From: Jens Axboe <axboe@kernel.dk>
To: Jann Horn <jannh@google.com>
Cc: linux-aio@kvack.org, linux-block@vger.kernel.org,
Linux API <linux-api@vger.kernel.org>,
hch@lst.de, jmoyer@redhat.com, Avi Kivity <avi@scylladb.com>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 12/19] io_uring: add support for pre-mapped user IO buffers
Date: Fri, 8 Feb 2019 16:38:19 -0700 [thread overview]
Message-ID: <2ef04b12-6a4b-af25-cbf8-9dde79b0ec1e@kernel.dk> (raw)
In-Reply-To: <CAG48ez0uH_muHobzpwFzdyBWCcWDxbnfpuxABntph6Te+tYxGg@mail.gmail.com>
On 2/8/19 3:54 PM, Jann Horn wrote:
> On Fri, Feb 8, 2019 at 6:35 PM Jens Axboe <axboe@kernel.dk> wrote:
>> If we have fixed user buffers, we can map them into the kernel when we
>> setup the io_uring. That avoids the need to do get_user_pages() for
>> each and every IO.
>>
>> To utilize this feature, the application must call io_uring_register()
>> after having setup an io_uring instance, passing in
>> IORING_REGISTER_BUFFERS as the opcode. The argument must be a pointer to
>> an iovec array, and the nr_args should contain how many iovecs the
>> application wishes to map.
>>
>> If successful, these buffers are now mapped into the kernel, eligible
>> for IO. To use these fixed buffers, the application must use the
>> IORING_OP_READ_FIXED and IORING_OP_WRITE_FIXED opcodes, and then
>> set sqe->index to the desired buffer index. sqe->addr..sqe->addr+seq->len
>> must point to somewhere inside the indexed buffer.
>>
>> The application may register buffers throughout the lifetime of the
>> io_uring instance. It can call io_uring_register() with
>> IORING_UNREGISTER_BUFFERS as the opcode to unregister the current set of
>> buffers, and then register a new set. The application need not
>> unregister buffers explicitly before shutting down the io_uring
>> instance.
>>
>> It's perfectly valid to setup a larger buffer, and then sometimes only
>> use parts of it for an IO. As long as the range is within the originally
>> mapped region, it will work just fine.
>>
>> For now, buffers must not be file backed. If file backed buffers are
>> passed in, the registration will fail with -1/EOPNOTSUPP. This
>> restriction may be relaxed in the future.
>>
>> RLIMIT_MEMLOCK is used to check how much memory we can pin. A somewhat
>> arbitrary 1G per buffer size is also imposed.
> [...]
>> static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
>> const struct sqe_submit *s, struct iovec **iovec,
>> struct iov_iter *iter)
>> @@ -711,6 +763,15 @@ static int io_import_iovec(struct io_ring_ctx *ctx, int rw,
>> const struct io_uring_sqe *sqe = s->sqe;
>> void __user *buf = u64_to_user_ptr(READ_ONCE(sqe->addr));
>> size_t sqe_len = READ_ONCE(sqe->len);
>> + u8 opcode;
>
> (You could add a comment here if you want, something like "We're
> reading ->opcode for the second time, but the first read doesn't care
> whether it's _FIXED or not, so it doesn't matter whether ->opcode
> changes concurrently. The first read does care about whether it is a
> READ or a WRITE, so we don't trust this read for that purpose and
> instead let the caller pass in the read/write flag.")
Sure, I can add that.
>> +static int io_sqe_buffer_unregister(struct io_ring_ctx *ctx)
>> +{
>> + int i, j;
>> +
>> + if (!ctx->user_bufs)
>> + return -ENXIO;
>> +
>> + for (i = 0; i < ctx->sq_entries; i++) {
>
> ->sq_entries? Shouldn't this be ->nr_user_bufs?
It should! I swear I already fixed that, odd. Maybe that was somewhere
else...
>> + struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
>> +
>> + for (j = 0; j < imu->nr_bvecs; j++)
>> + put_page(imu->bvec[j].bv_page);
>> +
>> + io_unaccount_mem(ctx->user, imu->nr_bvecs);
>> + kfree(imu->bvec);
>> + imu->nr_bvecs = 0;
>> + }
>> +
>> + kfree(ctx->user_bufs);
>> + ctx->user_bufs = NULL;
>
> (It isn't really necessary, but you could set nr_user_bufs=0 here.)
Doesn't hurt to be defensive.
>> + return 0;
>> +}
> [...]
>> +static int io_sqe_buffer_register(struct io_ring_ctx *ctx, void __user *arg,
>> + unsigned nr_args)
>> +{
>> + struct vm_area_struct **vmas = NULL;
>> + struct page **pages = NULL;
>> + int i, j, got_pages = 0;
>> + int ret = -EINVAL;
>> +
>> + if (ctx->user_bufs)
>> + return -EBUSY;
>> + if (!nr_args || nr_args > UIO_MAXIOV)
>> + return -EINVAL;
>> +
>> + ctx->user_bufs = kcalloc(nr_args, sizeof(struct io_mapped_ubuf),
>> + GFP_KERNEL);
>> + if (!ctx->user_bufs)
>> + return -ENOMEM;
>> +
>> + for (i = 0; i < nr_args; i++) {
>> + struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
>> + unsigned long off, start, end, ubuf;
>> + int pret, nr_pages;
>> + struct iovec iov;
>> + size_t size;
>> +
>> + ret = io_copy_iov(ctx, &iov, arg, i);
>> + if (ret)
>> + break;
>> +
>> + /*
>> + * Don't impose further limits on the size and buffer
>> + * constraints here, we'll -EINVAL later when IO is
>> + * submitted if they are wrong.
>> + */
>> + ret = -EFAULT;
>> + if (!iov.iov_base || !iov.iov_len)
>> + goto err;
>> +
>> + /* arbitrary limit, but we need something */
>> + if (iov.iov_len > SZ_1G)
>> + goto err;
>> +
>> + ubuf = (unsigned long) iov.iov_base;
>> + end = (ubuf + iov.iov_len + PAGE_SIZE - 1) >> PAGE_SHIFT;
>> + start = ubuf >> PAGE_SHIFT;
>> + nr_pages = end - start;
>> +
>> + ret = io_account_mem(ctx->user, nr_pages);
>
> Technically, this accounting is probably a bit off; I think if you
> pass in a vector of 4K areas from 1G hugepages, you're going to pin
> factor 0x40000 more memory than you think you're pinning.
> (get_user_pages() counts references against the head page of a
> compound page; nothing in the kernel can tell afterwards which part of
> the hugepage you're using.) I'm not sure how much of a problem that
> is, but it should probably at least be documented. Unless I'm just
> missing something?
No I think you are right, it doesn't account for the hugepage size if
you pass in huge pages. I'll fix that up.
>> + if (ret)
>> + goto err;
>> +
>> + if (!pages || nr_pages > got_pages) {
>> + kfree(vmas);
>> + kfree(pages);
>> + pages = kmalloc_array(nr_pages, sizeof(struct page *),
>> + GFP_KERNEL);
>> + vmas = kmalloc_array(nr_pages,
>> + sizeof(struct vma_area_struct *),
>> + GFP_KERNEL);
>> + if (!pages || !vmas) {
>> + ret = -ENOMEM;
>> + io_unaccount_mem(ctx->user, nr_pages);
>> + goto err;
>> + }
>> + got_pages = nr_pages;
>> + }
>> +
>> + imu->bvec = kmalloc_array(nr_pages, sizeof(struct bio_vec),
>> + GFP_KERNEL);
>> + if (!imu->bvec) {
>> + io_unaccount_mem(ctx->user, nr_pages);
>> + goto err;
>> + }
>> +
>> + down_write(¤t->mm->mmap_sem);
>
> Weren't you planning to make this down_read()?
I think I accidentally messed that up when going back to not using
FOLL_ANON. Fixed (again), thanks.
>> + pret = get_user_pages_longterm(ubuf, nr_pages, FOLL_WRITE,
>> + pages, vmas);
>> + if (pret == nr_pages) {
>> + /* don't support file backed memory */
>> + for (j = 0; j < nr_pages; j++) {
>> + struct vm_area_struct *vma = vmas[j];
>> +
>> + if (vma->vm_file &&
>> + !is_file_hugepages(vma->vm_file)) {
>> + ret = -EOPNOTSUPP;
>> + break;
>> + }
>> + }
>> + } else {
>> + ret = pret < 0 ? pret : -EFAULT;
>> + }
>> + up_write(¤t->mm->mmap_sem);
> [...]
>> +}
> [...]
>> diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
>> index 39ad98c09c58..c7b5f86b91a1 100644
>> --- a/include/linux/sched/user.h
>> +++ b/include/linux/sched/user.h
>> @@ -40,7 +40,7 @@ struct user_struct {
>> kuid_t uid;
>>
>> #if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_BPF_SYSCALL) || \
>> - defined(CONFIG_NET)
>> + defined(CONFIG_NET) || defined(CONFIG_IO_URING)
>> atomic_long_t locked_vm;
>> #endif
>
> You're already using locked_vm in patch 5, right? I think that means
> that from patch 5 up to this patch, some kernel configs will fail to
> build.
Good point, I need to do this earlier now.
--
Jens Axboe
next prev parent reply other threads:[~2019-02-08 23:38 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-08 17:34 [PATCHSET v13] io_uring IO interface Jens Axboe
2019-02-08 17:34 ` [PATCH 01/19] fs: add an iopoll method to struct file_operations Jens Axboe
2019-02-09 9:20 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 02/19] block: wire up block device iopoll method Jens Axboe
2019-02-09 9:22 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 03/19] block: add bio_set_polled() helper Jens Axboe
2019-02-09 9:24 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 04/19] iomap: wire up the iopoll method Jens Axboe
2019-02-09 9:25 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 05/19] Add io_uring IO interface Jens Axboe
2019-02-08 22:12 ` Jann Horn
2019-02-09 4:15 ` Jens Axboe
2019-02-12 21:42 ` Jann Horn
2019-02-12 22:03 ` Jens Axboe
2019-02-12 22:06 ` Jens Axboe
2019-02-12 22:40 ` Jann Horn
2019-02-12 22:45 ` Jens Axboe
2019-02-12 22:52 ` Jens Axboe
2019-02-12 22:57 ` Jann Horn
2019-02-12 23:00 ` Jens Axboe
2019-02-12 23:11 ` Jann Horn
2019-02-12 23:19 ` Jens Axboe
2019-02-12 23:28 ` Jann Horn
2019-02-12 23:46 ` Jens Axboe
2019-02-12 23:53 ` Jens Axboe
2019-02-13 0:07 ` Andy Lutomirski
2019-02-13 0:14 ` Jann Horn
2019-02-13 0:24 ` Jens Axboe
2019-02-09 9:35 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 06/19] io_uring: add fsync support Jens Axboe
2019-02-08 22:36 ` Jann Horn
2019-02-08 23:31 ` Jens Axboe
2019-02-09 9:37 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 07/19] io_uring: support for IO polling Jens Axboe
2019-02-09 9:39 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 08/19] fs: add fget_many() and fput_many() Jens Axboe
2019-02-09 9:41 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 09/19] io_uring: use fget/fput_many() for file references Jens Axboe
2019-02-09 9:42 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 10/19] io_uring: batch io_kiocb allocation Jens Axboe
2019-02-09 9:43 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 11/19] block: implement bio helper to add iter bvec pages to bio Jens Axboe
2019-02-09 9:45 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 12/19] io_uring: add support for pre-mapped user IO buffers Jens Axboe
2019-02-08 22:54 ` Jann Horn
2019-02-08 23:38 ` Jens Axboe [this message]
2019-02-09 16:50 ` Jens Axboe
2019-02-09 9:48 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 13/19] net: split out functions related to registering inflight socket files Jens Axboe
2019-02-08 19:49 ` David Miller
2019-02-08 19:51 ` Jens Axboe
2019-02-09 9:49 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 14/19] io_uring: add file set registration Jens Axboe
2019-02-08 20:26 ` Jann Horn
2019-02-09 0:16 ` Jens Axboe
2019-02-09 9:50 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 15/19] io_uring: add submission polling Jens Axboe
2019-02-09 9:53 ` Hannes Reinecke
2019-02-08 17:34 ` [PATCH 16/19] io_uring: add io_kiocb ref count Jens Axboe
2019-02-08 17:34 ` [PATCH 17/19] io_uring: add support for IORING_OP_POLL Jens Axboe
2019-02-08 17:34 ` [PATCH 18/19] io_uring: allow workqueue item to handle multiple buffered requests Jens Axboe
2019-02-08 17:34 ` [PATCH 19/19] io_uring: add io_uring_event cache hit information Jens Axboe
2019-02-09 21:13 [PATCHSET v14] io_uring IO interface Jens Axboe
2019-02-09 21:13 ` [PATCH 12/19] io_uring: add support for pre-mapped user IO buffers Jens Axboe
2019-02-11 19:00 [PATCHSET v15] io_uring IO interface Jens Axboe
2019-02-11 19:00 ` [PATCH 12/19] io_uring: add support for pre-mapped user IO buffers Jens Axboe
2019-02-19 19:08 ` Jann Horn
2019-02-22 22:29 ` Jens Axboe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=2ef04b12-6a4b-af25-cbf8-9dde79b0ec1e@kernel.dk \
--to=axboe@kernel.dk \
--cc=avi@scylladb.com \
--cc=hch@lst.de \
--cc=jannh@google.com \
--cc=jmoyer@redhat.com \
--cc=linux-aio@kvack.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-block@vger.kernel.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).