linux-kernel - Re: [PATCH v10 06/16] s390/vfio-ap: introduce shadow APCB

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Date:   Fri, 18 Sep 2020 13:03:55 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ux.ibm.com, borntraeger@...ibm.com,
        mjrosato@...ux.ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        fiuczy@...ux.ibm.com, frankja@...ux.ibm.com, david@...hat.com,
        imbrenda@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v10 06/16] s390/vfio-ap: introduce shadow APCB



On 9/17/20 10:22 AM, Cornelia Huck wrote:
> On Fri, 21 Aug 2020 15:56:06 -0400
> Tony Krowiak <akrowiak@...ux.ibm.com> wrote:
>
>> The APCB is a field within the CRYCB that provides the AP configuration
>> to a KVM guest. Let's introduce a shadow copy of the KVM guest's APCB and
>> maintain it for the lifespan of the guest.
>>
>> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
>> ---
>>   drivers/s390/crypto/vfio_ap_ops.c     | 32 ++++++++++++++++++++++-----
>>   drivers/s390/crypto/vfio_ap_private.h |  2 ++
>>   2 files changed, 29 insertions(+), 5 deletions(-)
> (...)
>
>> @@ -1202,13 +1223,12 @@ static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
>>   	if (ret)
>>   		return NOTIFY_DONE;
>>   
>> -	/* If there is no CRYCB pointer, then we can't copy the masks */
>> -	if (!matrix_mdev->kvm->arch.crypto.crycbd)
>> +	if (!vfio_ap_mdev_has_crycb(matrix_mdev))
>>   		return NOTIFY_DONE;
>>   
>> -	kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm,
>> -				  matrix_mdev->matrix.aqm,
>> -				  matrix_mdev->matrix.adm);
>> +	memcpy(&matrix_mdev->shadow_apcb, &matrix_mdev->matrix,
>> +	       sizeof(matrix_mdev->shadow_apcb));
>> +	vfio_ap_mdev_commit_crycb(matrix_mdev);
> We are sure that the shadow APCB always matches up as we are the only
> ones manipulating the APCB in the CRYCB, right?

Yes

>
>>   
>>   	return NOTIFY_OK;
>>   }