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

Heiko Carstens
2023-01-26T08:19:57Z

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@linux.ibm.com>
> ---
> 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).