Re: [PATCH v3 1/9] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg

Janis Schoetterl-Glausch
2022-11-21T17:42:20Z

On Fri, 2022-11-18 at 11:12 +0100, Heiko Carstens wrote:
> On Thu, Nov 17, 2022 at 11:17:50PM +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
> > 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 | 5 ++
> > arch/s390/kvm/gaccess.h | 3 ++
> > arch/s390/kvm/gaccess.c | 101 +++++++++++++++++++++++++++++++++++++++
> > arch/s390/kvm/kvm-s390.c | 35 +++++++++++++-
> > 4 files changed, 142 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index 0d5d4419139a..1f36be5493e6 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -588,6 +588,8 @@ 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_p; /* ignored if flag unset */
>
> Just one comment: the suffix "_p" for pointer is quite unusual within
> the kernel. This also would be the first of its kind within kvm.h.
> Usually there is either no suffix or "_addr".
> So for consistency reasons I would suggest to change this to one of
> the common variants.
>
Thanks, good point. …