linux-kernel - Re: [PATCH v11 11/26] s390: vfio-ap: implement mediated device open callback

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Date:   Fri, 28 Sep 2018 09:02:20 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        kwankhede@...dia.com, bjsdjshi@...ux.vnet.ibm.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pmorel@...ux.vnet.ibm.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com,
        frankja@...ux.ibm.com
Subject: Re: [PATCH v11 11/26] s390: vfio-ap: implement mediated device open
 callback

On 09/28/2018 06:14 AM, Cornelia Huck wrote:
> On Tue, 25 Sep 2018 19:16:26 -0400
> Tony Krowiak <akrowiak@...ux.vnet.ibm.com> wrote:
> 
>> From: Tony Krowiak <akrowiak@...ux.ibm.com>
>>
>> Implements the open callback on the mediated matrix device.
>> The function registers a group notifier to receive notification
>> of the VFIO_GROUP_NOTIFY_SET_KVM event. When notified,
>> the vfio_ap device driver will get access to the guest's
>> kvm structure. The open callback must ensure that only one
>> mediated device shall be opened per guest.
>>
>> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
>> Acked-by: Halil Pasic <pasic@...ux.ibm.com>
>> Tested-by: Michael Mueller <mimu@...ux.ibm.com>
>> Tested-by: Farhan Ali <alifm@...ux.ibm.com>
>> Tested-by: Pierre Morel <pmorel@...ux.ibm.com>
>> Acked-by: Pierre Morel <pmorel@...ux.ibm.com>
>> ---
>>   arch/s390/include/asm/kvm_host.h      |   1 +
>>   drivers/s390/crypto/vfio_ap_ops.c     | 159 ++++++++++++++++++++++++++
>>   drivers/s390/crypto/vfio_ap_private.h |   5 +
>>   3 files changed, 165 insertions(+)
>>
> 
>> +static void vfio_ap_mdev_copy_masks(struct ap_matrix_mdev *matrix_mdev)
>> +{
>> +	int nbytes;
>> +	unsigned long *apm, *aqm, *adm;
>> +	struct kvm_s390_crypto_cb *crycb = matrix_mdev->kvm->arch.crypto.crycb;
>> +
>> +	switch (matrix_mdev->kvm->arch.crypto.crycbd & CRYCB_FORMAT_MASK) {
>> +	case CRYCB_FORMAT2:
>> +		apm = (unsigned long *)crycb->apcb1.apm;
>> +		aqm = (unsigned long *)crycb->apcb1.aqm;
>> +		adm = (unsigned long *)crycb->apcb1.adm;
>> +		break;
>> +	case CRYCB_FORMAT1:
>> +	case CRYCB_FORMAT0:
>> +	default:
> 
> That one looks a tad odd: the masking above should guarantee that we
> hit either the format 2, 1, or 0 cases, so the default case should
> never hit. Moreover, if the mask above will ever be changed, we don't
> know where we should look for the correct masks (what will a FORMAT<n>
> use: apcb1, apcb0, or something else?) Would it be better to moan in
> the default case and copy nothing?

It probably is a bit odd, but is not a problem now. If a new
format is added, one would hope the developer coding the change
would be smart enough to figure out what to do here.

> 
>> +		apm = (unsigned long *)crycb->apcb0.apm;
>> +		aqm = (unsigned long *)crycb->apcb0.aqm;
>> +		adm = (unsigned long *)crycb->apcb0.adm;
>> +		break;
>> +	}
>> +
>> +	nbytes = DIV_ROUND_UP(matrix_mdev->matrix.apm_max + 1, BITS_PER_BYTE);
>> +	memcpy(apm, matrix_mdev->matrix.apm, nbytes);
>> +	nbytes = DIV_ROUND_UP(matrix_mdev->matrix.aqm_max + 1, BITS_PER_BYTE);
>> +	memcpy(aqm, matrix_mdev->matrix.aqm, nbytes);
>> +	nbytes = DIV_ROUND_UP(matrix_mdev->matrix.adm_max + 1, BITS_PER_BYTE);
>> +	memcpy(adm, matrix_mdev->matrix.adm, nbytes);
>> +}
> 
> Anyway, that can be easily changed later on; in general,

true

> 
> Reviewed-by: Cornelia Huck <cohuck@...hat.com>
>