Re: [PATCH v3] Add udmabuf misc device

[Daniel Vetter]

On Fri, May 25, 2018 at 04:08:08PM +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.
> 
> Note: Initial revision which supports a single region only so it
>       can't handle virtio-gpu ressources yet.
> 
> qemu test branch:
>   https://git.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf
> 
> Cc: David Airlie <airlied@xxxxxxxx>
> Cc: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> ---
>  include/uapi/linux/udmabuf.h                      |  19 ++
>  drivers/dma-buf/udmabuf.c                         | 240 ++++++++++++++++++++++
>  tools/testing/selftests/drivers/dma-buf/udmabuf.c |  95 +++++++++
>  drivers/dma-buf/Kconfig                           |   7 +
>  drivers/dma-buf/Makefile                          |   1 +
>  tools/testing/selftests/drivers/dma-buf/Makefile  |   5 +
>  6 files changed, 367 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..2fbe69cf05
> --- /dev/null
> +++ b/include/uapi/linux/udmabuf.h
> @@ -0,0 +1,19 @@
> +/* 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;
> +};
> +
> +#define UDMABUF_CREATE _IOW(0x42, 0x23, struct udmabuf_create)
> +
> +#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..f9600dc985
> --- /dev/null
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -0,0 +1,240 @@
> +/*
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +#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 <uapi/linux/udmabuf.h>
> +
> +struct udmabuf {
> +	struct file *filp;
> +	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) == 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]);
> +	fput(ubuf->filp);
> +	kfree(ubuf->pages);
> +	kfree(ubuf);
> +}
> +
> +static void *kmap_atomic_udmabuf(struct dma_buf *buf, unsigned long page_num)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +	struct page *page = ubuf->pages[page_num];
> +
> +	return kmap_atomic(page);
> +}
> +
> +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);
> +}

The above leaks like mad since no kunamp?

Also I think we have 0 users of the kmap atomic interfaces ... so not sure
whether it's worth it to implement those.
-Daniel

> +
> +static struct dma_buf_ops udmabuf_ops = {
> +	.map_dma_buf	  = map_udmabuf,
> +	.unmap_dma_buf	  = unmap_udmabuf,
> +	.release	  = release_udmabuf,
> +	.map_atomic	  = kmap_atomic_udmabuf,
> +	.map		  = kmap_udmabuf,
> +	.mmap		  = mmap_udmabuf,
> +};
> +
> +static long udmabuf_ioctl_create(struct file *filp, unsigned long arg)
> +{
> +	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> +	struct udmabuf_create create;
> +	struct udmabuf *ubuf;
> +	struct dma_buf *buf;
> +	pgoff_t pgoff, pgidx;
> +	struct page *page;
> +	int ret = -EINVAL;
> +	u32 flags;
> +
> +	if (copy_from_user(&create, (void __user *)arg,
> +			   sizeof(struct udmabuf_create)))
> +		return -EFAULT;
> +
> +	if (!IS_ALIGNED(create.offset, PAGE_SIZE))
> +		return -EINVAL;
> +	if (!IS_ALIGNED(create.size, PAGE_SIZE))
> +		return -EINVAL;
> +
> +	ubuf = kzalloc(sizeof(struct udmabuf), GFP_KERNEL);
> +	if (!ubuf)
> +		return -ENOMEM;
> +
> +	ubuf->filp = fget(create.memfd);
> +	if (!ubuf->filp)
> +		goto err_free_ubuf;
> +	if (!shmem_mapping(file_inode(ubuf->filp)->i_mapping))
> +		goto err_free_ubuf;
> +
> +	ubuf->pagecount = create.size >> PAGE_SHIFT;
> +	ubuf->pages = kmalloc_array(ubuf->pagecount, sizeof(struct page*),
> +				    GFP_KERNEL);
> +	if (!ubuf->pages) {
> +		ret = -ENOMEM;
> +		goto err_free_ubuf;
> +	}
> +
> +	pgoff = create.offset >> PAGE_SHIFT;
> +	for (pgidx = 0; pgidx < ubuf->pagecount; pgidx++) {
> +		page = shmem_read_mapping_page(
> +			file_inode(ubuf->filp)->i_mapping, pgoff + pgidx);
> +		if (IS_ERR(page)) {
> +			ret = PTR_ERR(buf);
> +			goto err_put_pages;
> +		}
> +		ubuf->pages[pgidx] = page;
> +	}
> +
> +	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 (create.flags & UDMABUF_FLAGS_CLOEXEC)
> +		flags |= O_CLOEXEC;
> +	return dma_buf_fd(buf, flags);
> +
> +err_put_pages:
> +	while (pgidx > 0)
> +		put_page(ubuf->pages[--pgidx]);
> +err_free_ubuf:
> +	fput(ubuf->filp);
> +	kfree(ubuf->pages);
> +	kfree(ubuf);
> +	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;
> +	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@xxxxxxxxxx>");
> +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..d46c58b0dd
> --- /dev/null
> +++ b/tools/testing/selftests/drivers/dma-buf/udmabuf.c
> @@ -0,0 +1,95 @@
> +#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/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
> index ed3b785bae..19be3ec62d 100644
> --- a/drivers/dma-buf/Kconfig
> +++ b/drivers/dma-buf/Kconfig
> @@ -30,4 +30,11 @@ 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 iovs into dma-bufs.
> +
>  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
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch