Re: [PATCH v3 1/2] s390/vfio-ap: bypass unnecessary processing of AP resources

[Halil Pasic <pasic@linux.ibm.com>]

On Tue, 23 Aug 2022 11:06:42 -0400
Tony Krowiak <akrowiak@linux.ibm.com> wrote:

> It is not necessary to go through the process of validation, linking of
> queues to mdev and vice versa and filtering the APQNs assigned to the
> matrix mdev to build an AP configuration for a guest if an adapter or
> domain being assigned is already assigned to the matrix mdev. Likewise, it
> is not necessary to proceed through the process the unassignment of an
> adapter, domain or control domain if it is not assigned to the matrix mdev.
> 
> Since it is not necessary to process assignment of a resource resource
> already assigned or process unassignment of a resource that is been assigned,
> this patch will bypass all assignment/unassignment operations for an adapter,
> domain or control domain under these circumstances.
> 
> Not only is assignment of a duplicate adapter or domain unnecessary, it
> will also cause a hang situation when removing the matrix mdev to which it is
> assigned. 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 multiple times to the hashtable that holds them.
> 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
> resulting in an interminable loop when the mdev is removed and the queue
> table is iterated to reset the queues.
> 
> Cc: stable@vger.kernel.org
> Fixes: 11cb2419fafe ("s390/vfio-ap: manage link between queue struct and matrix mdev")
> Reported-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>

Reviewed-by: Halil Pasic <pasic@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)) {