linux-kernel - Re: [PATCH v5] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated

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Message-ID: <0649ba1e-ecd3-890a-72b5-a8ff54417faf@de.ibm.com>
Date:   Fri, 22 Jan 2021 09:26:06 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     stable@...r.kernel.org, cohuck@...hat.com, kwankhede@...dia.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pasic@...ux.vnet.ibm.com, Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH v5] s390/vfio-ap: clean up vfio_ap resources when KVM
 pointer invalidated

On 23.12.20 02:20, Tony Krowiak wrote:
> The vfio_ap device driver registers a group notifier with VFIO when the
> file descriptor for a VFIO mediated device for a KVM guest is opened to
> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> event). When the KVM pointer is set, the vfio_ap driver takes the
> following actions:
> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
>    of the mediated device.
> 2. Calls the kvm_get_kvm() function to increment its reference counter.
> 3. Sets the function pointer to the function that handles interception of
>    the instruction that enables/disables interrupt processing.
> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
>    the guest.
> 
> In order to avoid memory leaks, when the notifier is called to receive
> notification that the KVM pointer has been set to NULL, the vfio_ap device
> driver should reverse the actions taken when the KVM pointer was set.
> 
> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> Cc: stable@...r.kernel.org
> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> Reviewed-by: Halil Pasic <pasic@...ux.ibm.com>
> Reviewed-by: Cornelia Huck <cohuck@...hat.com>


Just to keep you up2date why this patch is still waiting in our queue. This triggered
a lockdep splat in the CI which we want to fix first.