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Subject: Re: [PATCH v12 12/17] s390/vfio-ap: allow hot plug/unplug of AP
 resources using mdev device
To:     Halil Pasic <pasic@linux.ibm.com>
Cc:     linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, freude@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, frankja@linux.ibm.com, david@redhat.com,
        hca@linux.ibm.com, gor@linux.ibm.com
References: <20201124214016.3013-1-akrowiak@linux.ibm.com>
 <20201124214016.3013-13-akrowiak@linux.ibm.com>
 <20201129025250.16eb8355.pasic@linux.ibm.com>
From:   Tony Krowiak <akrowiak@linux.ibm.com>
Message-ID: <103cbe02-2093-c950-8d65-d3dc385942ce@linux.ibm.com>
Date:   Mon, 30 Nov 2020 14:36:10 -0500
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On 11/28/20 8:52 PM, Halil Pasic wrote:
> On Tue, 24 Nov 2020 16:40:11 -0500
> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
>
>> Let's hot plug/unplug adapters, domains and control domains assigned to or
>> unassigned from an AP matrix mdev device while it is in use by a guest per
>> the following rules:
>>
>> * Assign an adapter to mdev's matrix:
>>
>>    The adapter will be hot plugged into the guest under the following
>>    conditions:
>>    1. The adapter is not yet assigned to the guest's matrix
>>    2. At least one domain is assigned to the guest's matrix
>>    3. Each APQN derived from the APID of the newly assigned adapter and
>>       the APQIs of the domains already assigned to the guest's
>>       matrix references a queue device bound to the vfio_ap device driver.
>>
>>    The adapter and each domain assigned to the mdev's matrix will be hot
>>    plugged into the guest under the following conditions:
>>    1. The adapter is not yet assigned to the guest's matrix
>>    2. No domains are assigned to the guest's matrix
>>    3  At least one domain is assigned to the mdev's matrix
>>    4. Each APQN derived from the APID of the newly assigned adapter and
>>       the APQIs of the domains assigned to the mdev's matrix references a
>>       queue device bound to the vfio_ap device driver.
>>
>> * Unassign an adapter from mdev's matrix:
>>
>>    The adapter will be hot unplugged from the KVM guest if it is
>>    assigned to the guest's matrix.
>>
>> * Assign a domain to mdev's matrix:
>>
>>    The domain will be hot plugged into the guest under the following
>>    conditions:
>>    1. The domain is not yet assigned to the guest's matrix
>>    2. At least one adapter is assigned to the guest's matrix
>>    3. Each APQN derived from the APQI of the newly assigned domain and
>>       the APIDs of the adapters already assigned to the guest's
>>       matrix references a queue device bound to the vfio_ap device driver.
>>
>>    The domain and each adapter assigned to the mdev's matrix will be hot
>>    plugged into the guest under the following conditions:
>>    1. The domain is not yet assigned to the guest's matrix
>>    2. No adapters are assigned to the guest's matrix
>>    3  At least one adapter is assigned to the mdev's matrix
>>    4. Each APQN derived from the APQI of the newly assigned domain and
>>       the APIDs of the adapters assigned to the mdev's matrix references a
>>       queue device bound to the vfio_ap device driver.
>>
>> * Unassign adapter from mdev's matrix:
>>
>>    The domain will be hot unplugged from the KVM guest if it is
>>    assigned to the guest's matrix.
>>
>> * Assign a control domain:
>>
>>    The control domain will be hot plugged into the KVM guest if it is not
>>    assigned to the guest's APCB. The AP architecture ensures a guest will
>>    only get access to the control domain if it is in the host's AP
>>    configuration, so there is no risk in hot plugging it; however, it will
>>    become automatically available to the guest when it is added to the host
>>    configuration.
>>
>> * Unassign a control domain:
>>
>>    The control domain will be hot unplugged from the KVM guest if it is
>>    assigned to the guest's APCB.
> This is where things start getting tricky. E.g. do we need to revise
> filtering after an unassign? (For example an assign_adapter X didn't
> change the shadow, because queue XY was missing, but now we unplug domain
> Y. Should the adapter X pop up? I guess it should.)

I suppose that makes sense at the expense of making the code
more complex. It is essentially what we had in the prior version
which used the same filtering code for assignment as well as
host AP configuration changes.

>
>
>> Note: Now that hot plug/unplug is implemented, there is the possibility
>>        that an assignment/unassignment of an adapter, domain or control
>>        domain could be initiated while the guest is starting, so the
>>        matrix device lock will be taken for the group notification callback
>>        that initializes the guest's APCB when the KVM pointer is made
>>        available to the vfio_ap device driver.
>>
>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>> ---
>>   drivers/s390/crypto/vfio_ap_ops.c | 190 +++++++++++++++++++++++++-----
>>   1 file changed, 159 insertions(+), 31 deletions(-)
>>
>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
>> index 586ec5776693..4f96b7861607 100644
>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>> @@ -631,6 +631,60 @@ static void vfio_ap_mdev_manage_qlinks(struct ap_matrix_mdev *matrix_mdev,
>>   	}
>>   }
>>   
>> +static bool vfio_ap_assign_apid_to_apcb(struct ap_matrix_mdev *matrix_mdev,
>> +					unsigned long apid)
>> +{
>> +	unsigned long apqi, apqn;
>> +	unsigned long *aqm = matrix_mdev->shadow_apcb.aqm;
>> +
>> +	/*
>> +	 * If the APID is already assigned to the guest's shadow APCB, there is
>> +	 * no need to assign it.
>> +	 */
>> +	if (test_bit_inv(apid, matrix_mdev->shadow_apcb.apm))
>> +		return false;
>> +
>> +	/*
>> +	 * If no domains have yet been assigned to the shadow APCB and one or
>> +	 * more domains have been assigned to the matrix mdev, then use
>> +	 * the domains assigned to the matrix mdev; otherwise, there is nothing
>> +	 * to assign to the shadow APCB.
>> +	 */
>> +	if (bitmap_empty(matrix_mdev->shadow_apcb.aqm, AP_DOMAINS)) {
>> +		if (bitmap_empty(matrix_mdev->matrix.aqm, AP_DOMAINS))
>> +			return false;
>> +
>> +		aqm = matrix_mdev->matrix.aqm;
>> +	}
>> +
>> +	/* Make sure all APQNs are bound to the vfio_ap driver */
>> +	for_each_set_bit_inv(apqi, aqm, AP_DOMAINS) {
>> +		apqn = AP_MKQID(apid, apqi);
>> +
>> +		if (vfio_ap_mdev_get_queue(matrix_mdev, apqn) == NULL)
>> +			return false;
>> +	}
>> +
>> +	set_bit_inv(apid, matrix_mdev->shadow_apcb.apm);
>> +
>> +	/*
>> +	 * If we verified APQNs using the domains assigned to the matrix mdev,
>> +	 * then copy the APQIs of those domains into the guest's APCB
>> +	 */
>> +	if (bitmap_empty(matrix_mdev->shadow_apcb.aqm, AP_DOMAINS))
>> +		bitmap_copy(matrix_mdev->shadow_apcb.aqm,
>> +			    matrix_mdev->matrix.aqm, AP_DOMAINS);
>> +
>> +	return true;
>> +}
> What is the rationale behind the shadow aqm empty special handling?

The rationale was to avoid taking the VCPUs
out of SIE in order to make an update to the guest's APCB
unnecessarily. For example, suppose the guest is started
without access to any APQNs (i.e., all matrix and shadow_apcb
masks are zeros). Now suppose the administrator proceeds to
start assigning AP resources to the mdev. Let's say he starts
by assigning adapters 1 through 100. The code below will return
true indicating the shadow_apcb was updated. Consequently,
the calling code will commit the changes to the guest's
APCB. The problem there is that in order to update the guest's
VCPUs, they will have to be taken out of SIE, yet the guest will
not get access to the adapter since no domains have yet been
assigned to the APCB. Doing this 100 times - once for each
adapter 1-100 - is probably a bad idea.

>   I.e.
> why not simply:
>
>
> static bool vfio_ap_assign_apid_to_apcb(struct ap_matrix_mdev *matrix_mdev,
>                                          unsigned long apid)
> {
>          unsigned long apqi, apqn;
>          unsigned long *aqm = matrix_mdev->shadow_apcb.aqm;
>                                                                                  
>          /*
>           * If the APID is already assigned to the guest's shadow APCB, there is
>           * no need to assign it.
>           */
>          if (test_bit_inv(apid, matrix_mdev->shadow_apcb.apm))
>                  return false;
>                                                                                  
>          /* Make sure all APQNs are bound to the vfio_ap driver */
>          for_each_set_bit_inv(apqi, aqm, AP_DOMAINS) {
>                  apqn = AP_MKQID(apid, apqi);
>                                                                                  
>                  if (vfio_ap_mdev_get_queue(matrix_mdev, apqn) == NULL)
>                          return false;
>          }
>                                                                                  
>          set_bit_inv(apid, matrix_mdev->shadow_apcb.apm);
>                                                                                  
>          return true;
> }
>
> Please answer the questions I've asked, and note that I will have to
> return to this patch, later.
>
> Regards,
> Halil
>
>> +
>> +static void vfio_ap_mdev_hot_plug_adapter(struct ap_matrix_mdev *matrix_mdev,
>> +					  unsigned long apid)
>> +{
>> +	if (vfio_ap_assign_apid_to_apcb(matrix_mdev, apid))
>> +		vfio_ap_mdev_commit_shadow_apcb(matrix_mdev);
>> +}
>> +
>>   /**
>>    * assign_adapter_store
>>    *
>> @@ -673,10 +727,6 @@ static ssize_t assign_adapter_store(struct device *dev,
>>   	struct mdev_device *mdev = mdev_from_dev(dev);
>>   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>>   
>> -	/* If the guest is running, disallow assignment of adapter */
>> -	if (matrix_mdev->kvm)
>> -		return -EBUSY;
>> -
>>   	ret = kstrtoul(buf, 0, &apid);
>>   	if (ret)
>>   		return ret;
>> @@ -698,12 +748,22 @@ static ssize_t assign_adapter_store(struct device *dev,
>>   	}
>>   	set_bit_inv(apid, matrix_mdev->matrix.apm);
>>   	vfio_ap_mdev_manage_qlinks(matrix_mdev, LINK_APID, apid);
>> +	vfio_ap_mdev_hot_plug_adapter(matrix_mdev, apid);
>>   	mutex_unlock(&matrix_dev->lock);
>>   
>>   	return count;
>>   }
>>   static DEVICE_ATTR_WO(assign_adapter);
>>   
>> +static void vfio_ap_mdev_hot_unplug_adapter(struct ap_matrix_mdev *matrix_mdev,
>> +					    unsigned long apid)
>> +{
>> +	if (test_bit_inv(apid, matrix_mdev->shadow_apcb.apm)) {
>> +		clear_bit_inv(apid, matrix_mdev->shadow_apcb.apm);
>> +		vfio_ap_mdev_commit_shadow_apcb(matrix_mdev);
>> +	}
>> +}
>> +
>>   /**
>>    * unassign_adapter_store
>>    *
>> @@ -730,10 +790,6 @@ static ssize_t unassign_adapter_store(struct device *dev,
>>   	struct mdev_device *mdev = mdev_from_dev(dev);
>>   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>>   
>> -	/* If the guest is running, disallow un-assignment of adapter */
>> -	if (matrix_mdev->kvm)
>> -		return -EBUSY;
>> -
>>   	ret = kstrtoul(buf, 0, &apid);
>>   	if (ret)
>>   		return ret;
>> @@ -744,12 +800,67 @@ static ssize_t unassign_adapter_store(struct device *dev,
>>   	mutex_lock(&matrix_dev->lock);
>>   	clear_bit_inv((unsigned long)apid, matrix_mdev->matrix.apm);
>>   	vfio_ap_mdev_manage_qlinks(matrix_mdev, UNLINK_APID, apid);
>> +	vfio_ap_mdev_hot_unplug_adapter(matrix_mdev, apid);
>>   	mutex_unlock(&matrix_dev->lock);
>>   
>>   	return count;
>>   }
>>   static DEVICE_ATTR_WO(unassign_adapter);
>>   
>> +static bool vfio_ap_assign_apqi_to_apcb(struct ap_matrix_mdev *matrix_mdev,
>> +					unsigned long apqi)
>> +{
>> +	unsigned long apid, apqn;
>> +	unsigned long *apm = matrix_mdev->shadow_apcb.apm;
>> +
>> +	/*
>> +	 * If the APQI is already assigned to the guest's shadow APCB, there is
>> +	 * no need to assign it.
>> +	 */
>> +	if (test_bit_inv(apqi, matrix_mdev->shadow_apcb.aqm))
>> +		return false;
>> +
>> +	/*
>> +	 * If no adapters have yet been assigned to the shadow APCB and one or
>> +	 * more adapters have been assigned to the matrix mdev, then use
>> +	 * the adapters assigned to the matrix mdev; otherwise, there is nothing
>> +	 * to assign to the shadow APCB.
>> +	 */
>> +	if (bitmap_empty(matrix_mdev->shadow_apcb.apm, AP_DEVICES)) {
>> +		if (bitmap_empty(matrix_mdev->matrix.apm, AP_DEVICES))
>> +			return false;
>> +
>> +		apm = matrix_mdev->matrix.apm;
>> +	}
>> +
>> +	/* Make sure all APQNs are bound to the vfio_ap driver */
>> +	for_each_set_bit_inv(apid, apm, AP_DEVICES) {
>> +		apqn = AP_MKQID(apid, apqi);
>> +
>> +		if (vfio_ap_mdev_get_queue(matrix_mdev, apqn) == NULL)
>> +			return false;
>> +	}
>> +
>> +	set_bit_inv(apqi, matrix_mdev->shadow_apcb.aqm);
>> +
>> +	/*
>> +	 * If we verified APQNs using the adapters assigned to the matrix mdev,
>> +	 * then copy the APIDs of those adapters into the guest's APCB
>> +	 */
>> +	if (bitmap_empty(matrix_mdev->shadow_apcb.apm, AP_DEVICES))
>> +		bitmap_copy(matrix_mdev->shadow_apcb.apm,
>> +			    matrix_mdev->matrix.apm, AP_DEVICES);
>> +
>> +	return true;
>> +}
>> +
>> +static void vfio_ap_mdev_hot_plug_domain(struct ap_matrix_mdev *matrix_mdev,
>> +					 unsigned long apqi)
>> +{
>> +	if (vfio_ap_assign_apqi_to_apcb(matrix_mdev, apqi))
>> +		vfio_ap_mdev_commit_shadow_apcb(matrix_mdev);
>> +}
>> +
>>   /**
>>    * assign_domain_store
>>    *
>> @@ -793,10 +904,6 @@ static ssize_t assign_domain_store(struct device *dev,
>>   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>>   	unsigned long max_apqi = matrix_mdev->matrix.aqm_max;
>>   
>> -	/* If the guest is running, disallow assignment of domain */
>> -	if (matrix_mdev->kvm)
>> -		return -EBUSY;
>> -
>>   	ret = kstrtoul(buf, 0, &apqi);
>>   	if (ret)
>>   		return ret;
>> @@ -817,12 +924,21 @@ static ssize_t assign_domain_store(struct device *dev,
>>   	}
>>   	set_bit_inv(apqi, matrix_mdev->matrix.aqm);
>>   	vfio_ap_mdev_manage_qlinks(matrix_mdev, LINK_APQI, apqi);
>> +	vfio_ap_mdev_hot_plug_domain(matrix_mdev, apqi);
>>   	mutex_unlock(&matrix_dev->lock);
>>   
>>   	return count;
>>   }
>>   static DEVICE_ATTR_WO(assign_domain);
>>   
>> +static void vfio_ap_mdev_hot_unplug_domain(struct ap_matrix_mdev *matrix_mdev,
>> +					   unsigned long apqi)
>> +{
>> +	if (test_bit_inv(apqi, matrix_mdev->shadow_apcb.aqm)) {
>> +		clear_bit_inv(apqi, matrix_mdev->shadow_apcb.aqm);
>> +		vfio_ap_mdev_commit_shadow_apcb(matrix_mdev);
>> +	}
>> +}
>>   
>>   /**
>>    * unassign_domain_store
>> @@ -850,10 +966,6 @@ static ssize_t unassign_domain_store(struct device *dev,
>>   	struct mdev_device *mdev = mdev_from_dev(dev);
>>   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>>   
>> -	/* If the guest is running, disallow un-assignment of domain */
>> -	if (matrix_mdev->kvm)
>> -		return -EBUSY;
>> -
>>   	ret = kstrtoul(buf, 0, &apqi);
>>   	if (ret)
>>   		return ret;
>> @@ -864,12 +976,22 @@ static ssize_t unassign_domain_store(struct device *dev,
>>   	mutex_lock(&matrix_dev->lock);
>>   	clear_bit_inv((unsigned long)apqi, matrix_mdev->matrix.aqm);
>>   	vfio_ap_mdev_manage_qlinks(matrix_mdev, UNLINK_APQI, apqi);
>> +	vfio_ap_mdev_hot_unplug_domain(matrix_mdev, apqi);
>>   	mutex_unlock(&matrix_dev->lock);
>>   
>>   	return count;
>>   }
>>   static DEVICE_ATTR_WO(unassign_domain);
>>   
>> +static void vfio_ap_mdev_hot_plug_ctl_domain(struct ap_matrix_mdev *matrix_mdev,
>> +					     unsigned long domid)
>> +{
>> +	if (!test_bit_inv(domid, matrix_mdev->shadow_apcb.adm)) {
>> +		set_bit_inv(domid, matrix_mdev->shadow_apcb.adm);
>> +		vfio_ap_mdev_commit_shadow_apcb(matrix_mdev);
>> +	}
>> +}
>> +
>>   /**
>>    * assign_control_domain_store
>>    *
>> @@ -895,10 +1017,6 @@ static ssize_t assign_control_domain_store(struct device *dev,
>>   	struct mdev_device *mdev = mdev_from_dev(dev);
>>   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>>   
>> -	/* If the guest is running, disallow assignment of control domain */
>> -	if (matrix_mdev->kvm)
>> -		return -EBUSY;
>> -
>>   	ret = kstrtoul(buf, 0, &id);
>>   	if (ret)
>>   		return ret;
>> @@ -914,12 +1032,23 @@ static ssize_t assign_control_domain_store(struct device *dev,
>>   	if (!mutex_trylock(&matrix_dev->lock))
>>   		return -EBUSY;
>>   	set_bit_inv(id, matrix_mdev->matrix.adm);
>> +	vfio_ap_mdev_hot_plug_ctl_domain(matrix_mdev, id);
>>   	mutex_unlock(&matrix_dev->lock);
>>   
>>   	return count;
>>   }
>>   static DEVICE_ATTR_WO(assign_control_domain);
>>   
>> +static void
>> +vfio_ap_mdev_hot_unplug_ctl_domain(struct ap_matrix_mdev *matrix_mdev,
>> +				   unsigned long domid)
>> +{
>> +	if (test_bit_inv(domid, matrix_mdev->shadow_apcb.adm)) {
>> +		clear_bit_inv(domid, matrix_mdev->shadow_apcb.adm);
>> +		vfio_ap_mdev_commit_shadow_apcb(matrix_mdev);
>> +	}
>> +}
>> +
>>   /**
>>    * unassign_control_domain_store
>>    *
>> @@ -946,10 +1075,6 @@ static ssize_t unassign_control_domain_store(struct device *dev,
>>   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>>   	unsigned long max_domid =  matrix_mdev->matrix.adm_max;
>>   
>> -	/* If the guest is running, disallow un-assignment of control domain */
>> -	if (matrix_mdev->kvm)
>> -		return -EBUSY;
>> -
>>   	ret = kstrtoul(buf, 0, &domid);
>>   	if (ret)
>>   		return ret;
>> @@ -958,6 +1083,7 @@ static ssize_t unassign_control_domain_store(struct device *dev,
>>   
>>   	mutex_lock(&matrix_dev->lock);
>>   	clear_bit_inv(domid, matrix_mdev->matrix.adm);
>> +	vfio_ap_mdev_hot_unplug_ctl_domain(matrix_mdev, domid);
>>   	mutex_unlock(&matrix_dev->lock);
>>   
>>   	return count;
>> @@ -1099,8 +1225,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>>   {
>>   	struct ap_matrix_mdev *m;
>>   
>> -	mutex_lock(&matrix_dev->lock);
>> -
>>   	list_for_each_entry(m, &matrix_dev->mdev_list, node) {
>>   		if ((m != matrix_mdev) && (m->kvm == kvm)) {
>>   			mutex_unlock(&matrix_dev->lock);
>> @@ -1111,7 +1235,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>>   	matrix_mdev->kvm = kvm;
>>   	kvm_get_kvm(kvm);
>>   	kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
>> -	mutex_unlock(&matrix_dev->lock);
>>   
>>   	return 0;
>>   }
>> @@ -1148,7 +1271,7 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
>>   static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
>>   				       unsigned long action, void *data)
>>   {
>> -	int ret;
>> +	int ret = NOTIFY_DONE;
>>   	struct ap_matrix_mdev *matrix_mdev;
>>   
>>   	if (action != VFIO_GROUP_NOTIFY_SET_KVM)
>> @@ -1156,23 +1279,28 @@ static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
>>   
>>   	matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
>>   
>> +	mutex_lock(&matrix_dev->lock);
>> +
>>   	if (!data) {
>>   		if (matrix_mdev->kvm)
>>   			kvm_put_kvm(matrix_mdev->kvm);
>>   
>>   		matrix_mdev->kvm = NULL;
>>   
>> -		return NOTIFY_OK;
>> +		ret = NOTIFY_OK;
>> +		goto done;
>>   	}
>>   
>>   	ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
>>   	if (ret)
>> -		return NOTIFY_DONE;
>> +		goto done;
>>   
>>   	vfio_ap_mdev_init_apcb(matrix_mdev);
>>   	vfio_ap_mdev_commit_shadow_apcb(matrix_mdev);
>>   
>> -	return NOTIFY_OK;
>> +done:
>> +	mutex_unlock(&matrix_dev->lock);
>> +	return ret;
>>   }
>>   
>>   static int vfio_ap_mdev_reset_queue(unsigned int apid, unsigned int apqi,