Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <839f7ee6c273f8542f06d3330622e545b86b8abc.camel@linux.ibm.com>
Subject: Re: [PATCH v5 01/10] KVM: s390: Extend MEM_OP ioctl by storage key
 checked cmpxchg
From:   Janis Schoetterl-Glausch <scgl@linux.ibm.com>
To:     Janosch Frank <frankja@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>, kvm@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-s390@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Shuah Khan <shuah@kernel.org>,
        Sven Schnelle <svens@linux.ibm.com>
Date:   Wed, 11 Jan 2023 16:29:51 +0100
In-Reply-To: <10ba824d-6174-2fc4-b58b-a914cc5524be@linux.ibm.com>
References: <20230110202632.2533978-1-scgl@linux.ibm.com>
         <20230110202632.2533978-2-scgl@linux.ibm.com>
         <10ba824d-6174-2fc4-b58b-a914cc5524be@linux.ibm.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.46.2 (3.46.2-1.fc37) 
MIME-Version: 1.0
Precedence: bulk

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.
> >=20
> > This mode can be use, for example, to set the device-state-change
> > indicator and the adapter-local-summary indicator atomically.
> >=20
> > 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(-)
> >=20
> > 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 */
>=20
> These 3 are only used for flag values >=3D4, 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.