Re: [Qemu-devel] [PATCH v3 01/39] virtio-pci: get config on init

[Michael S. Tsirkin]

On Mon, Aug 08, 2011 at 08:02:08AM -0500, Anthony Liguori wrote:
> On 08/08/2011 07:56 AM, Michael S. Tsirkin wrote:
> >On Mon, Aug 08, 2011 at 07:45:19AM -0500, Anthony Liguori wrote:
> >>On 08/08/2011 05:36 AM, Michael S. Tsirkin wrote:
> >>>>Thinking more closely, I don't think this right.
> >>>>
> >>>>Updating on map ensured that the config was refreshed after each
> >>>>time the bar was mapped.  In the very least, the config needs to be
> >>>>refreshed during reset because the guest may write to the guest
> >>>>space which should get cleared after reset.
> >>>>
> >>>>Regards,
> >>>>
> >>>>Anthony Liguori
> >>>
> >>>Not sure I understand. Which register, for example,
> >>>do you have in mind?
> >>>Could you clarify please?
> >>
> >>Actually, you never need to call config_get() AFAICT.  It's called
> >>in every read/write access.
> >
> >Every read, yes. But every write? Are you sure?
> 
> Yeah, not on write, but I think this is a bug.  get_config() should
> be called before doing the memcpy() in order to have a proper RMW.
> 
> Regards,
> 
> Anthony Liguori

Probably not noticeable because guests don't do the RMW
in practice.
We also send the config over on migration.
That's probably a bug as well ...

-- 
MST