io_uring: introduce concept of memory regions

We've got a good number of mappings we share with the userspace, that
includes the main rings, provided buffer rings, upcoming rings for
zerocopy rx and more. All of them duplicate user argument parsing and
some internal details as well (page pinnning, huge page optimisations,
mmap'ing, etc.)

Introduce a notion of regions. For userspace for now it's just a new
structure called struct io_uring_region_desc which is supposed to
parameterise all such mapping / queue creations. A region either
represents a user provided chunk of memory, in which case the user_addr
field should point to it, or a request for the kernel to allocate the
memory, in which case the user would need to mmap it after using the
offset returned in the mmap_offset field. With a uniform userspace API
we can avoid additional boiler plate code and apply future optimisation
to all of them at once.

Internally, there is a new structure struct io_mapped_region holding all
relevant runtime information and some helpers to work with it. This
patch limits it to user provided regions.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0e6fe25818dfbaebd1bd90b870a6cac503fe1a24.1731689588.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/io_uring_types.h

@@ -75,6 +75,12 @@ struct io_hash_table {
 	unsigned		hash_bits;
 };
 
+struct io_mapped_region {
+	struct page		**pages;
+	void			*vmap_ptr;
+	size_t			nr_pages;
+};
+
 /*
  * Arbitrary limit, can be raised if need be
  */

include/uapi/linux/io_uring.h

@@ -647,6 +647,20 @@ struct io_uring_files_update {
 	__aligned_u64 /* __s32 * */ fds;
 };
 
+enum {
+	/* initialise with user provided memory pointed by user_addr */
+	IORING_MEM_REGION_TYPE_USER		= 1,
+};
+
+struct io_uring_region_desc {
+	__u64 user_addr;
+	__u64 size;
+	__u32 flags;
+	__u32 id;
+	__u64 mmap_offset;
+	__u64 __resv[4];
+};
+
 /*
  * Register a fully sparse file space, rather than pass in an array of all
  * -1 file descriptors.

io_uring/memmap.c

@@ -12,6 +12,7 @@
 
 #include "memmap.h"
 #include "kbuf.h"
+#include "rsrc.h"
 
 static void *io_mem_alloc_compound(struct page **pages, int nr_pages,
 				   size_t size, gfp_t gfp)
@@ -194,6 +195,72 @@ void *__io_uaddr_map(struct page ***pages, unsigned short *npages,
 	return ERR_PTR(-ENOMEM);
 }
 
+void io_free_region(struct io_ring_ctx *ctx, struct io_mapped_region *mr)
+{
+	if (mr->pages) {
+		unpin_user_pages(mr->pages, mr->nr_pages);
+		kvfree(mr->pages);
+	}
+	if (mr->vmap_ptr)
+		vunmap(mr->vmap_ptr);
+	if (mr->nr_pages && ctx->user)
+		__io_unaccount_mem(ctx->user, mr->nr_pages);
+
+	memset(mr, 0, sizeof(*mr));
+}
+
+int io_create_region(struct io_ring_ctx *ctx, struct io_mapped_region *mr,
+		     struct io_uring_region_desc *reg)
+{
+	int pages_accounted = 0;
+	struct page **pages;
+	int nr_pages, ret;
+	void *vptr;
+	u64 end;
+
+	if (WARN_ON_ONCE(mr->pages || mr->vmap_ptr || mr->nr_pages))
+		return -EFAULT;
+	if (memchr_inv(&reg->__resv, 0, sizeof(reg->__resv)))
+		return -EINVAL;
+	if (reg->flags != IORING_MEM_REGION_TYPE_USER)
+		return -EINVAL;
+	if (!reg->user_addr)
+		return -EFAULT;
+	if (!reg->size || reg->mmap_offset || reg->id)
+		return -EINVAL;
+	if ((reg->size >> PAGE_SHIFT) > INT_MAX)
+		return E2BIG;
+	if ((reg->user_addr | reg->size) & ~PAGE_MASK)
+		return -EINVAL;
+	if (check_add_overflow(reg->user_addr, reg->size, &end))
+		return -EOVERFLOW;
+
+	pages = io_pin_pages(reg->user_addr, reg->size, &nr_pages);
+	if (IS_ERR(pages))
+		return PTR_ERR(pages);
+
+	if (ctx->user) {
+		ret = __io_account_mem(ctx->user, nr_pages);
+		if (ret)
+			goto out_free;
+		pages_accounted = nr_pages;
+	}
+
+	vptr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
+	if (!vptr)
+		goto out_free;
+
+	mr->pages = pages;
+	mr->vmap_ptr = vptr;
+	mr->nr_pages = nr_pages;
+	return 0;
+out_free:
+	if (pages_accounted)
+		__io_unaccount_mem(ctx->user, pages_accounted);
+	io_pages_free(&pages, nr_pages);
+	return ret;
+}
+
 static void *io_uring_validate_mmap_request(struct file *file, loff_t pgoff,
 					    size_t sz)
 {

io_uring/memmap.h

@@ -22,4 +22,18 @@ unsigned long io_uring_get_unmapped_area(struct file *file, unsigned long addr,
 					 unsigned long flags);
 int io_uring_mmap(struct file *file, struct vm_area_struct *vma);
 
+void io_free_region(struct io_ring_ctx *ctx, struct io_mapped_region *mr);
+int io_create_region(struct io_ring_ctx *ctx, struct io_mapped_region *mr,
+		     struct io_uring_region_desc *reg);
+
+static inline void *io_region_get_ptr(struct io_mapped_region *mr)
+{
+	return mr->vmap_ptr;
+}
+
+static inline bool io_region_is_set(struct io_mapped_region *mr)
+{
+	return !!mr->nr_pages;
+}
+
 #endif