On Wed, 2023-01-11 at 10:38 +0100, Janosch Frank wrote:
> 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@xxxxxxxxxxxxx>
> > ---
> > 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?
key is used with the skey flag, old_addr with the cmpxchg flag,
so yes only used with specific flags.
ar is used for logical accesses.
