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).