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

[Jason Gunthorpe]

On Wed, Jun 09, 2021 at 06:46:34PM -0400, 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>
> ---
>  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(-)

This is alot better than the try_module_get!

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason