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Mon, 6 Feb 2023 16:46:10 +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 v7 13/14] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F_CMPXCHG Date: Mon, 6 Feb 2023 17:46:01 +0100 Message-Id: <20230206164602.138068-14-scgl@linux.ibm.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20230206164602.138068-1-scgl@linux.ibm.com> References: <20230206164602.138068-1-scgl@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 42RoMsJn4mnwGoDUIkTE0TzIbhfP90cL X-Proofpoint-ORIG-GUID: ZXysK4Z_W0wUXqwtqM4DngeODcjLv5y6 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.930,Hydra:6.0.562,FMLib:17.11.122.1 definitions=2023-02-06_07,2023-02-06_03,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 mlxscore=0 phishscore=0 spamscore=0 impostorscore=0 lowpriorityscore=0 adultscore=0 bulkscore=0 priorityscore=1501 mlxlogscore=950 malwarescore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2212070000 definitions=main-2302060144 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@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: Janosch Frank --- Documentation/virt/kvm/api.rst | 29 ++++++++++++++++++++++++++--- 1 file changed, 26 insertions(+), 3 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 0a67cb738013..d09d7223c2a6 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -3736,7 +3736,8 @@ 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 @@ -3754,6 +3755,8 @@ 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 */ @@ -3781,6 +3784,7 @@ Possible operations are: * ``KVM_S390_MEMOP_ABSOLUTE_WRITE`` * ``KVM_S390_MEMOP_SIDA_READ`` * ``KVM_S390_MEMOP_SIDA_WRITE`` + * ``KVM_S390_MEMOP_ABSOLUTE_CMPXCHG`` Logical read/write: ^^^^^^^^^^^^^^^^^^^ @@ -3829,7 +3833,7 @@ the checks required for storage key protection as one operation (as opposed to user space getting the storage keys, performing the checks, and accessing memory thereafter, which could lead to a delay between check and access). Absolute accesses are permitted for the VM ioctl if KVM_CAP_S390_MEM_OP_EXTENSION -is > 0. +has the KVM_S390_MEMOP_EXTENSION_CAP_BASE bit set. Currently absolute accesses are not permitted for VCPU ioctls. Absolute accesses are permitted for non-protected guests only. @@ -3837,7 +3841,26 @@ Supported flags: * ``KVM_S390_MEMOP_F_CHECK_ONLY`` * ``KVM_S390_MEMOP_F_SKEY_PROTECTION`` -The semantics of the flags are as for logical accesses. +The semantics of the flags common with logical accesses are as for logical +accesses. + +Absolute cmpxchg: +^^^^^^^^^^^^^^^^^ + +Perform cmpxchg on absolute guest memory. Intended for use with the +KVM_S390_MEMOP_F_SKEY_PROTECTION flag. +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, the value "old_addr" points to is replaced by the target value. +User space can tell if an exchange took place by checking if this replacement +occurred. The cmpxchg op is permitted for the VM ioctl if +KVM_CAP_S390_MEM_OP_EXTENSION has flag KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG set. + +Supported flags: + * ``KVM_S390_MEMOP_F_SKEY_PROTECTION`` SIDA read/write: ^^^^^^^^^^^^^^^^