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Message-ID: <4e89ff00-aac2-7c8e-14cf-add426853e9d@de.ibm.com>
Date:   Thu, 15 Sep 2022 16:53:51 +0200
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Subject: Re: [PATCH v3 1/2] s390/vfio-ap: bypass unnecessary processing of AP
 resources
Content-Language: en-US
To:     Halil Pasic <pasic@linux.ibm.com>,
        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, cohuck@redhat.com,
        mjrosato@linux.ibm.com, alex.williamson@redhat.com,
        stable@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>
References: <20220823150643.427737-1-akrowiak@linux.ibm.com>
 <20220823150643.427737-2-akrowiak@linux.ibm.com>
 <20220915050018.37d21083.pasic@linux.ibm.com>
From:   Christian Borntraeger <borntraeger@de.ibm.com>
In-Reply-To: <20220915050018.37d21083.pasic@linux.ibm.com>
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Am 15.09.22 um 05:00 schrieb Halil Pasic:
> 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>

Shall the patch go via the s390 tree (still into 6.0 I guess)?

> 
>> ---
>>   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)) {
>