIFT;
> +		pgcnt = list[i].size   >> PAGE_SHIFT;
> +		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
> +			page = shmem_read_mapping_page(
> +				file_inode(memfd)->i_mapping, pgoff + pgidx);

Can't pgoff + pgcnt overflow the total number of avialble pages ?

> +			if (IS_ERR(page)) {
> +				ret = PTR_ERR(page);
> +				goto err_put_pages;
> +			}
> +			ubuf->pages[pgbuf++] = page;
> +		}
> +		fput(memfd);
> +	}
> +	memfd = NULL;

I'd move this line just after fput(memfd) inside the loop to avoid 
introduction bugs in the future if we add code that can break from the loop 
before the fget() call.

> +	exp_info.ops  = &udmabuf_ops;
> +	exp_info.size = ubuf->pagecount << PAGE_SHIFT;
> +	exp_info.priv = ubuf;
> +
> +	buf = dma_buf_export(&exp_info);
> +	if (IS_ERR(buf)) {
> +		ret = PTR_ERR(buf);
> +		goto err_put_pages;
> +	}
> +
> +	flags = 0;
> +	if (head->flags & UDMABUF_FLAGS_CLOEXEC)
> +		flags |= O_CLOEXEC;
> +	return dma_buf_fd(buf, flags);
> +
> +err_put_pages:
> +	while (pgbuf > 0)
> +		put_page(ubuf->pages[--pgbuf]);

If you initialize pgbuf to 0 you can merge the two error labels.

> +err_free_ubuf:
> +	fput(memfd);
> +	kfree(ubuf->pages);
> +	kfree(ubuf);
> +	return ret;
> +}
> +
> +static long udmabuf_ioctl_create(struct file *filp, unsigned long arg)
> +{
> +	struct udmabuf_create create;
> +	struct udmabuf_create_list head;
> +	struct udmabuf_create_item list;
> +
> +	if (copy_from_user(&create, (void __user *)arg,
> +			   sizeof(struct udmabuf_create)))

sizeof(create)

> +		return -EFAULT;
> +
> +	head.flags  = create.flags;
> +	head.count  = 1;
> +	list.memfd  = create.memfd;
> +	list.offset = create.offset;
> +	list.size   = create.size;
> +
> +	return udmabuf_create(&head, &list);
> +}
> +
> +static long udmabuf_ioctl_create_list(struct file *filp, unsigned long arg)
> +{
> +	struct udmabuf_create_list head;
> +	struct udmabuf_create_item *list;
> +	int ret = -EINVAL;
> +	u32 lsize;
> +
> +	if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
> +		return -EFAULT;
> +	if (head.count > 1024)
> +		return -EINVAL;
> +	lsize = sizeof(struct udmabuf_create_item) * head.count;
> +	list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
> +	if (IS_ERR(list))
> +		return PTR_ERR(list);
> +
> +	ret = udmabuf_create(&head, list);
> +	kfree(list);
> +	return ret;
> +}
> +
> +static long udmabuf_ioctl(struct file *filp, unsigned int ioctl,
> +			  unsigned long arg)
> +{
> +	long ret;
> +
> +	switch (ioctl) {
> +	case UDMABUF_CREATE:
> +		ret = udmabuf_ioctl_create(filp, arg);
> +		break;
> +	case UDMABUF_CREATE_LIST:
> +		ret = udmabuf_ioctl_create_list(filp, arg);
> +		break;
> +	default:
> +		ret = -EINVAL;

The proper error code for invalid ioctls is -ENOTTY.

> +		break;
> +	}
> +	return ret;
> +}
> +
> +static const struct file_operations udmabuf_fops = {
> +	.owner		= THIS_MODULE,
> +	.unlocked_ioctl = udmabuf_ioctl,
> +};
> +
> +static struct miscdevice udmabuf_misc = {
> +	.minor          = MISC_DYNAMIC_MINOR,
> +	.name           = "udmabuf",
> +	.fops           = &udmabuf_fops,
> +};
> +
> +static int __init udmabuf_dev_init(void)
> +{
> +	return misc_register(&udmabuf_misc);
> +}
> +
> +static void __exit udmabuf_dev_exit(void)
> +{
> +	misc_deregister(&udmabuf_misc);
> +}
> +
> +module_init(udmabuf_dev_init)
> +module_exit(udmabuf_dev_exit)
> +
> +MODULE_AUTHOR("Gerd Hoffmann <kraxel@redhat.com>");
> +MODULE_LICENSE("GPL v2");
> diff --git a/tools/testing/selftests/drivers/dma-buf/udmabuf.c
> b/tools/testing/selftests/drivers/dma-buf/udmabuf.c new file mode 100644
> index 0000000000..376b1d6730
> --- /dev/null
> +++ b/tools/testing/selftests/drivers/dma-buf/udmabuf.c
> @@ -0,0 +1,96 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include <string.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <malloc.h>
> +
> +#include <sys/ioctl.h>
> +#include <sys/syscall.h>
> +#include <linux/memfd.h>
> +#include <linux/udmabuf.h>
> +
> +#define TEST_PREFIX	"drivers/dma-buf/udmabuf"
> +#define NUM_PAGES       4
> +
> +static int memfd_create(const char *name, unsigned int flags)
> +{
> +	return syscall(__NR_memfd_create, name, flags);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	struct udmabuf_create create;
> +	int devfd, memfd, buf, ret;
> +	off_t size;
> +	void *mem;
> +
> +	devfd = open("/dev/udmabuf", O_RDWR);
> +	if (devfd < 0) {
> +		printf("%s: [skip,no-udmabuf]\n", TEST_PREFIX);
> +		exit(77);
> +	}
> +
> +	memfd = memfd_create("udmabuf-test", MFD_CLOEXEC);
> +	if (memfd < 0) {
> +		printf("%s: [skip,no-memfd]\n", TEST_PREFIX);
> +		exit(77);
> +	}
> +
> +	size = getpagesize() * NUM_PAGES;
> +	ret = ftruncate(memfd, size);
> +	if (ret == -1) {
> +		printf("%s: [FAIL,memfd-truncate]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	memset(&create, 0, sizeof(create));
> +
> +	/* should fail (offset not page aligned) */
> +	create.memfd  = memfd;
> +	create.offset = getpagesize()/2;
> +	create.size   = getpagesize();
> +	buf = ioctl(devfd, UDMABUF_CREATE, &create);
> +	if (buf >= 0) {
> +		printf("%s: [FAIL,test-1]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	/* should fail (size not multiple of page) */
> +	create.memfd  = memfd;
> +	create.offset = 0;
> +	create.size   = getpagesize()/2;
> +	buf = ioctl(devfd, UDMABUF_CREATE, &create);
> +	if (buf >= 0) {
> +		printf("%s: [FAIL,test-2]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	/* should fail (not memfd) */
> +	create.memfd  = 0; /* stdin */
> +	create.offset = 0;
> +	create.size   = size;
> +	buf = ioctl(devfd, UDMABUF_CREATE, &create);
> +	if (buf >= 0) {
> +		printf("%s: [FAIL,test-3]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	/* should work */
> +	create.memfd  = memfd;
> +	create.offset = 0;
> +	create.size   = size;
> +	buf = ioctl(devfd, UDMABUF_CREATE, &create);
> +	if (buf < 0) {
> +		printf("%s: [FAIL,test-4]\n", TEST_PREFIX);
> +		exit(1);
> +	}
> +
> +	fprintf(stderr, "%s: ok\n", TEST_PREFIX);
> +	close(buf);
> +	close(memfd);
> +	close(devfd);
> +	return 0;
> +}
> diff --git a/MAINTAINERS b/MAINTAINERS
> index a5b256b259..11a9b04277 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -14934,6 +14934,14 @@ S:	Maintained
>  F:	Documentation/filesystems/udf.txt
>  F:	fs/udf/
> 
> +UDMABUF DRIVER
> +M:	Gerd Hoffmann <kraxel@redhat.com>
> +L:	dri-devel@lists.freedesktop.org
> +S:	Maintained
> +F:	drivers/dma-buf/udmabuf.c
> +F:	include/uapi/linux/udmabuf.h
> +F:	tools/testing/selftests/drivers/dma-buf/udmabuf.c
> +
>  UDRAW TABLET
>  M:	Bastien Nocera <hadess@hadess.net>
>  L:	linux-input@vger.kernel.org
> @@ -15343,6 +15351,14 @@ F:	arch/x86/um/
>  F:	fs/hostfs/
>  F:	fs/hppfs/
> 
> +USERSPACE DMA BUFFER DRIVER
> +M:	Gerd Hoffmann <kraxel@redhat.com>
> +S:	Maintained
> +L:	dri-devel@lists.freedesktop.org
> +F:	drivers/dma-buf/udmabuf.c
> +F:	include/uapi/linux/udmabuf.h
> +T:	git git://anongit.freedesktop.org/drm/drm-misc

One entry should be enough.

>  USERSPACE I/O (UIO)
>  M:	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>  S:	Maintained

[snip]
Gerd Hoffmann Sept. 11, 2018, 6:50 a.m. UTC | #3
Hi,

> > +#define UDMABUF_CREATE       _IOW('u', 0x42, struct udmabuf_create)
> 
> Why do you start at 0x42 if you reserve the 0x40-0x4f range ?

No particular strong reason, just that using 42 was less boring than
starting with 0x40.

> > +#define UDMABUF_CREATE_LIST  _IOW('u', 0x43, struct udmabuf_create_list)
> 
> Where's the documentation ? :-)

Isn't it simple enough?

But, well, yes, I guess I can add some kerneldoc comments.

> > +static int udmabuf_vm_fault(struct vm_fault *vmf)
> > +{
> > +	struct vm_area_struct *vma = vmf->vma;
> > +	struct udmabuf *ubuf = vma->vm_private_data;
> > +
> > +	if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
> > +		return VM_FAULT_SIGBUS;
> 
> Just curious, when do you expect this to happen ?

It should not.  If it actually happens it would be a bug somewhere,
thats why the WARN_ON.

> > +	struct udmabuf *ubuf;

> > +	ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
> 
> sizeof(*ubuf)

Why?  Should not make a difference ...

> > +		memfd = fget(list[i].memfd);
> > +		if (!memfd)
> > +			goto err_put_pages;
> > +		if (!shmem_mapping(file_inode(memfd)->i_mapping))
> > +			goto err_put_pages;
> > +		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
> > +		if (seals == -EINVAL ||
> > +		    (seals & SEALS_WANTED) != SEALS_WANTED ||
> > +		    (seals & SEALS_DENIED) != 0)
> > +			goto err_put_pages;
> 
> All these conditions will return -EINVAL. I'm not familiar with the memfd API, 
> should some error conditions return a different error code to make them 
> distinguishable by userspace ?

Hmm, I guess EBADFD would be reasonable in case the file handle isn't a
memfd.  Other suggestions?

I'll prepare a fixup patch series addressing most of the other
review comments.

cheers,
  Gerd
Laurent Pinchart Sept. 11, 2018, 9:50 a.m. UTC | #4
Hi Gerd,

On Tuesday, 11 September 2018 09:50:14 EEST Gerd Hoffmann wrote:
>   Hi,
> 
> >> +#define UDMABUF_CREATE       _IOW('u', 0x42, struct udmabuf_create)
> > 
> > Why do you start at 0x42 if you reserve the 0x40-0x4f range ?
> 
> No particular strong reason, just that using 42 was less boring than
> starting with 0x40.
> 
> >> +#define UDMABUF_CREATE_LIST  _IOW('u', 0x43, struct
> >> udmabuf_create_list)
> > 
> > Where's the documentation ? :-)
> 
> Isn't it simple enough?

No kernel UAPI is simple enough to get away without documenting it.

> But, well, yes, I guess I can add some kerneldoc comments.
> 
> >> +static int udmabuf_vm_fault(struct vm_fault *vmf)
> >> +{
> >> +	struct vm_area_struct *vma = vmf->vma;
> >> +	struct udmabuf *ubuf = vma->vm_private_data;
> >> +
> >> +	if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
> >> +		return VM_FAULT_SIGBUS;
> > 
> > Just curious, when do you expect this to happen ?
> 
> It should not.  If it actually happens it would be a bug somewhere,
> thats why the WARN_ON.

But you seem to consider that this condition that should never happen still 
has a high enough chance of happening that it's worth a WARN_ON(). I was 
wondering why this one in particular, and not other conditions that also can't 
happen and are not checked through the code. 

> >> +	struct udmabuf *ubuf;
> >> 
> >> +	ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
> > 
> > sizeof(*ubuf)
> 
> Why?  Should not make a difference ...

Because the day we replace

	struct udmabuf *ubuf;

with

	struct udmabuf_ext *ubuf;

and forget to change the next line, we'll introduce a bug. That's why 
sizeof(variable) is preferred over sizeof(type). Another reason is that I can 
easily see that

	ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL);

is correct, while using sizeof(type) requires me to go and look up the 
declaration of the variable.

> >> +		memfd = fget(list[i].memfd);
> >> +		if (!memfd)
> >> +			goto err_put_pages;
> >> +		if (!shmem_mapping(file_inode(memfd)->i_mapping))
> >> +			goto err_put_pages;
> >> +		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
> >> +		if (seals == -EINVAL ||
> >> +		    (seals & SEALS_WANTED) != SEALS_WANTED ||
> >> +		    (seals & SEALS_DENIED) != 0)
> >> +			goto err_put_pages;
> > 
> > All these conditions will return -EINVAL. I'm not familiar with the memfd
> > API, should some error conditions return a different error code to make
> > them distinguishable by userspace ?
> 
> Hmm, I guess EBADFD would be reasonable in case the file handle isn't a
> memfd.  Other suggestions?

I'll let others comment on this as I don't feel qualified to pick proper error 
codes, not being familiar with the memfd API.

> I'll prepare a fixup patch series addressing most of the other
> review comments.
Daniel Vetter Sept. 11, 2018, 10:05 a.m. UTC | #5
On Tue, Sep 11, 2018 at 11:50 AM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> Hi Gerd,
>
> On Tuesday, 11 September 2018 09:50:14 EEST Gerd Hoffmann wrote:
>>   Hi,
>>
>> >> +#define UDMABUF_CREATE       _IOW('u', 0x42, struct udmabuf_create)
>> >
>> > Why do you start at 0x42 if you reserve the 0x40-0x4f range ?
>>
>> No particular strong reason, just that using 42 was less boring than
>> starting with 0x40.
>>
>> >> +#define UDMABUF_CREATE_LIST  _IOW('u', 0x43, struct
>> >> udmabuf_create_list)
>> >
>> > Where's the documentation ? :-)
>>
>> Isn't it simple enough?
>
> No kernel UAPI is simple enough to get away without documenting it.

Simplest option would be to throw a bit of kerneldoc into the uapi
header, add Documentation/driver-api/dma-buf.rst.
-Daniel

>
>> But, well, yes, I guess I can add some kerneldoc comments.
>>
>> >> +static int udmabuf_vm_fault(struct vm_fault *vmf)
>> >> +{
>> >> +  struct vm_area_struct *vma = vmf->vma;
>> >> +  struct udmabuf *ubuf = vma->vm_private_data;
>> >> +
>> >> +  if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
>> >> +          return VM_FAULT_SIGBUS;
>> >
>> > Just curious, when do you expect this to happen ?
>>
>> It should not.  If it actually happens it would be a bug somewhere,
>> thats why the WARN_ON.
>
> But you seem to consider that this condition that should never happen still
> has a high enough chance of happening that it's worth a WARN_ON(). I was
> wondering why this one in particular, and not other conditions that also can't
> happen and are not checked through the code.
>
>> >> +  struct udmabuf *ubuf;
>> >>
>> >> +  ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
>> >
>> > sizeof(*ubuf)
>>
>> Why?  Should not make a difference ...
>
> Because the day we replace
>
>         struct udmabuf *ubuf;
>
> with
>
>         struct udmabuf_ext *ubuf;
>
> and forget to change the next line, we'll introduce a bug. That's why
> sizeof(variable) is preferred over sizeof(type). Another reason is that I can
> easily see that
>
>         ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL);
>
> is correct, while using sizeof(type) requires me to go and look up the
> declaration of the variable.
>
>> >> +          memfd = fget(list[i].memfd);
>> >> +          if (!memfd)
>> >> +                  goto err_put_pages;
>> >> +          if (!shmem_mapping(file_inode(memfd)->i_mapping))
>> >> +                  goto err_put_pages;
>> >> +          seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
>> >> +          if (seals == -EINVAL ||
>> >> +              (seals & SEALS_WANTED) != SEALS_WANTED ||
>> >> +              (seals & SEALS_DENIED) != 0)
>> >> +                  goto err_put_pages;
>> >
>> > All these conditions will return -EINVAL. I'm not familiar with the memfd
>> > API, should some error conditions return a different error code to make
>> > them distinguishable by userspace ?
>>
>> Hmm, I guess EBADFD would be reasonable in case the file handle isn't a
>> memfd.  Other suggestions?
>
> I'll let others comment on this as I don't feel qualified to pick proper error
> codes, not being familiar with the memfd API.
>
>> I'll prepare a fixup patch series addressing most of the other
>> review comments.
>
> --
> Regards,
>
> Laurent Pinchart
>
>
>
Gerd Hoffmann Sept. 11, 2018, 12:03 p.m. UTC | #6
> > >> +	if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
> > >> +		return VM_FAULT_SIGBUS;
> > > 
> > > Just curious, when do you expect this to happen ?
> > 
> > It should not.  If it actually happens it would be a bug somewhere,
> > thats why the WARN_ON.
> 
> But you seem to consider that this condition that should never happen still 
> has a high enough chance of happening that it's worth a WARN_ON(). I was 
> wondering why this one in particular, and not other conditions that also can't 
> happen and are not checked through the code. 

Added it while writing the code, to get any coding mistake I make
flagged right away instead of things exploding later on.

I can drop it.

> > >> +	ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
> > > 
> > > sizeof(*ubuf)
> > 
> > Why?  Should not make a difference ...
> 
> Because the day we replace
> 
> 	struct udmabuf *ubuf;
> 
> with
> 
> 	struct udmabuf_ext *ubuf;
> 
> and forget to change the next line, we'll introduce a bug. That's why 
> sizeof(variable) is preferred over sizeof(type). Another reason is that I can 
> easily see that
> 
> 	ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL);
> 
> is correct, while using sizeof(type) requires me to go and look up the 
> declaration of the variable.

So it simplifies review, ok, will change it.

BTW: Maybe the kernel should pick up a neat trick from glib:

g_new0() is a macro which takes the type instead of the size as first
argument, and it casts the return value to that type.  So the compiler
will throw warnings in case of a mismatch.  That'll work better than
depending purely on the coder being careful and review catching the
remaining issues.

cheers,
  Gerd
Yann Droneaud Sept. 11, 2018, 8:47 p.m. UTC | #7
Hi,

Le lundi 27 août 2018 à 11:34 +0200, Gerd Hoffmann a écrit :
> A driver to let userspace turn memfd regions into dma-bufs.
> 
> Use case:  Allows qemu create dmabufs for the vga framebuffer or
> virtio-gpu ressources.  Then they can be passed around to display
> those guest things on the host.  To spice client for classic full
> framebuffer display, and hopefully some day to wayland server for
> seamless guest window display.
> 
> qemu test branch:
>   https://git.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf
> 
> Cc: David Airlie <airlied@linux.ie>
> Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  Documentation/ioctl/ioctl-number.txt              |   1 +
>  include/uapi/linux/udmabuf.h                      |  33 +++
>  drivers/dma-buf/udmabuf.c                         | 287
> ++++++++++++++++++++++
>  tools/testing/selftests/drivers/dma-buf/udmabuf.c |  96 ++++++++
>  MAINTAINERS                                       |  16 ++
>  drivers/dma-buf/Kconfig                           |   8 +
>  drivers/dma-buf/Makefile                          |   1 +
>  tools/testing/selftests/drivers/dma-buf/Makefile  |   5 +
>  8 files changed, 447 insertions(+)
>  create mode 100644 include/uapi/linux/udmabuf.h
>  create mode 100644 drivers/dma-buf/udmabuf.c
>  create mode 100644 tools/testing/selftests/drivers/dma-buf/udmabuf.c
>  create mode 100644 tools/testing/selftests/drivers/dma-buf/Makefile
> 
> diff --git a/include/uapi/linux/udmabuf.h
> b/include/uapi/linux/udmabuf.h
> new file mode 100644
> index 0000000000..46b6532ed8
> --- /dev/null
> +++ b/include/uapi/linux/udmabuf.h
> @@ -0,0 +1,33 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _UAPI_LINUX_UDMABUF_H
> +#define _UAPI_LINUX_UDMABUF_H
> +
> +#include <linux/types.h>
> +#include <linux/ioctl.h>
> +
> +#define UDMABUF_FLAGS_CLOEXEC	0x01
> +
> +struct udmabuf_create {
> +	__u32 memfd;
> +	__u32 flags;
> +	__u64 offset;
> +	__u64 size;
> +};
> +
> +struct udmabuf_create_item {
> +	__u32 memfd;
> +	__u32 __pad;
> +	__u64 offset;
> +	__u64 size;
> +};
> +
> +struct udmabuf_create_list {
> +	__u32 flags;
> +	__u32 count;
> +	struct udmabuf_create_item list[];
> +};
> +
> +#define UDMABUF_CREATE       _IOW('u', 0x42, struct udmabuf_create)
> +#define UDMABUF_CREATE_LIST  _IOW('u', 0x43, struct
> udmabuf_create_list)
> +
> +#endif /* _UAPI_LINUX_UDMABUF_H */
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> new file mode 100644
> index 0000000000..8e24204526
> --- /dev/null
> +++ b/drivers/dma-buf/udmabuf.c
> +static long udmabuf_create(struct udmabuf_create_list *head,
> +			   struct udmabuf_create_item *list)
> +{
> +	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> +	struct file *memfd = NULL;
> +	struct udmabuf *ubuf;
> +	struct dma_buf *buf;
> +	pgoff_t pgoff, pgcnt, pgidx, pgbuf;
> +	struct page *page;
> +	int seals, ret = -EINVAL;
> +	u32 i, flags;
> +
> +	ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
> +	if (!ubuf)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < head->count; i++) {

You need to check .__pad for unsupported value:

                if (list[i].__pad) {
                        ret = -EINVAL;
                        goto err_free_ubuf;
                }

> +		if (!IS_ALIGNED(list[i].offset, PAGE_SIZE))
> +			goto err_free_ubuf;
> +		if (!IS_ALIGNED(list[i].size, PAGE_SIZE))
> +			goto err_free_ubuf;
> +		ubuf->pagecount += list[i].size >> PAGE_SHIFT;
> +	}
> +	ubuf->pages = kmalloc_array(ubuf->pagecount, sizeof(struct page
> *),
> +				    GFP_KERNEL);
> +	if (!ubuf->pages) {
> +		ret = -ENOMEM;
> +		goto err_free_ubuf;
> +	}
> +
> +	pgbuf = 0;
> +	for (i = 0; i < head->count; i++) {
> +		memfd = fget(list[i].memfd);
> +		if (!memfd)
> +			goto err_put_pages;
> +		if (!shmem_mapping(file_inode(memfd)->i_mapping))
> +			goto err_put_pages;
> +		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
> +		if (seals == -EINVAL ||
> +		    (seals & SEALS_WANTED) != SEALS_WANTED ||
> +		    (seals & SEALS_DENIED) != 0)
> +			goto err_put_pages;
> +		pgoff = list[i].offset >> PAGE_SHIFT;
> +		pgcnt = list[i].size   >> PAGE_SHIFT;
> +		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
> +			page = shmem_read_mapping_page(
> +				file_inode(memfd)->i_mapping, pgoff +
> pgidx);
> +			if (IS_ERR(page)) {
> +				ret = PTR_ERR(page);
> +				goto err_put_pages;
> +			}
> +			ubuf->pages[pgbuf++] = page;
> +		}
> +		fput(memfd);
> +	}
> +	memfd = NULL;
> +
> +	exp_info.ops  = &udmabuf_ops;
> +	exp_info.size = ubuf->pagecount << PAGE_SHIFT;
> +	exp_info.priv = ubuf;
> +
> +	buf = dma_buf_export(&exp_info);
> +	if (IS_ERR(buf)) {
> +		ret = PTR_ERR(buf);
> +		goto err_put_pages;
> +	}
> +
> +	flags = 0;

You need to check .flags for unsupported value:

        if (head->flags & ~UDMABUF_FLAGS_CLOEXEC)
                 return -EINVAL;

(at the beginning of the function, of course).

> +	if (head->flags & UDMABUF_FLAGS_CLOEXEC)
> +		flags |= O_CLOEXEC;
> +	return dma_buf_fd(buf, flags);
> +
> +err_put_pages:
> +	while (pgbuf > 0)
> +		put_page(ubuf->pages[--pgbuf]);
> +err_free_ubuf:
> +	fput(memfd);
> +	kfree(ubuf->pages);
> +	kfree(ubuf);
> +	return ret;
> +}
> +

Regards

Patch
diff mbox series

diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index 13a7c999c0..f2ac672eb7 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -272,6 +272,7 @@  Code  Seq#(hex)	Include File		Comments
 't'	90-91	linux/toshiba.h		toshiba and toshiba_acpi SMM
 'u'	00-1F	linux/smb_fs.h		gone
 'u'	20-3F	linux/uvcvideo.h	USB video class host driver
+'u'	40-4f	linux/udmabuf.h		userspace dma-buf misc device
 'v'	00-1F	linux/ext2_fs.h		conflict!
 'v'	00-1F	linux/fs.h		conflict!
 'v'	00-0F	linux/sonypi.h		conflict!
diff --git a/include/uapi/linux/udmabuf.h b/include/uapi/linux/udmabuf.h
new file mode 100644
index 0000000000..46b6532ed8
--- /dev/null
+++ b/include/uapi/linux/udmabuf.h
@@ -0,0 +1,33 @@ 
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_UDMABUF_H
+#define _UAPI_LINUX_UDMABUF_H
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+#define UDMABUF_FLAGS_CLOEXEC	0x01
+
+struct udmabuf_create {
+	__u32 memfd;
+	__u32 flags;
+	__u64 offset;
+	__u64 size;
+};
+
+struct udmabuf_create_item {
+	__u32 memfd;
+	__u32 __pad;
+	__u64 offset;
+	__u64 size;
+};
+
+struct udmabuf_create_list {
+	__u32 flags;
+	__u32 count;
+	struct udmabuf_create_item list[];
+};
+
+#define UDMABUF_CREATE       _IOW('u', 0x42, struct udmabuf_create)
+#define UDMABUF_CREATE_LIST  _IOW('u', 0x43, struct udmabuf_create_list)
+
+#endif /* _UAPI_LINUX_UDMABUF_H */
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
new file mode 100644
index 0000000000..8e24204526
--- /dev/null
+++ b/drivers/dma-buf/udmabuf.c
@@ -0,0 +1,287 @@ 
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/miscdevice.h>
+#include <linux/dma-buf.h>
+#include <linux/highmem.h>
+#include <linux/cred.h>
+#include <linux/shmem_fs.h>
+#include <linux/memfd.h>
+
+#include <uapi/linux/udmabuf.h>
+
+struct udmabuf {
+	u32 pagecount;
+	struct page **pages;
+};
+
+static int udmabuf_vm_fault(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct udmabuf *ubuf = vma->vm_private_data;
+
+	if (WARN_ON(vmf->pgoff >= ubuf->pagecount))
+		return VM_FAULT_SIGBUS;
+
+	vmf->page = ubuf->pages[vmf->pgoff];
+	get_page(vmf->page);
+	return 0;
+}
+
+static const struct vm_operations_struct udmabuf_vm_ops = {
+	.fault = udmabuf_vm_fault,
+};
+
+static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
+{
+	struct udmabuf *ubuf = buf->priv;
+
+	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
+		return -EINVAL;
+
+	vma->vm_ops = &udmabuf_vm_ops;
+	vma->vm_private_data = ubuf;
+	return 0;
+}
+
+static struct sg_table *map_udmabuf(struct dma_buf_attachment *at,
+				    enum dma_data_direction direction)
+{
+	struct udmabuf *ubuf = at->dmabuf->priv;
+	struct sg_table *sg;
+
+	sg = kzalloc(sizeof(*sg), GFP_KERNEL);
+	if (!sg)
+		goto err1;
+	if (sg_alloc_table_from_pages(sg, ubuf->pages, ubuf->pagecount,
+				      0, ubuf->pagecount << PAGE_SHIFT,
+				      GFP_KERNEL) < 0)
+		goto err2;
+	if (!dma_map_sg(at->dev, sg->sgl, sg->nents, direction))
+		goto err3;
+
+	return sg;
+
+err3:
+	sg_free_table(sg);
+err2:
+	kfree(sg);
+err1:
+	return ERR_PTR(-ENOMEM);
+}
+
+static void unmap_udmabuf(struct dma_buf_attachment *at,
+			  struct sg_table *sg,
+			  enum dma_data_direction direction)
+{
+	sg_free_table(sg);
+	kfree(sg);
+}
+
+static void release_udmabuf(struct dma_buf *buf)
+{
+	struct udmabuf *ubuf = buf->priv;
+	pgoff_t pg;
+
+	for (pg = 0; pg < ubuf->pagecount; pg++)
+		put_page(ubuf->pages[pg]);
+	kfree(ubuf->pages);
+	kfree(ubuf);
+}
+
+static void *kmap_udmabuf(struct dma_buf *buf, unsigned long page_num)
+{
+	struct udmabuf *ubuf = buf->priv;
+	struct page *page = ubuf->pages[page_num];
+
+	return kmap(page);
+}
+
+static void kunmap_udmabuf(struct dma_buf *buf, unsigned long page_num,
+			   void *vaddr)
+{
+	kunmap(vaddr);
+}
+
+static struct dma_buf_ops udmabuf_ops = {
+	.map_dma_buf	  = map_udmabuf,
+	.unmap_dma_buf	  = unmap_udmabuf,
+	.release	  = release_udmabuf,
+	.map		  = kmap_udmabuf,
+	.unmap		  = kunmap_udmabuf,
+	.mmap		  = mmap_udmabuf,
+};
+
+#define SEALS_WANTED (F_SEAL_SHRINK)
+#define SEALS_DENIED (F_SEAL_WRITE)
+
+static long udmabuf_create(struct udmabuf_create_list *head,
+			   struct udmabuf_create_item *list)
+{
+	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+	struct file *memfd = NULL;
+	struct udmabuf *ubuf;
+	struct dma_buf *buf;
+	pgoff_t pgoff, pgcnt, pgidx, pgbuf;
+	struct page *page;
+	int seals, ret = -EINVAL;
+	u32 i, flags;
+
+	ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
+	if (!ubuf)
+		return -ENOMEM;
+
+	for (i = 0; i < head->count; i++) {
+		if (!IS_ALIGNED(list[i].offset, PAGE_SIZE))
+			goto err_free_ubuf;
+		if (!IS_ALIGNED(list[i].size, PAGE_SIZE))
+			goto err_free_ubuf;
+		ubuf->pagecount += list[i].size >> PAGE_SHIFT;
+	}
+	ubuf->pages = kmalloc_array(ubuf->pagecount, sizeof(struct page *),
+				    GFP_KERNEL);
+	if (!ubuf->pages) {
+		ret = -ENOMEM;
+		goto err_free_ubuf;
+	}
+
+	pgbuf = 0;
+	for (i = 0; i < head->count; i++) {
+		memfd = fget(list[i].memfd);
+		if (!memfd)
+			goto err_put_pages;
+		if (!shmem_mapping(file_inode(memfd)->i_mapping))
+			goto err_put_pages;
+		seals = memfd_fcntl(memfd, F_GET_SEALS, 0);
+		if (seals == -EINVAL ||
+		    (seals & SEALS_WANTED) != SEALS_WANTED ||
+		    (seals & SEALS_DENIED) != 0)
+			goto err_put_pages;
+		pgoff = list[i].offset >> PAGE_SHIFT;
+		pgcnt = list[i].size   >> PAGE_SHIFT;
+		for (pgidx = 0; pgidx < pgcnt; pgidx++) {
+			page = shmem_read_mapping_page(
+				file_inode(memfd)->i_mapping, pgoff + pgidx);
+			if (IS_ERR(page)) {
+				ret = PTR_ERR(page);
+				goto err_put_pages;
+			}
+			ubuf->pages[pgbuf++] = page;
+		}
+		fput(memfd);
+	}
+	memfd = NULL;
+
+	exp_info.ops  = &udmabuf_ops;
+	exp_info.size = ubuf->pagecount << PAGE_SHIFT;
+	exp_info.priv = ubuf;
+
+	buf = dma_buf_export(&exp_info);
+	if (IS_ERR(buf)) {
+		ret = PTR_ERR(buf);
+		goto err_put_pages;
+	}
+
+	flags = 0;
+	if (head->flags & UDMABUF_FLAGS_CLOEXEC)
+		flags |= O_CLOEXEC;
+	return dma_buf_fd(buf, flags);
+
+err_put_pages:
+	while (pgbuf > 0)
+		put_page(ubuf->pages[--pgbuf]);
+err_free_ubuf:
+	fput(memfd);
+	kfree(ubuf->pages);
+	kfree(ubuf);
+	return ret;
+}
+
+static long udmabuf_ioctl_create(struct file *filp, unsigned long arg)
+{
+	struct udmabuf_create create;
+	struct udmabuf_create_list head;
+	struct udmabuf_create_item list;
+
+	if (copy_from_user(&create, (void __user *)arg,
+			   sizeof(struct udmabuf_create)))
+		return -EFAULT;
+
+	head.flags  = create.flags;
+	head.count  = 1;
+	list.memfd  = create.memfd;
+	list.offset = create.offset;
+	list.size   = create.size;
+
+	return udmabuf_create(&head, &list);
+}
+
+static long udmabuf_ioctl_create_list(struct file *filp, unsigned long arg)
+{
+	struct udmabuf_create_list head;
+	struct udmabuf_create_item *list;
+	int ret = -EINVAL;
+	u32 lsize;
+
+	if (copy_from_user(&head, (void __user *)arg, sizeof(head)))
+		return -EFAULT;
+	if (head.count > 1024)
+		return -EINVAL;
+	lsize = sizeof(struct udmabuf_create_item) * head.count;
+	list = memdup_user((void __user *)(arg + sizeof(head)), lsize);
+	if (IS_ERR(list))
+		return PTR_ERR(list);
+
+	ret = udmabuf_create(&head, list);
+	kfree(list);
+	return ret;
+}
+
+static long udmabuf_ioctl(struct file *filp, unsigned int ioctl,
+			  unsigned long arg)
+{
+	long ret;
+
+	switch (ioctl) {
+	case UDMABUF_CREATE:
+		ret = udmabuf_ioctl_create(filp, arg);
+		break;
+	case UDMABUF_CREATE_LIST:
+		ret = udmabuf_ioctl_create_list(filp, arg);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+	return ret;
+}
+
+static const struct file_operations udmabuf_fops = {
+	.owner		= THIS_MODULE,
+	.unlocked_ioctl = udmabuf_ioctl,
+};
+
+static struct miscdevice udmabuf_misc = {
+	.minor          = MISC_DYNAMIC_MINOR,
+	.name           = "udmabuf",
+	.fops           = &udmabuf_fops,
+};
+
+static int __init udmabuf_dev_init(void)
+{
+	return misc_register(&udmabuf_misc);
+}
+
+static void __exit udmabuf_dev_exit(void)
+{
+	misc_deregister(&udmabuf_misc);
+}
+
+module_init(udmabuf_dev_init)
+module_exit(udmabuf_dev_exit)
+
+MODULE_AUTHOR("Gerd Hoffmann <kraxel@redhat.com>");
+MODULE_LICENSE("GPL v2");
diff --git a/tools/testing/selftests/drivers/dma-buf/udmabuf.c b/tools/testing/selftests/drivers/dma-buf/udmabuf.c
new file mode 100644
index 0000000000..376b1d6730
--- /dev/null
+++ b/tools/testing/selftests/drivers/dma-buf/udmabuf.c
@@ -0,0 +1,96 @@ 
+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <malloc.h>
+
+#include <sys/ioctl.h>
+#include <sys/syscall.h>
+#include <linux/memfd.h>
+#include <linux/udmabuf.h>
+
+#define TEST_PREFIX	"drivers/dma-buf/udmabuf"
+#define NUM_PAGES       4
+
+static int memfd_create(const char *name, unsigned int flags)
+{
+	return syscall(__NR_memfd_create, name, flags);
+}
+
+int main(int argc, char *argv[])
+{
+	struct udmabuf_create create;
+	int devfd, memfd, buf, ret;
+	off_t size;
+	void *mem;
+
+	devfd = open("/dev/udmabuf", O_RDWR);
+	if (devfd < 0) {
+		printf("%s: [skip,no-udmabuf]\n", TEST_PREFIX);
+		exit(77);
+	}
+
+	memfd = memfd_create("udmabuf-test", MFD_CLOEXEC);
+	if (memfd < 0) {
+		printf("%s: [skip,no-memfd]\n", TEST_PREFIX);
+		exit(77);
+	}
+
+	size = getpagesize() * NUM_PAGES;
+	ret = ftruncate(memfd, size);
+	if (ret == -1) {
+		printf("%s: [FAIL,memfd-truncate]\n", TEST_PREFIX);
+		exit(1);
+	}
+
+	memset(&create, 0, sizeof(create));
+
+	/* should fail (offset not page aligned) */
+	create.memfd  = memfd;
+	create.offset = getpagesize()/2;
+	create.size   = getpagesize();
+	buf = ioctl(devfd, UDMABUF_CREATE, &create);
+	if (buf >= 0) {
+		printf("%s: [FAIL,test-1]\n", TEST_PREFIX);
+		exit(1);
+	}
+
+	/* should fail (size not multiple of page) */
+	create.memfd  = memfd;
+	create.offset = 0;
+	create.size   = getpagesize()/2;
+	buf = ioctl(devfd, UDMABUF_CREATE, &create);
+	if (buf >= 0) {
+		printf("%s: [FAIL,test-2]\n", TEST_PREFIX);
+		exit(1);
+	}
+
+	/* should fail (not memfd) */
+	create.memfd  = 0; /* stdin */
+	create.offset = 0;
+	create.size   = size;
+	buf = ioctl(devfd, UDMABUF_CREATE, &create);
+	if (buf >= 0) {
+		printf("%s: [FAIL,test-3]\n", TEST_PREFIX);
+		exit(1);
+	}
+
+	/* should work */
+	create.memfd  = memfd;
+	create.offset = 0;
+	create.size   = size;
+	buf = ioctl(devfd, UDMABUF_CREATE, &create);
+	if (buf < 0) {
+		printf("%s: [FAIL,test-4]\n", TEST_PREFIX);
+		exit(1);
+	}
+
+	fprintf(stderr, "%s: ok\n", TEST_PREFIX);
+	close(buf);
+	close(memfd);
+	close(devfd);
+	return 0;
+}
diff --git a/MAINTAINERS b/MAINTAINERS
index a5b256b259..11a9b04277 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14934,6 +14934,14 @@  S:	Maintained
 F:	Documentation/filesystems/udf.txt
 F:	fs/udf/
 
+UDMABUF DRIVER
+M:	Gerd Hoffmann <kraxel@redhat.com>
+L:	dri-devel@lists.freedesktop.org
+S:	Maintained
+F:	drivers/dma-buf/udmabuf.c
+F:	include/uapi/linux/udmabuf.h
+F:	tools/testing/selftests/drivers/dma-buf/udmabuf.c
+
 UDRAW TABLET
 M:	Bastien Nocera <hadess@hadess.net>
 L:	linux-input@vger.kernel.org
@@ -15343,6 +15351,14 @@  F:	arch/x86/um/
 F:	fs/hostfs/
 F:	fs/hppfs/
 
+USERSPACE DMA BUFFER DRIVER
+M:	Gerd Hoffmann <kraxel@redhat.com>
+S:	Maintained
+L:	dri-devel@lists.freedesktop.org
+F:	drivers/dma-buf/udmabuf.c
+F:	include/uapi/linux/udmabuf.h
+T:	git git://anongit.freedesktop.org/drm/drm-misc
+
 USERSPACE I/O (UIO)
 M:	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 S:	Maintained
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
index ed3b785bae..338129eb12 100644
--- a/drivers/dma-buf/Kconfig
+++ b/drivers/dma-buf/Kconfig
@@ -30,4 +30,12 @@  config SW_SYNC
 	  WARNING: improper use of this can result in deadlocking kernel
 	  drivers from userspace. Intended for test and debug only.
 
+config UDMABUF
+	bool "userspace dmabuf misc driver"
+	default n
+	depends on DMA_SHARED_BUFFER
+	help
+	  A driver to let userspace turn memfd regions into dma-bufs.
+	  Qemu can use this to create host dmabufs for guest framebuffers.
+
 endmenu
diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
index c33bf88631..0913a6ccab 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -1,3 +1,4 @@ 
 obj-y := dma-buf.o dma-fence.o dma-fence-array.o reservation.o seqno-fence.o
 obj-$(CONFIG_SYNC_FILE)		+= sync_file.o
 obj-$(CONFIG_SW_SYNC)		+= sw_sync.o sync_debug.o
+obj-$(CONFIG_UDMABUF)		+= udmabuf.o
diff --git a/tools/testing/selftests/drivers/dma-buf/Makefile b/tools/testing/selftests/drivers/dma-buf/Makefile
new file mode 100644
index 0000000000..4154c3d7aa
--- /dev/null
+++ b/tools/testing/selftests/drivers/dma-buf/Makefile
@@ -0,0 +1,5 @@ 
+CFLAGS += -I../../../../../usr/include/
+
+TEST_GEN_PROGS := udmabuf
+
+include ../../lib.mk