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Re: [qemu-s390x] [Qemu-devel] [PATCH v2 2/5] vfio-ccw: concurrent I/O ha

From: Pierre Morel
Subject: Re: [qemu-s390x] [Qemu-devel] [PATCH v2 2/5] vfio-ccw: concurrent I/O handling
Date: Thu, 24 Jan 2019 12:18:11 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

On 24/01/2019 11:19, Cornelia Huck wrote:
On Thu, 24 Jan 2019 11:08:02 +0100
Pierre Morel <address@hidden> wrote:

On 23/01/2019 11:21, Cornelia Huck wrote:
On Tue, 22 Jan 2019 19:33:46 +0100
Halil Pasic <address@hidden> wrote:
On Mon, 21 Jan 2019 12:03:51 +0100
Cornelia Huck <address@hidden> wrote:
--- a/drivers/s390/cio/vfio_ccw_private.h
+++ b/drivers/s390/cio/vfio_ccw_private.h
@@ -28,6 +28,7 @@
    * @mdev: pointer to the mediated device
    * @nb: notifier for vfio events
    * @io_region: MMIO region to input/output I/O arguments/results
+ * @io_mutex: protect against concurrent update of I/O structures

We could be a bit more specific about what does this mutex guard.
Is it only io_region, or cp, irb and the new regions a well? ->state does
not seem to be covered, but should need some sort of synchronisation
too, or?

I'm not sure. IIRC Pierre had some ideas about locking in the fsm?

Yes I postponed this work to not collide with your patch series.

Do you think I should provide a new version of the FSM reworking series
based on the last comment I got?

I would take into account that the asynchronous commands will come with
your patch series and only provide the framework changes.

This was more an answer to Halil's concerns around state
synchronization. I would prefer to first get this series (or a
variation) into decent shape, and then address state machine handling
on top of that (when we know more about the transitions involved), just
to avoid confusion.

Does that sound reasonable?

Absolutely, this was why I waited with my series. :)

Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany

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