[RFC PATCH 01/10] dma-buf: add support for paged attachment mappings
Christian König
christian.koenig at amd.com
Tue Jul 11 07:59:00 UTC 2023
Am 11.07.23 um 00:32 schrieb Mina Almasry:
> Currently dmabuf p2p memory doesn't present itself in the form of struct
> pages and the memory can't be easily used with code that expects memory
> in that form.
Well, this won't fly at all.
First of all DMA-buf is *not* about passing struct pages around, drivers
are *only* supposed to use the DMA addresses.
That code can't use the pages inside a DMA-buf is absolutely
intentional. We even mangle the page pointers from the sg_tables because
people sometimes get the impression they can use those.
See function mangle_sg_table() in dma-buf.c
/* To catch abuse of the underlying struct page by importers mix
* up the bits, but take care to preserve the low SG_ bits to
* not corrupt the sgt. The mixing is undone in __unmap_dma_buf
* before passing the sgt back to the exporter. */
for_each_sgtable_sg(sg_table, sg, i)
sg->page_link ^= ~0xffUL;
> Add support for paged attachment mappings. We use existing
> dmabuf APIs to create a mapped attachment (dma_buf_attach() &
> dma_buf_map_attachment()), and we create struct pages for this mapping.
> We write the dma_addr's from the sg_table into the created pages.
Hui, what? Not really.
Regards,
Christian.
> These
> pages can then be passed into code that expects struct pages and can
> largely operate on these pages with minimal modifications:
>
> 1. The pages need not be dma mapped. The dma addr can be queried from
> page->zone_device_data and used directly.
> 2. The pages are not kmappable.
>
> Add a new ioctl that enables the user to create a struct page backed
> dmabuf attachment mapping. This ioctl returns a new file descriptor
> which represents the dmabuf pages. The pages are freed when (a) the
> user closes the file, and (b) the struct pages backing the dmabuf are
> no longer in use. Once the pages are no longer in use, the mapped
> attachment is removed.
>
> The support added in this patch should be generic - the pages are created
> by the base code, but the user specifies the type of page to create using
> the dmabuf_create_pages_info->type flag. The base code hands of any
> handling specific to the use case of the ops of that page type.
>
> Signed-off-by: Mina Almasry <almasrymina at google.com>
> ---
> drivers/dma-buf/dma-buf.c | 223 +++++++++++++++++++++++++++++++++++
> include/linux/dma-buf.h | 90 ++++++++++++++
> include/uapi/linux/dma-buf.h | 9 ++
> 3 files changed, 322 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index aa4ea8530cb3..50b1d813cf5c 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -22,6 +22,7 @@
> #include <linux/module.h>
> #include <linux/seq_file.h>
> #include <linux/sync_file.h>
> +#include <linux/pci.h>
> #include <linux/poll.h>
> #include <linux/dma-resv.h>
> #include <linux/mm.h>
> @@ -442,12 +443,16 @@ static long dma_buf_import_sync_file(struct dma_buf *dmabuf,
> }
> #endif
>
> +static long dma_buf_create_pages(struct file *file,
> + struct dma_buf_create_pages_info *create_info);
> +
> static long dma_buf_ioctl(struct file *file,
> unsigned int cmd, unsigned long arg)
> {
> struct dma_buf *dmabuf;
> struct dma_buf_sync sync;
> enum dma_data_direction direction;
> + struct dma_buf_create_pages_info create_info;
> int ret;
>
> dmabuf = file->private_data;
> @@ -484,6 +489,12 @@ static long dma_buf_ioctl(struct file *file,
> case DMA_BUF_SET_NAME_A:
> case DMA_BUF_SET_NAME_B:
> return dma_buf_set_name(dmabuf, (const char __user *)arg);
> + case DMA_BUF_CREATE_PAGES:
> + if (copy_from_user(&create_info, (void __user *)arg,
> + sizeof(create_info)))
> + return -EFAULT;
> +
> + return dma_buf_create_pages(file, &create_info);
>
> #if IS_ENABLED(CONFIG_SYNC_FILE)
> case DMA_BUF_IOCTL_EXPORT_SYNC_FILE:
> @@ -1613,6 +1624,218 @@ void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map)
> }
> EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap_unlocked, DMA_BUF);
>
> +static int dma_buf_pages_release(struct inode *inode, struct file *file)
> +{
> + struct dma_buf_pages *priv = file->private_data;
> +
> + if (priv->type_ops->dma_buf_pages_release)
> + priv->type_ops->dma_buf_pages_release(priv, file);
> +
> + percpu_ref_kill(&priv->pgmap.ref);
> + /* Drop initial ref after percpu_ref_kill(). */
> + percpu_ref_put(&priv->pgmap.ref);
> +
> + return 0;
> +}
> +
> +static void dma_buf_page_free(struct page *page)
> +{
> + struct dma_buf_pages *priv;
> + struct dev_pagemap *pgmap;
> +
> + pgmap = page->pgmap;
> + priv = container_of(pgmap, struct dma_buf_pages, pgmap);
> +
> + if (priv->type_ops->dma_buf_page_free)
> + priv->type_ops->dma_buf_page_free(priv, page);
> +}
> +
> +const struct dev_pagemap_ops dma_buf_pgmap_ops = {
> + .page_free = dma_buf_page_free,
> +};
> +EXPORT_SYMBOL_GPL(dma_buf_pgmap_ops);
> +
> +const struct file_operations dma_buf_pages_fops = {
> + .release = dma_buf_pages_release,
> +};
> +EXPORT_SYMBOL_GPL(dma_buf_pages_fops);
> +
> +#ifdef CONFIG_ZONE_DEVICE
> +static void dma_buf_pages_destroy(struct percpu_ref *ref)
> +{
> + struct dma_buf_pages *priv;
> + struct dev_pagemap *pgmap;
> +
> + pgmap = container_of(ref, struct dev_pagemap, ref);
> + priv = container_of(pgmap, struct dma_buf_pages, pgmap);
> +
> + if (priv->type_ops->dma_buf_pages_destroy)
> + priv->type_ops->dma_buf_pages_destroy(priv);
> +
> + kvfree(priv->pages);
> + kfree(priv);
> +
> + dma_buf_unmap_attachment(priv->attachment, priv->sgt, priv->direction);
> + dma_buf_detach(priv->dmabuf, priv->attachment);
> + dma_buf_put(priv->dmabuf);
> + pci_dev_put(priv->pci_dev);
> +}
> +
> +static long dma_buf_create_pages(struct file *file,
> + struct dma_buf_create_pages_info *create_info)
> +{
> + int err, fd, i, pg_idx;
> + struct scatterlist *sg;
> + struct dma_buf_pages *priv;
> + struct file *new_file;
> +
> + fd = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
> + if (fd < 0) {
> + err = fd;
> + goto out_err;
> + }
> +
> + priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> + if (!priv) {
> + err = -ENOMEM;
> + goto out_put_fd;
> + }
> +
> + priv->pgmap.type = MEMORY_DEVICE_PRIVATE;
> + priv->pgmap.ops = &dma_buf_pgmap_ops;
> + init_completion(&priv->pgmap.done);
> +
> + /* This refcount is incremented every time a page in priv->pages is
> + * allocated, and decremented every time a page is freed. When
> + * it drops to 0, the dma_buf_pages can be destroyed. An initial ref is
> + * held and the dma_buf_pages is not destroyed until that is dropped.
> + */
> + err = percpu_ref_init(&priv->pgmap.ref, dma_buf_pages_destroy, 0,
> + GFP_KERNEL);
> + if (err)
> + goto out_free_priv;
> +
> + /* Initial ref to be dropped after percpu_ref_kill(). */
> + percpu_ref_get(&priv->pgmap.ref);
> +
> + priv->pci_dev = pci_get_domain_bus_and_slot(
> + 0, create_info->pci_bdf[0],
> + PCI_DEVFN(create_info->pci_bdf[1], create_info->pci_bdf[2]));
> + if (!priv->pci_dev) {
> + err = -ENODEV;
> + goto out_exit_percpu_ref;
> + }
> +
> + priv->dmabuf = dma_buf_get(create_info->dma_buf_fd);
> + if (IS_ERR(priv->dmabuf)) {
> + err = PTR_ERR(priv->dmabuf);
> + goto out_put_pci_dev;
> + }
> +
> + if (priv->dmabuf->size % PAGE_SIZE != 0) {
> + err = -EINVAL;
> + goto out_put_dma_buf;
> + }
> +
> + priv->attachment = dma_buf_attach(priv->dmabuf, &priv->pci_dev->dev);
> + if (IS_ERR(priv->attachment)) {
> + err = PTR_ERR(priv->attachment);
> + goto out_put_dma_buf;
> + }
> +
> + priv->num_pages = priv->dmabuf->size / PAGE_SIZE;
> + priv->pages = kvmalloc_array(priv->num_pages, sizeof(struct page),
> + GFP_KERNEL);
> + if (!priv->pages) {
> + err = -ENOMEM;
> + goto out_detach_dma_buf;
> + }
> +
> + for (i = 0; i < priv->num_pages; i++) {
> + struct page *page = &priv->pages[i];
> +
> + mm_zero_struct_page(page);
> + set_page_zone(page, ZONE_DEVICE);
> + set_page_count(page, 1);
> + page->pgmap = &priv->pgmap;
> + }
> +
> + priv->direction = DMA_BIDIRECTIONAL;
> + priv->sgt = dma_buf_map_attachment(priv->attachment, priv->direction);
> + if (IS_ERR(priv->sgt)) {
> + err = PTR_ERR(priv->sgt);
> + goto out_free_pages;
> + }
> +
> + /* write each dma addresses from sgt to each page */
> + pg_idx = 0;
> + for_each_sgtable_dma_sg(priv->sgt, sg, i) {
> + size_t len = sg_dma_len(sg);
> + dma_addr_t dma_addr = sg_dma_address(sg);
> +
> + BUG_ON(!PAGE_ALIGNED(len));
> + while (len > 0) {
> + priv->pages[pg_idx].zone_device_data = (void *)dma_addr;
> + pg_idx++;
> + dma_addr += PAGE_SIZE;
> + len -= PAGE_SIZE;
> + }
> + }
> +
> + new_file = anon_inode_getfile("[dma_buf_pages]", &dma_buf_pages_fops,
> + (void *)priv, O_RDWR | O_CLOEXEC);
> + if (IS_ERR(new_file)) {
> + err = PTR_ERR(new_file);
> + goto out_unmap_dma_buf;
> + }
> +
> + priv->type = create_info->type;
> + priv->create_flags = create_info->create_flags;
> +
> + switch (priv->type) {
> + default:
> + err = -EINVAL;
> + goto out_put_new_file;
> + }
> +
> + if (priv->type_ops->dma_buf_pages_init) {
> + err = priv->type_ops->dma_buf_pages_init(priv, new_file);
> + if (err)
> + goto out_put_new_file;
> + }
> +
> + fd_install(fd, new_file);
> + return fd;
> +
> +out_put_new_file:
> + fput(new_file);
> +out_unmap_dma_buf:
> + dma_buf_unmap_attachment(priv->attachment, priv->sgt, priv->direction);
> +out_free_pages:
> + kvfree(priv->pages);
> +out_detach_dma_buf:
> + dma_buf_detach(priv->dmabuf, priv->attachment);
> +out_put_dma_buf:
> + dma_buf_put(priv->dmabuf);
> +out_put_pci_dev:
> + pci_dev_put(priv->pci_dev);
> +out_exit_percpu_ref:
> + percpu_ref_exit(&priv->pgmap.ref);
> +out_free_priv:
> + kfree(priv);
> +out_put_fd:
> + put_unused_fd(fd);
> +out_err:
> + return err;
> +}
> +#else
> +static long dma_buf_create_pages(struct file *file,
> + struct dma_buf_create_pages_info *create_info)
> +{
> + return -ENOTSUPP;
> +}
> +#endif
> +
> #ifdef CONFIG_DEBUG_FS
> static int dma_buf_debug_show(struct seq_file *s, void *unused)
> {
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 3f31baa3293f..5789006180ea 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -540,6 +540,36 @@ struct dma_buf_export_info {
> void *priv;
> };
>
> +struct dma_buf_pages;
> +
> +struct dma_buf_pages_type_ops {
> + int (*dma_buf_pages_init)(struct dma_buf_pages *priv,
> + struct file *file);
> + void (*dma_buf_pages_release)(struct dma_buf_pages *priv,
> + struct file *file);
> + void (*dma_buf_pages_destroy)(struct dma_buf_pages *priv);
> + void (*dma_buf_page_free)(struct dma_buf_pages *priv,
> + struct page *page);
> +};
> +
> +struct dma_buf_pages {
> + /* fields for dmabuf */
> + struct dma_buf *dmabuf;
> + struct dma_buf_attachment *attachment;
> + struct sg_table *sgt;
> + struct pci_dev *pci_dev;
> + enum dma_data_direction direction;
> +
> + /* fields for dma-buf pages */
> + size_t num_pages;
> + struct page *pages;
> + struct dev_pagemap pgmap;
> +
> + unsigned int type;
> + const struct dma_buf_pages_type_ops *type_ops;
> + __u64 create_flags;
> +};
> +
> /**
> * DEFINE_DMA_BUF_EXPORT_INFO - helper macro for exporters
> * @name: export-info name
> @@ -631,4 +661,64 @@ int dma_buf_vmap(struct dma_buf *dmabuf, struct iosys_map *map);
> void dma_buf_vunmap(struct dma_buf *dmabuf, struct iosys_map *map);
> int dma_buf_vmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map);
> void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map);
> +
> +#ifdef CONFIG_DMA_SHARED_BUFFER
> +extern const struct file_operations dma_buf_pages_fops;
> +extern const struct dev_pagemap_ops dma_buf_pgmap_ops;
> +
> +static inline bool is_dma_buf_pages_file(struct file *file)
> +{
> + return file->f_op == &dma_buf_pages_fops;
> +}
> +
> +static inline bool is_dma_buf_page(struct page *page)
> +{
> + return (is_zone_device_page(page) && page->pgmap &&
> + page->pgmap->ops == &dma_buf_pgmap_ops);
> +}
> +
> +static inline dma_addr_t dma_buf_page_to_dma_addr(struct page *page)
> +{
> + return (dma_addr_t)page->zone_device_data;
> +}
> +
> +static inline int dma_buf_map_sg(struct device *dev, struct scatterlist *sg,
> + int nents, enum dma_data_direction dir)
> +{
> + struct scatterlist *s;
> + int i;
> +
> + for_each_sg(sg, s, nents, i) {
> + struct page *pg = sg_page(s);
> +
> + s->dma_address = dma_buf_page_to_dma_addr(pg);
> + sg_dma_len(s) = s->length;
> + }
> +
> + return nents;
> +}
> +#else
> +static inline bool is_dma_buf_page(struct page *page)
> +{
> + return false;
> +}
> +
> +static inline bool is_dma_buf_pages_file(struct file *file)
> +{
> + return false;
> +}
> +
> +static inline dma_addr_t dma_buf_page_to_dma_addr(struct page *page)
> +{
> + return 0;
> +}
> +
> +static inline int dma_buf_map_sg(struct device *dev, struct scatterlist *sg,
> + int nents, enum dma_data_direction dir)
> +{
> + return 0;
> +}
> +#endif
> +
> +
> #endif /* __DMA_BUF_H__ */
> diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
> index 5a6fda66d9ad..d0f63a2ab7e4 100644
> --- a/include/uapi/linux/dma-buf.h
> +++ b/include/uapi/linux/dma-buf.h
> @@ -179,4 +179,13 @@ struct dma_buf_import_sync_file {
> #define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)
> #define DMA_BUF_IOCTL_IMPORT_SYNC_FILE _IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file)
>
> +struct dma_buf_create_pages_info {
> + __u8 pci_bdf[3];
> + __s32 dma_buf_fd;
> + __u32 type;
> + __u64 create_flags;
> +};
> +
> +#define DMA_BUF_CREATE_PAGES _IOW(DMA_BUF_BASE, 4, struct dma_buf_create_pages_info)
> +
> #endif
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