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

[Tony Krowiak <akrowiak@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxx>).
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;
> >   };