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SubjectRe: [PATCH 1/2] s390/vfio-ap: r/w lock for PQAP interception handler function pointer
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On 19.07.21 21:35, 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>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
> arch/s390/include/asm/kvm_host.h | 8 +++-----
> arch/s390/kvm/kvm-s390.c | 1 +
> arch/s390/kvm/priv.c | 10 ++++++----
> drivers/s390/crypto/vfio_ap_ops.c | 23 +++++++++++++++++------
> drivers/s390/crypto/vfio_ap_private.h | 2 +-
> 5 files changed, 28 insertions(+), 16 deletions(-)
>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 9b4473f76e56..f18849d259e6 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -798,14 +798,12 @@ struct kvm_s390_cpu_model {
> unsigned short ibc;
> };
>
> -struct kvm_s390_module_hook {
> - int (*hook)(struct kvm_vcpu *vcpu);
> - struct module *owner;
> -};
> +typedef int (*crypto_hook)(struct kvm_vcpu *vcpu);
>
> struct kvm_s390_crypto {
> struct kvm_s390_crypto_cb *crycb;
> - struct kvm_s390_module_hook *pqap_hook;
> + struct rw_semaphore pqap_hook_rwsem;
> + 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 b655a7d82bf0..a08f242a9f27 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2630,6 +2630,7 @@ 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..6bed9406c1f3 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -610,6 +610,7 @@ static int handle_io_inst(struct kvm_vcpu *vcpu)
> static int handle_pqap(struct kvm_vcpu *vcpu)
> {
> struct ap_queue_status status = {};
> + crypto_hook pqap_hook;
> unsigned long reg0;
> int ret;
> uint8_t fc;
> @@ -657,15 +658,16 @@ 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);
> + pqap_hook = *vcpu->kvm->arch.crypto.pqap_hook;

Dont we have to check for NULL here? If not can you add a comment why?

Otherwise this looks good.


> + ret = pqap_hook(vcpu);
[...]

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