linux-kernel - Re: [PATCH v1] s390/vfio-ap: Signal eventfd when guest AP configuration is changed

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Message-ID: <105ff0df576ac86c1cd2edd4e1a6478c@linux.ibm.com>
Date: Fri, 17 Jan 2025 09:30:38 +0100
From: Harald Freudenberger <freude@...ux.ibm.com>
To: Anthony Krowiak <akrowiak@...ux.ibm.com>
Cc: Rorie Reyes <rreyes@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, hca@...ux.ibm.com,
        borntraeger@...ibm.com, agordeev@...ux.ibm.com, gor@...ux.ibm.com,
        pasic@...ux.ibm.com, jjherne@...ux.ibm.com, alex.williamson@...hat.com
Subject: Re: [PATCH v1] s390/vfio-ap: Signal eventfd when guest AP
 configuration is changed

On 2025-01-16 17:46, Anthony Krowiak wrote:
>> 
>> Rorie, this is to inform listeners on the host of the guest.
>> The guest itself already sees this "inside" with uevents triggered
>> by the AP bus code.
>> 
>> Do you have a consumer for these events?
> 
> There is a series of QEMU patches that register a notification handler 
> for this
> event. When that handler gets called, it generates and queues a CRW to 
> the guest
> indicating there is event information pending which will cause the AP 
> bus driver
> to get notified of the AP configuration change via its ap_bus_cfg_chg
> notifier call.
> 
> The QEMU series can be seen at:
> https://lore.kernel.org/qemu-devel/7171c479-5cb4-4748-ba37-da4cf2fac35b@linux.ibm.com/T/
> 
> 
> Kind regards,
> A Krowiak

Ok, so this way the AP bus of the guest finally get's it's config change 
callback invoked :-)