linux-kernel - Re: [PATCH v2 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET

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Date:   Thu, 19 May 2022 12:35:00 -0400
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>, jgg@...dia.com,
        alex.williamson@...hat.com
Cc:     cohuck@...hat.com, borntraeger@...ux.ibm.com,
        jjherne@...ux.ibm.com, pasic@...ux.ibm.com,
        zhenyuw@...ux.intel.com, zhi.a.wang@...el.com, hch@...radead.org,
        intel-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

On 5/19/22 12:23 PM, Tony Krowiak wrote:
> I made a few comments, but other than that this looks good to
> me:
> 
> Reviewed-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> 

...

> I'm not sure what version of the code on which the patch was rebased, 

Was on top of Jason's vfio_group_locking series, but now would apply on 
vfio-next since Alex pulled that series in to vfio-next.

> but in the
> latest master branch from our repository the kvm_get_kvm(kvm) function is
> called inside of the if block below. I'm fine with moving outside of the 
> block, but
> I don't see a corresponding removal of it from inside the block.

Yeah, I didn't notice those there.  v3 will simply remove my get/put 
additions and leave yours as-is.

...

>> vfio_ap_mdev_group_notifier;
>> -    events = VFIO_GROUP_NOTIFY_SET_KVM;
>> +    if (!vdev->kvm)
>> +        return -EPERM;
> 
> Perhaps -EINVAL or -EFAULT?
> 

Whichever you'd prefer?  If I don't hear back I'll just use -EINVAL in v3.

>> -    ret = vfio_register_notifier(vdev, VFIO_GROUP_NOTIFY, &events,
>> -                     &matrix_mdev->group_notifier);
>> +    ret = vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm);
>>       if (ret)
>>           return ret;
>> @@ -1415,12 +1400,11 @@ static int vfio_ap_mdev_open_device(struct 
>> vfio_device *vdev)
>>       ret = vfio_register_notifier(vdev, VFIO_IOMMU_NOTIFY, &events,
>>                        &matrix_mdev->iommu_notifier);
>>       if (ret)
>> -        goto out_unregister_group;
>> +        goto err_kvm;
>>       return 0;
>> -out_unregister_group:
>> -    vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
>> -                 &matrix_mdev->group_notifier);
>> +err_kvm:
>> +    vfio_ap_mdev_unset_kvm(matrix_mdev);
>>       return ret;
>>   }
>> @@ -1431,8 +1415,6 @@ static void vfio_ap_mdev_close_device(struct 
>> vfio_device *vdev)
>>       vfio_unregister_notifier(vdev, VFIO_IOMMU_NOTIFY,
>>                    &matrix_mdev->iommu_notifier);
>> -    vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
>> -                 &matrix_mdev->group_notifier);
>>       vfio_ap_mdev_unset_kvm(matrix_mdev);
> 
> I'm not sure if this matters, but the vfio_ap_mdev_unset_kvm(matrix_mdev)
> function uses the KVM pointer stored in matrix_mdev->kvm. I can't imagine
> the KVM pointer stored in vdev->kvm being different than matrix_mdev->kvm,

With this patch matrix_mdev->kvm is set from the value in vdev->kvm 
during vfio_ap_mdev_set_kvm (basically, doing the work that the notifier 
was doing but instead of getting it from notifier data get it from the 
vfio_device)

> but thought I should point it out. Previously, this function was called 
> by the
> notifier handler which did not have access to the KVM pointer which is 
> why it
> was retrieved from matrix_mdev->kvm. Even if the vdev->kvm and
> matrix_mdev->kvm did not match, we should probably go ahead and call
> the unset function anyway to remove access to AP resources for the guest 
> and
> reset the queues.
>