From: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
To: Christian Borntraeger <borntraeger@linux.ibm.com>,
Janosch Frank <frankja@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: Janis Schoetterl-Glausch <scgl@linux.ibm.com>,
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>
Subject: [PATCH v6 13/14] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F_CMPXCHG
Date: Wed, 25 Jan 2023 22:26:07 +0100 [thread overview]
Message-ID: <20230125212608.1860251-14-scgl@linux.ibm.com> (raw)
In-Reply-To: <20230125212608.1860251-1-scgl@linux.ibm.com>
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 <scgl@linux.ibm.com>
---
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 9807b05a1b57..ce8a50d79232 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:
^^^^^^^^^^^^^^^^
--
2.34.1
next prev parent reply other threads:[~2023-01-25 21:26 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 21:25 [PATCH v6 00/14] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg Janis Schoetterl-Glausch
2023-01-25 21:25 ` [PATCH v6 01/14] KVM: s390: selftest: memop: Pass mop_desc via pointer Janis Schoetterl-Glausch
2023-01-26 11:51 ` Janosch Frank
2023-01-25 21:25 ` [PATCH v6 02/14] KVM: s390: selftest: memop: Replace macros by functions Janis Schoetterl-Glausch
2023-01-26 12:00 ` Janosch Frank
2023-01-25 21:25 ` [PATCH v6 03/14] KVM: s390: selftest: memop: Move testlist into main Janis Schoetterl-Glausch
2023-01-26 12:03 ` Janosch Frank
2023-01-25 21:25 ` [PATCH v6 04/14] KVM: s390: selftest: memop: Add bad address test Janis Schoetterl-Glausch
2023-01-26 15:23 ` Janosch Frank
2023-01-25 21:25 ` [PATCH v6 05/14] KVM: s390: selftest: memop: Fix typo Janis Schoetterl-Glausch
2023-01-25 21:26 ` [PATCH v6 06/14] KVM: s390: selftest: memop: Fix wrong address being used in test Janis Schoetterl-Glausch
2023-01-25 21:26 ` [PATCH v6 07/14] KVM: s390: selftest: memop: Fix integer literal Janis Schoetterl-Glausch
2023-01-26 6:38 ` Thomas Huth
2023-01-25 21:26 ` [PATCH v6 08/14] KVM: s390: Move common code of mem_op functions into functions Janis Schoetterl-Glausch
2023-01-26 6:48 ` Thomas Huth
2023-01-26 13:02 ` Janosch Frank
2023-01-26 16:47 ` Janis Schoetterl-Glausch
2023-01-26 17:01 ` Janis Schoetterl-Glausch
2023-01-25 21:26 ` [PATCH v6 09/14] KVM: s390: Dispatch to implementing function at top level of vm mem_op Janis Schoetterl-Glausch
2023-01-26 12:13 ` Thomas Huth
2023-01-25 21:26 ` [PATCH v6 10/14] KVM: s390: Refactor absolute vm mem_op function Janis Schoetterl-Glausch
2023-01-26 12:18 ` Thomas Huth
2023-01-26 13:02 ` Janosch Frank
2023-02-03 14:48 ` Janosch Frank
2023-02-03 15:32 ` Janis Schoetterl-Glausch
2023-01-25 21:26 ` [PATCH v6 11/14] KVM: s390: Refactor absolute vcpu " Janis Schoetterl-Glausch
2023-01-25 21:26 ` [PATCH v6 12/14] KVM: s390: Extend MEM_OP ioctl by storage key checked cmpxchg Janis Schoetterl-Glausch
2023-01-26 8:19 ` Heiko Carstens
2023-01-26 16:10 ` Janosch Frank
2023-01-27 18:15 ` Janis Schoetterl-Glausch
2023-01-28 9:29 ` kernel test robot
2023-01-28 14:38 ` kernel test robot
2023-01-28 14:38 ` kernel test robot
2023-01-25 21:26 ` Janis Schoetterl-Glausch [this message]
2023-01-25 21:26 ` [PATCH v6 14/14] KVM: s390: selftest: memop: Add cmpxchg tests Janis Schoetterl-Glausch
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