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Date:   Thu, 18 Aug 2022 16:12:55 +0200
From:   Halil Pasic <pasic@linux.ibm.com>
To:     Tony Krowiak <akrowiak@linux.ibm.com>
Cc:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, jjherne@linux.ibm.com, borntraeger@de.ibm.com,
        cohuck@redhat.com, mjrosato@linux.ibm.com,
        alex.williamson@redhat.com, kwankhede@nvidia.com,
        fiuczy@linux.ibm.com, stable@vger.kernel.org,
        Halil Pasic <pasic@linux.ibm.com>
Subject: Re: [PATCH v2 1/2] s390/vfio-ap: fix hang during removal of mdev
 after duplicate assignment
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In-Reply-To: <20220818132606.13321-2-akrowiak@linux.ibm.com>
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        <20220818132606.13321-2-akrowiak@linux.ibm.com>
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On Thu, 18 Aug 2022 09:26:05 -0400
Tony Krowiak <akrowiak@linux.ibm.com> wrote:

Subject: s390/vfio-ap: fix hang during removal of mdev after duplicate
assignment

It would have made sense to do it this way in the first place, even
if the link code were to take care of the duplicates. It did not really
make sense to do the whole filtering biz and everything else. Maybe we
should spin the short description and the rest of the commit message so
it reflects the code more. 

> When the same adapter or domain is assigned more than one time prior to
> removing the matrix mdev to which it is assigned, the remove operation
> will hang. The reason is because the same vfio_ap_queue objects with an
> APQN containing the APID of the adapter or APQI of the domain being
> assigned will get added to the hashtable that holds them multiple times.
> This results in the pprev and next pointers of the hlist_node (mdev_qnode
> field in the vfio_ap_queue object) pointing to the queue object itself.
> This causes an interminable loop when the mdev is removed and the queue
> table is iterated to reset the queues.
> 
> To fix this problem, the assignment operation is bypassed when assigning
> an adapter or domain if it is already assigned to the matrix mdev.
> 
> Since it is not necessary to assign a resource already assigned or to
> unassign a resource that has not been assigned, this patch will bypass
> all assignment/unassignment operations for an adapter, domain or
> control domain under these circumstances.
> 
> Cc: stable@vger.kernel.org
> Fixes: 771e387d5e79 ("s390/vfio-ap: manage link between queue struct and matrix mdev")

Not 11cb2419fafe ("s390/vfio-ap: manage link between queue struct and
matrix mdev")

Is my repo borked?


> Reported-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
>  drivers/s390/crypto/vfio_ap_ops.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index 6c8c41fac4e1..ee82207b4e60 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -984,6 +984,11 @@ static ssize_t assign_adapter_store(struct device *dev,
>  		goto done;
>  	}
>  
> +	if (test_bit_inv(apid, matrix_mdev->matrix.apm)) {
> +		ret = count;
> +		goto done;
> +	}
> +
>  	set_bit_inv(apid, matrix_mdev->matrix.apm);
>  
>  	ret = vfio_ap_mdev_validate_masks(matrix_mdev);
> @@ -1109,6 +1114,11 @@ static ssize_t unassign_adapter_store(struct device *dev,
>  		goto done;
>  	}
>  
> +	if (!test_bit_inv(apid, matrix_mdev->matrix.apm)) {
> +		ret = count;
> +		goto done;
> +	}
> +
>  	clear_bit_inv((unsigned long)apid, matrix_mdev->matrix.apm);
>  	vfio_ap_mdev_hot_unplug_adapter(matrix_mdev, apid);
>  	ret = count;
> @@ -1183,6 +1193,11 @@ static ssize_t assign_domain_store(struct device *dev,
>  		goto done;
>  	}
>  
> +	if (test_bit_inv(apqi, matrix_mdev->matrix.aqm)) {
> +		ret = count;
> +		goto done;
> +	}
> +
>  	set_bit_inv(apqi, matrix_mdev->matrix.aqm);
>  
>  	ret = vfio_ap_mdev_validate_masks(matrix_mdev);
> @@ -1286,6 +1301,11 @@ static ssize_t unassign_domain_store(struct device *dev,
>  		goto done;
>  	}
>  
> +	if (!test_bit_inv(apqi, matrix_mdev->matrix.aqm)) {
> +		ret = count;
> +		goto done;
> +	}
> +
>  	clear_bit_inv((unsigned long)apqi, matrix_mdev->matrix.aqm);
>  	vfio_ap_mdev_hot_unplug_domain(matrix_mdev, apqi);
>  	ret = count;
> @@ -1329,6 +1349,11 @@ static ssize_t assign_control_domain_store(struct device *dev,
>  		goto done;
>  	}
>  
> +	if (test_bit_inv(id, matrix_mdev->matrix.adm)) {
> +		ret = count;
> +		goto done;
> +	}
> +
>  	/* Set the bit in the ADM (bitmask) corresponding to the AP control
>  	 * domain number (id). The bits in the mask, from most significant to
>  	 * least significant, correspond to IDs 0 up to the one less than the
> @@ -1378,6 +1403,11 @@ static ssize_t unassign_control_domain_store(struct device *dev,
>  		goto done;
>  	}
>  
> +	if (!test_bit_inv(domid, matrix_mdev->matrix.adm)) {
> +		ret = count;
> +		goto done;
> +	}
> +
>  	clear_bit_inv(domid, matrix_mdev->matrix.adm);
>  
>  	if (test_bit_inv(domid, matrix_mdev->shadow_apcb.adm)) {