Linux-Block Archive on lore.kernel.org
 help / color / Atom feed
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
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(&current->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(&current->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


  reply index

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 publically 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

Linux-Block Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-block/0 linux-block/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-block linux-block/ https://lore.kernel.org/linux-block \
		linux-block@vger.kernel.org linux-block@archiver.kernel.org
	public-inbox-index linux-block


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-block


AGPL code for this site: git clone https://public-inbox.org/ public-inbox