linux-kernel - Re: [PATCH 0/3] s390/vfio-ap: fix hang when mdev attached to guest is removed

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Date:   Thu, 1 Jun 2023 08:15:27 -0400
From:   Anthony Krowiak <akrowiak@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, alex.williamson@...hat.com
Cc:     jjherne@...ux.ibm.com, pasic@...ux.ibm.com, farman@...ux.ibm.com,
        borntraeger@...ux.ibm.com, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        "agordeev@...ux.ibm.com" <agordeev@...ux.ibm.com>
Subject: Re: [PATCH 0/3] s390/vfio-ap: fix hang when mdev attached to guest is
 removed



On 5/31/23 10:48 AM, Matthew Rosato wrote:
> On 5/30/23 6:35 PM, Tony Krowiak wrote:
>> When a user attempts to remove a vfio-ap mediated device attached to a
>> guest, the operation hangs until the mdev's fd is closed by the guest
>> (i.e., the hostdev is detached or the guest is shut down). This patch
>> series provides kernel-side code that allows userspace to set up a
>> communication channel that will allow the vfio_ap device driver to notify
>> userspace when a request to release the mdev is received, so that userspace
>> can close the mdev fd and avoid the hang. The patch series provides the
>> following:
>>
>> 1. Introduces code to handle the VFIO_DEVICE_GET_IRQ_INFO and
>>     VFIO_DEVICE_SET_IRQS ioctl calls to set the eventfd_ctx for signaling a
>>     device request to userspace.
>>
>> 2. Wires up the VFIO bus driver callback to request a release of the mdev.
>>     When invoked, the vfio_ap device driver will use the eventfd_ctx set up
>>     in #1 to signal a request to userspace to release the mdev.
>>
>>
>> Note:
>> ----
>> If a user subsequently attempts to restart the guest or re-attach the mdev,
>> the operation will fail with a message indicating the domain is already
>> active. This is a libvirt problem resolved with the following commit:
>>
>> commit ebd004a03dbd ("security: do not remember/recall labels for VFIO
>> MDEVs")
> 
> For the series:
> 
> Reviewed-by: Matthew Rosato <mjrosato@...ux.ibm.com>

Thanks for the review.

> 
> 
> I also did some testing using the companion qemu series at
> https://lore.kernel.org/qemu-devel/20230530225544.280031-1-akrowiak@linux.ibm.com

Shall I credit you with Tested-by also?

> 
> Before kernel+qemu changes:
> 1. mdevctl start -u <uuid>, where <uuid> references a vfio-ap mdev
> 2. start a qemu guest with <uuid> attached
> 3. mdvectl stop -u <uuid>
> 4. -mdevctl will now hang indefinitely; the mdev remains in-use by the guest-
> Note: detaching the device or powering off the guest will allow the mdevctl command to complete.
> 
> After kernel+qemu changes:
> 1. mdevctl start -u <uuid>, where <uuid> references a vfio-ap mdev
> 2. start a qemu guest with <uuid> attached
> 3. mdvectl stop -u <uuid>
> 4. -device is detached from the guest and stopped-
> 5. Using a libvirt that includes ebd004a03dbd I also verified that the mdev can be started again and re-attached to the running guest without error.
> 
> 
>>
>> Tony Krowiak (3):
>>    vfio: ap: realize the VFIO_DEVICE_GET_IRQ_INFO ioctl
>>    vfio: ap: realize the VFIO_DEVICE_SET_IRQS ioctl
>>    s390/vfio-ap: Wire in the vfio_device_ops request callback
>>
>>   drivers/s390/crypto/vfio_ap_ops.c     | 134 +++++++++++++++++++++++++-
>>   drivers/s390/crypto/vfio_ap_private.h |   3 +
>>   include/uapi/linux/vfio.h             |   9 ++
>>   3 files changed, 145 insertions(+), 1 deletion(-)
>>
>