LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Alex Williamson <alex.williamson@redhat.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: kwankhede@nvidia.com, Dong Jia <bjsdjshi@linux.vnet.ibm.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
cohuck@redhat.com
Subject: Re: [PATCH v4 0/2] vfio/mdev: Device namespace protection
Date: Tue, 22 May 2018 12:38:29 -0600 [thread overview]
Message-ID: <20180522123829.4e758646@w520.home> (raw)
In-Reply-To: <c666f6b7-bd49-79e4-703d-2724f7549c53@linux.ibm.com>
On Tue, 22 May 2018 19:17:07 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:
> From vfio-ccw perspective I join Connie's assessment: vfio-ccw should
> be fine with these changes. I'm however not too deeply involved with
> the mdev framework, thus I don't feel comfortable r-b-ing. That results
> in
> Acked-by: Halil Pasic <pasic@linux.ibm.com>
> for both patches.
>
> While at it I have would like to ask about the semantics and intended
> use of the mdev interfaces.
>
> static int vfio_ccw_sch_probe(struct subchannel *sch)
> {
>
> /* HALIL: 8< Not so interesting stuff happens here. >8 */
This was interesting:
private->state = VFIO_CCW_STATE_NOT_OPER;
> ret = vfio_ccw_mdev_reg(sch);
> if (ret)
> goto out_disable;
> /*
> * HALIL:
> * This might be racy. Somewhere in vfio_ccw_mdev_reg() the create attribute
> * is made available (it calls mdev_register_device()). For instance create will
> * attempt to decrement private->avail which is initialized below. I fail to
> * understand how is this well synchronized.
> */
> INIT_WORK(&private->io_work, vfio_ccw_sch_io_todo);
> atomic_set(&private->avail, 1);
> private->state = VFIO_CCW_STATE_STANDBY;
>
> return 0;
>
> out_disable:
> cio_disable_subchannel(sch);
> out_free:
> dev_set_drvdata(&sch->dev, NULL);
> kfree(private);
> return ret;
> }
>
> Should not initialization of go before mdev_register_device(), and then rolled
> back if necessary if mdev_register_device() fails?
>
> In practice it does not seem very likely that userspace can trigger
> mdev_device_create() before vfio_ccw_sch_probe() finishes so it should
> not be a practical problem. But I would like to understand how synchronization
> is supposed to work.
>
> [Added Dong Jia, maybe he is also able to answer my question.]
vfio_ccw_mdev_create() requires that private->state is not
VFIO_CCW_STATE_NOT_OPER but vfio_ccw_sch_probe() explicitly sets state
to this value before calling vfio_ccw_mdev_reg(), so a create should
return -ENODEV if racing with parent registration. Is there something
else that I'm missing? Thanks,
Alex
next prev parent reply other threads:[~2018-05-22 18:38 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-18 19:10 Alex Williamson
2018-05-18 19:10 ` [PATCH v4 1/2] vfio/mdev: Check globally for duplicate devices Alex Williamson
2018-05-18 19:37 ` Kirti Wankhede
2018-05-22 8:13 ` Cornelia Huck
2018-05-22 15:53 ` Alex Williamson
2018-05-23 4:53 ` Zhenyu Wang
2018-05-18 19:10 ` [PATCH v4 2/2] vfio/mdev: Re-order sysfs attribute creation Alex Williamson
2018-05-18 19:38 ` Kirti Wankhede
2018-05-22 8:14 ` Cornelia Huck
2018-05-18 19:37 ` [PATCH v4 0/2] vfio/mdev: Device namespace protection Kirti Wankhede
2018-05-22 17:17 ` Halil Pasic
2018-05-22 18:38 ` Alex Williamson [this message]
2018-05-23 8:56 ` Cornelia Huck
2018-05-23 12:29 ` Halil Pasic
2018-05-23 13:34 ` Cornelia Huck
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=20180522123829.4e758646@w520.home \
--to=alex.williamson@redhat.com \
--cc=bjsdjshi@linux.vnet.ibm.com \
--cc=cohuck@redhat.com \
--cc=kvm@vger.kernel.org \
--cc=kwankhede@nvidia.com \
--cc=linux-kernel@vger.kernel.org \
--cc=pasic@linux.ibm.com \
--subject='Re: [PATCH v4 0/2] vfio/mdev: Device namespace protection' \
/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
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).