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io_uring: restore back registered wait arguments

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Now we've got a more generic region registration API, place
IORING_ENTER_EXT_ARG_REG and re-enable it.

First, the user has to register a region with the
IORING_MEM_REGION_REG_WAIT_ARG flag set. It can only be done for a
ring in a disabled state, aka IORING_SETUP_R_DISABLED, to avoid races
with already running waiters. With that we should have stable constant
values for ctx->cq_wait_{size,arg} in io_get_ext_arg_reg() and hence no
READ_ONCE required.

The other API difference is that we're now passing byte offsets instead
of indexes. The user _must_ align all offsets / pointers to the native
word size, failing to do so might but not necessarily has to lead to a
failure usually returned as -EFAULT. liburing will be hiding this
details from users.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/81822c1b4ffbe8ad391b4f9ad1564def0d26d990.1731689588.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2024-11-15 16:54:43 +00:00 committed by Jens Axboe
parent 93238e6618
commit d617b3147d
4 changed files with 36 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

3
include/linux/io_uring_types.h
View file

@ -324,6 +324,9 @@ struct io_ring_ctx {
unsigned cq_entries;
struct io_ev_fd __rcu *io_ev_fd;
unsigned cq_extra;
void *cq_wait_arg;
size_t cq_wait_size;
} ____cacheline_aligned_in_smp;
/*

5
include/uapi/linux/io_uring.h
View file

@ -663,6 +663,11 @@ struct io_uring_region_desc {
__u64 __resv[4];
};
enum {
/* expose the region as registered wait arguments */
IORING_MEM_REGION_REG_WAIT_ARG = 1,
};
struct io_uring_mem_region_reg {
__u64 region_uptr; /* struct io_uring_region_desc * */
__u64 flags;

14
io_uring/io_uring.c
View file

@ -3195,7 +3195,19 @@ void __io_uring_cancel(bool cancel_all)
static struct io_uring_reg_wait *io_get_ext_arg_reg(struct io_ring_ctx *ctx,
const struct io_uring_getevents_arg __user *uarg)
{
return ERR_PTR(-EFAULT);
unsigned long size = sizeof(struct io_uring_reg_wait);
unsigned long offset = (uintptr_t)uarg;
unsigned long end;
if (unlikely(offset % sizeof(long)))
return ERR_PTR(-EFAULT);
/* also protects from NULL ->cq_wait_arg as the size would be 0 */
if (unlikely(check_add_overflow(offset, size, &end) ||
end > ctx->cq_wait_size))
return ERR_PTR(-EFAULT);
return ctx->cq_wait_arg + offset;
}
static int io_validate_ext_arg(struct io_ring_ctx *ctx, unsigned flags,

16
io_uring/register.c
View file

@ -588,7 +588,16 @@ static int io_register_mem_region(struct io_ring_ctx *ctx, void __user *uarg)
if (memchr_inv(&reg.__resv, 0, sizeof(reg.__resv)))
return -EINVAL;
if (reg.flags)
if (reg.flags & ~IORING_MEM_REGION_REG_WAIT_ARG)
return -EINVAL;
/*
* This ensures there are no waiters. Waiters are unlocked and it's
* hard to synchronise with them, especially if we need to initialise
* the region.
*/
if ((reg.flags & IORING_MEM_REGION_REG_WAIT_ARG) &&
!(ctx->flags & IORING_SETUP_R_DISABLED))
return -EINVAL;
ret = io_create_region(ctx, &ctx->param_region, &rd);
@ -598,6 +607,11 @@ static int io_register_mem_region(struct io_ring_ctx *ctx, void __user *uarg)
io_free_region(ctx, &ctx->param_region);
return -EFAULT;
}
if (reg.flags & IORING_MEM_REGION_REG_WAIT_ARG) {
ctx->cq_wait_arg = io_region_get_ptr(&ctx->param_region);
ctx->cq_wait_size = rd.size;
}
return 0;
}