Re: [PATCH v6 12/14] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg

[Heiko Carstens]

On Wed, Jan 25, 2023 at 10:26:06PM +0100, Janis Schoetterl-Glausch wrote:
> User space can use the MEM_OP ioctl to make storage key checked reads
> and writes to the guest, however, it has no way of performing atomic,
> key checked, accesses to the guest.
> Extend the MEM_OP ioctl in order to allow for this, by adding a cmpxchg
> op. For now, support this op for absolute accesses only.
> 
> This op can be use, for example, to set the device-state-change
> indicator and the adapter-local-summary indicator atomically.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@xxxxxxxxxxxxx>
> ---
>  include/uapi/linux/kvm.h |   8 +++
>  arch/s390/kvm/gaccess.h  |   3 ++
>  arch/s390/kvm/gaccess.c  | 103 +++++++++++++++++++++++++++++++++++++++
>  arch/s390/kvm/kvm-s390.c |  56 ++++++++++++++++++++-
>  4 files changed, 169 insertions(+), 1 deletion(-)
...
> +		ret = cmpxchg_user_key((u8 *)hva, &old, *old_addr, new, access_key);

FWIW, this and the three others need a __user annotation:

		ret = cmpxchg_user_key((u8 __user *)hva, &old, *old_addr, new, access_key);

Otherwise you end up with sparse warnings (compile with C=1).