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Tue, 13 Dec 2022 16:54:13 +0000 (GMT) From: Janis Schoetterl-Glausch To: Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , Alexander Gordeev Cc: Janis Schoetterl-Glausch , David Hildenbrand , Jonathan Corbet , 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 , Shuah Khan , Sven Schnelle Subject: [PATCH v4 2/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F_CMPXCHG Date: Tue, 13 Dec 2022 17:53:58 +0100 Message-Id: <20221213165405.2953539-3-scgl@linux.ibm.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20221213165405.2953539-1-scgl@linux.ibm.com> References: <20221213165405.2953539-1-scgl@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: y9rxpg2hT1ShmnreNGnXJrQYIpgnpjfH X-Proofpoint-ORIG-GUID: cdDGzcxPwSWI3eZo6yhfs8WiqVY4i8D5 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.923,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-12-13_03,2022-12-13_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 impostorscore=0 suspectscore=0 adultscore=0 bulkscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 mlxlogscore=681 mlxscore=0 spamscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2210170000 definitions=main-2212130147 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Describe the semantics of the new KVM_S390_MEMOP_F_CMPXCHG flag for absolute vm write memops which allows user space to perform (storage key checked) cmpxchg operations on guest memory. Signed-off-by: Janis Schoetterl-Glausch Reviewed-by: Claudio Imbrenda --- Documentation/virt/kvm/api.rst | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index eee9f857a986..98f5a35088b8 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -3753,7 +3753,8 @@ The fields in each entry are defined as follows: :Parameters: struct kvm_s390_mem_op (in) :Returns: = 0 on success, < 0 on generic error (e.g. -EFAULT or -ENOMEM), - > 0 if an exception occurred while walking the page tables + 16 bit program exception code if the access causes such an exception + other code > 0xffff with special meaning Read or write data from/to the VM's memory. The KVM_CAP_S390_MEM_OP_EXTENSION capability specifies what functionality is @@ -3771,6 +3772,8 @@ Parameters are specified via the following structure:: 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 */ }; __u32 sida_offset; /* offset into the sida */ __u8 reserved[32]; /* ignored */ @@ -3853,8 +3856,21 @@ Absolute accesses are permitted for non-protected guests only. Supported flags: * ``KVM_S390_MEMOP_F_CHECK_ONLY`` * ``KVM_S390_MEMOP_F_SKEY_PROTECTION`` + * ``KVM_S390_MEMOP_F_CMPXCHG`` + +The semantics of the flags common with logical accesses are as for logical +accesses. + +For write accesses, the KVM_S390_MEMOP_F_CMPXCHG flag is supported if +KVM_CAP_S390_MEM_OP_EXTENSION has flag KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG set. +In this case, instead of doing an unconditional write, the access occurs +only if the target location contains the value pointed to by "old_addr". +This is performed as an atomic cmpxchg with the length specified by the "size" +parameter. "size" must be a power of two up to and including 16. +If the exchange did not take place because the target value doesn't match the +old value, KVM_S390_MEMOP_R_NO_XCHG is returned. +In this case the value "old_addr" points to is replaced by the target value. -The semantics of the flags are as for logical accesses. SIDA read/write: ^^^^^^^^^^^^^^^^