linux-kernel - Re: [PATCH RFC 0/3] io_uring: add restrictions to support untrusted applications and guests

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Date:   Fri, 10 Jul 2020 18:20:17 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Sargun Dhillon <sargun@...gun.me>,
        Kees Cook <keescook@...omium.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Jann Horn <jannh@...gle.com>, Aleksa Sarai <asarai@...e.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        io-uring@...r.kernel.org, Alexander Viro <viro@...iv.linux.org.uk>,
        Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH RFC 0/3] io_uring: add restrictions to support untrusted
 applications and guests

Hi Konrad,

On Fri, Jul 10, 2020 at 11:33:09AM -0400, Konrad Rzeszutek Wilk wrote:
> .snip..
> > Just to recap the proposal, the idea is to add some restrictions to the
> > operations (sqe, register, fixed file) to safely allow untrusted applications
> > or guests to use io_uring queues.
> 
> Hi!
> 
> This is neat and quite cool - but one thing that keeps nagging me is
> what how much overhead does this cut from the existing setup when you use
> virtio (with guests obviously)?

I need to do more tests, but the preliminary results that I reported on
the original proposal [1] show an overhead of ~ 4.17 uS (with iodepth=1)
when I'm using virtio ring processed in a dedicated iothread:

  - 73 kIOPS using virtio-blk + QEMU iothread + io_uring backend
  - 104 kIOPS using io_uring passthrough

>                                 That is from a high level view the
> beaty of io_uring being passed in the guest is you don't have the
> virtio ring -> io_uring processing, right?

Right, and potentially we can share the io_uring queues directly to the
guest userspace applications, cutting down the cost of Linux block
layer in the guest.

Thanks for your feedback,
Stefano

[1] https://lore.kernel.org/io-uring/20200609142406.upuwpfmgqjeji4lc@steredhat/