From mboxrd@z Thu Jan  1 00:00:00 1970
From: Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [RFC 7/11] virtio_pci: new, capability-aware driver.
Date: Tue, 13 Dec 2011 12:51:20 +1030
Message-ID: <87liqhtdnj.fsf@rustcorp.com.au>
References: <87pqfzgy6p.fsf@rustcorp.com.au> <87zkf3fiu2.fsf@rustcorp.com.au>
	<20111211094256.GB11504@redhat.com>
	<87boreohhs.fsf@rustcorp.com.au>
	<20111212182533.GB25916@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <virtualization-bounces@lists.linux-foundation.org>
In-Reply-To: <20111212182533.GB25916@redhat.com>
List-Unsubscribe: <https://lists.linuxfoundation.org/mailman/options/virtualization>,
	<mailto:virtualization-request@lists.linux-foundation.org?subject=unsubscribe>
List-Archive: <http://lists.linuxfoundation.org/pipermail/virtualization/>
List-Post: <mailto:virtualization@lists.linux-foundation.org>
List-Help: <mailto:virtualization-request@lists.linux-foundation.org?subject=help>
List-Subscribe: <https://lists.linuxfoundation.org/mailman/listinfo/virtualization>,
	<mailto:virtualization-request@lists.linux-foundation.org?subject=subscribe>
Sender: virtualization-bounces@lists.linux-foundation.org
Errors-To: virtualization-bounces@lists.linux-foundation.org
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Sasha Levin <levinsasha928@gmail.com>, virtualization <virtualization@lists.linux-foundation.org>
List-Id: virtualization@lists.linuxfoundation.org

On Mon, 12 Dec 2011 20:25:34 +0200, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> By the way, a generic question on virtio-pci: we now have:
> 
> /* virtio config->get() implementation */
> static void vp_get(struct virtio_device *vdev, unsigned offset,
>                    void *buf, unsigned len)
> {
>         struct virtio_pci_device *vp_dev = to_vp_device(vdev);
>         void __iomem *ioaddr = vp_dev->ioaddr +
>                                 VIRTIO_PCI_CONFIG(vp_dev) + offset;
>         u8 *ptr = buf;
>         int i;
> 
>         for (i = 0; i < len; i++)
>                 ptr[i] = ioread8(ioaddr + i);
> }
> 
> This means that if configuration is read while
> it is changed, we might get an inconsistent state,
> with parts of a 64 bit field coming from old
> and parts from new value.
> 
> Isn't this a problem?

I don't think so; it's the caller's problem if they need to do locking.
Is there a caller which needs this?

Or am I missing something?
Rusty.