Re: [PATCH 3/3] s390/vfio-ap: r/w lock for PQAP interception handler function pointer

Tony Krowiak
2021-06-15T18:55:48Z

On 6/15/21 4:55 AM, Christian Borntraeger wrote:
> On 10.06.21 00:46, Tony Krowiak wrote:
>> The function pointer to the interception handler for the PQAP
>> instruction
>> can get changed during the interception process. Let's add a
>> semaphore to struct kvm_s390_crypto to control read/write access to the
>> function pointer contained therein.
>>
>> The semaphore must be locked for write access by the vfio_ap device
>> driver
>> when notified that the KVM pointer has been set or cleared. It must be
>> locked for read access by the interception framework when the PQAP
>> instruction is intercepted.
>>
>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>
> Given that patch 2 is still  under discussion. Can this patch go
> without patch 2?

Here's what I think I'm going to do. Patches 1 and 3 are related to the
patch
I posted to resolve the FIXME in the vfio_ap_mdev_remove() callback in a
patch
posted by Jason Gunthorpe (Message ID:
<6-v1-d88406ed308e+418-vfio3_jgg@nvidia.com>).
Patch 2 in this series was precipitated by a comment Jason made that was
not directly related to that fix, so I will put a two patch series
with patch 1 and 3, then test them and post them here before proceeding
to resolving the issues in patch 2 which I will post separately.

>> ---
>>   arch/s390/include/asm/kvm_host.h      |  6 +++---
>>   arch/s390/kvm/kvm-s390.c              |  1 +
>>   arch/s390/kvm/priv.c                  |  6 +++---
>>   drivers/s390/crypto/vfio_ap_ops.c     | 14 ++++++++++----
>>   drivers/s390/crypto/vfio_ap_private.h |  2 +-
>>   5 files changed, 18 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h
>> b/arch/s390/include/asm/kvm_host.h
>> index 8925f3969478..58edaa3f9602 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -803,14 +803,14 @@ struct kvm_s390_cpu_model {
>>       unsigned short ibc;
>>   };
>>   -struct kvm_s390_module_hook {
>> +struct kvm_s390_crypto_hook {
>>       int (*hook)(struct kvm_vcpu *vcpu);
>> -    struct module *owner;
>>   };
>>     struct kvm_s390_crypto {
>>       struct kvm_s390_crypto_cb *crycb;
>> -    struct kvm_s390_module_hook *pqap_hook;
>> +    struct rw_semaphore pqap_hook_rwsem;
>> +    struct kvm_s390_crypto_hook *pqap_hook;
>>       __u32 crycbd;
>>       __u8 aes_kw;
>>       __u8 dea_kw;
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 1296fc10f80c..418d910df569 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -2606,6 +2606,7 @@ static void kvm_s390_crypto_init(struct kvm *kvm)
>>   {
>>       kvm->arch.crypto.crycb = &kvm->arch.sie_page2->crycb;
>>       kvm_s390_set_crycb_format(kvm);
>> +    init_rwsem(&kvm->arch.crypto.pqap_hook_rwsem);
>>         if (!test_kvm_facility(kvm, 76))
>>           return;
>> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
>> index 9928f785c677..bbbd84ffe239 100644
>> --- a/arch/s390/kvm/priv.c
>> +++ b/arch/s390/kvm/priv.c
>> @@ -657,15 +657,15 @@ static int handle_pqap(struct kvm_vcpu *vcpu)
>>        * Verify that the hook callback is registered, lock the owner
>>        * and call the hook.
>>        */
>> + down_read(&vcpu->kvm->arch.crypto.pqap_hook_rwsem);
>>       if (vcpu->kvm->arch.crypto.pqap_hook) {
>> -        if (!try_module_get(vcpu->kvm->arch.crypto.pqap_hook->owner))
>> -            return -EOPNOTSUPP;
>>           ret = vcpu->kvm->arch.crypto.pqap_hook->hook(vcpu);
>> - module_put(vcpu->kvm->arch.crypto.pqap_hook->owner);
>>           if (!ret && vcpu->run->s.regs.gprs[1] & 0x00ff0000)
>>               kvm_s390_set_psw_cc(vcpu, 3);
>> + up_read(&vcpu->kvm->arch.crypto.pqap_hook_rwsem);
>>           return ret;
>>       }
>> +    up_read(&vcpu->kvm->arch.crypto.pqap_hook_rwsem);
>>       /*
>>        * A vfio_driver must register a hook.
>>        * No hook means no driver to enable the SIE CRYCB and no queues.
>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c
>> b/drivers/s390/crypto/vfio_ap_ops.c
>> index d65a5728153b..2998c1b53ab9 100644
>> --- a/drivers/s390/crypto/vfio_ap_ops.c
>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>> @@ -342,7 +342,6 @@ static int vfio_ap_mdev_create(struct mdev_device
>> *mdev)
>>       init_rwsem(&matrix_mdev->rwsem);
>>       mdev_set_drvdata(mdev, matrix_mdev);
>>       matrix_mdev->pqap_hook.hook = handle_pqap;
>> -    matrix_mdev->pqap_hook.owner = THIS_MODULE;
>>         mutex_lock(&matrix_dev->lock);
>>       list_add(&matrix_mdev->node, &matrix_dev->mdev_list);
>> @@ -1063,7 +1062,6 @@ static int vfio_ap_mdev_set_kvm(struct
>> ap_matrix_mdev *matrix_mdev,
>>       down_write(&matrix_mdev->rwsem);
>>       matrix_mdev->kvm = kvm;
>>       kvm_get_kvm(kvm);
>> -    kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
>>       up_write(&matrix_mdev->rwsem);
>>         /*
>> @@ -1071,6 +1069,10 @@ static int vfio_ap_mdev_set_kvm(struct
>> ap_matrix_mdev *matrix_mdev,
>>        * masks for the KVM guest
>>        */
>>       if (kvm->arch.crypto.crycbd) {
>> + down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
>> +        kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
>> + up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
>> +
>>           down_read(&matrix_mdev->matrix.rwsem);
>>           kvm_arch_crypto_set_masks(kvm,
>>                         matrix_mdev->matrix.apm,
>> @@ -1122,11 +1124,15 @@ static int vfio_ap_mdev_iommu_notifier(struct
>> notifier_block *nb,
>>   static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
>>   {
>>       if (matrix_mdev->kvm) {
>> -        if (matrix_mdev->kvm->arch.crypto.crycbd)
>> +        if (matrix_mdev->kvm->arch.crypto.crycbd) {
>> + down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
>> +            matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>> + up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
>> +
>>               kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
>> +        }
>>             down_write(&matrix_mdev->rwsem);
>> -        matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
>>           vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
>>           kvm_put_kvm(matrix_mdev->kvm);
>>           matrix_mdev->kvm = NULL;
>> diff --git a/drivers/s390/crypto/vfio_ap_private.h
>> b/drivers/s390/crypto/vfio_ap_private.h
>> index a163ac04ff8a..3d6afd0faaaf 100644
>> --- a/drivers/s390/crypto/vfio_ap_private.h
>> +++ b/drivers/s390/crypto/vfio_ap_private.h
>> @@ -90,7 +90,7 @@ struct ap_matrix_mdev {
>>       struct notifier_block iommu_notifier;
>>       struct rw_semaphore rwsem;
>>       struct kvm *kvm;
>> -    struct kvm_s390_module_hook pqap_hook;
>> +    struct kvm_s390_crypto_hook pqap_hook;
>>       struct mdev_device *mdev;
>>   };
>>