Re: [PATCH v5 01/10] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg

[Janosch Frank <frankja@linux.ibm.com>]

On 1/10/23 21:26, 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
> mode. For now, support this mode for absolute accesses only.
> 
> This mode 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@linux.ibm.com>
> ---
>   include/uapi/linux/kvm.h |   7 +++
>   arch/s390/kvm/gaccess.h  |   3 ++
>   arch/s390/kvm/gaccess.c  | 102 +++++++++++++++++++++++++++++++++++++++
>   arch/s390/kvm/kvm-s390.c |  41 +++++++++++++++-
>   4 files changed, 151 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 55155e262646..452f43c1cc34 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -583,6 +583,8 @@ struct kvm_s390_mem_op {
>   		struct {
>   			__u8 ar;	/* the access register number */
>   			__u8 key;	/* access key, ignored if flag unset */
> +			__u8 pad1[6];	/* ignored */
> +			__u64 old_addr;	/* ignored if flag unset */

These 3 are only used for flag values >=4, no?
They aren't used for all flag values but for specific ones, right?