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Thu, 13 Nov 2025 14:33:15 +0000 (GMT) From: Janosch Frank To: kvm@vger.kernel.org Cc: linux-s390@vger.kernel.org, imbrenda@linux.ibm.com, borntraeger@linux.ibm.com, thuth@redhat.com Subject: [PATCH v2] KVM: s390: Add capability that forwards operation exceptions Date: Thu, 13 Nov 2025 14:32:22 +0000 Message-ID: <20251113143310.4187-1-frankja@linux.ibm.com> X-Mailer: git-send-email 2.48.1 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTA4MDAyMiBTYWx0ZWRfXwg8wQ0ISjlWU kOL1KadZdOxf0/44Pk/1bRTeSnVaPlfbj1dBVc5sakkGLz0VPwGCiCz/o1gZg9m7NJYUTd1kAhh fqZDUb30OpBxgGeHdMwWZPWCZEbck2tNuwm3Q/CCGcN6xRALTRbhqR1/ZTe8ldeBZrrXtOiESAy 5rpjNpgs9F+cn0TnC4MwlecBCSaL3x23GG6A3cL6msZw1Q2bdzfIaAGpR9qGgP7g/XbrB6/LkkK eISfdJDL36WE2PWAMLBW1BXiKwp6PcE4HxO/oOvz/EIsfR7H+apB8zTCFxIkvBzBi4eWJ0xtFni GssBO6KUKxBbhwfo/pP6yjrQE1D0UIN096uvGzNxZTVJyqSl6nVFrC6yKtPvaRep4bY68NW4+Sy d5sqQW65/OlSpf+5OSoOJ1bVUI8eSg== X-Authority-Analysis: v=2.4 cv=ZK3aWH7b c=1 sm=1 tr=0 ts=6915ec30 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=2J_RzahkHEl8vmpqG00A:9 X-Proofpoint-ORIG-GUID: l1lgQes7MlUj3m4YL0jW-kSxV2P6bsWr X-Proofpoint-GUID: l1lgQes7MlUj3m4YL0jW-kSxV2P6bsWr X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-13_02,2025-11-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 lowpriorityscore=0 priorityscore=1501 suspectscore=0 phishscore=0 impostorscore=0 spamscore=0 bulkscore=0 adultscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511080022 Setting KVM_CAP_S390_USER_OPEREXEC will forward all operation exceptions to user space. This also includes the 0x0000 instructions managed by KVM_CAP_S390_USER_INSTR0. It's helpful if user space wants to emulate instructions which do not (yet) have an opcode. While we're at it refine the documentation for KVM_CAP_S390_USER_INSTR0. Signed-off-by: Janosch Frank Reviewed-by: Claudio Imbrenda Acked-by: Christian Borntraeger --- Reworded api documentation as per Thomas' request. --- Documentation/virt/kvm/api.rst | 17 ++- arch/s390/include/asm/kvm_host.h | 1 + arch/s390/kvm/intercept.c | 3 + arch/s390/kvm/kvm-s390.c | 7 + include/uapi/linux/kvm.h | 1 + tools/testing/selftests/kvm/Makefile.kvm | 1 + .../selftests/kvm/s390/user_operexec.c | 140 ++++++++++++++++++ 7 files changed, 169 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/kvm/s390/user_operexec.c diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 72b2fae99a83..9d2b1c08d321 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7820,7 +7820,7 @@ where 0xff represents CPUs 0-7 in cluster 0. :Architectures: s390 :Parameters: none -With this capability enabled, all illegal instructions 0x0000 (2 bytes) will +With this capability enabled, the illegal instruction 0x0000 (2 bytes) will be intercepted and forwarded to user space. User space can use this mechanism e.g. to realize 2-byte software breakpoints. The kernel will not inject an operating exception for these instructions, user space has @@ -8703,6 +8703,21 @@ This capability indicate to the userspace whether a PFNMAP memory region can be safely mapped as cacheable. This relies on the presence of force write back (FWB) feature support on the hardware. +7.45 KVM_CAP_S390_USER_OPEREXEC +---------------------------- + +:Architectures: s390 +:Parameters: none + +When this capability is enabled KVM forwards all operation exceptions +that it doesn't handle itself to user space. This also includes the +0x0000 instructions managed by KVM_CAP_S390_USER_INSTR0. This is +helpful if user space wants to emulate instructions which are not +(yet) implemented in hardware. + +This capability can be enabled dynamically even if VCPUs were already +created and are running. + 8. Other capabilities. ====================== diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h index 22cedcaea475..1e4829c70216 100644 --- a/arch/s390/include/asm/kvm_host.h +++ b/arch/s390/include/asm/kvm_host.h @@ -648,6 +648,7 @@ struct kvm_arch { int user_sigp; int user_stsi; int user_instr0; + int user_operexec; struct s390_io_adapter *adapters[MAX_S390_IO_ADAPTERS]; wait_queue_head_t ipte_wq; int ipte_lock_count; diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c index c7908950c1f4..420ae62977e2 100644 --- a/arch/s390/kvm/intercept.c +++ b/arch/s390/kvm/intercept.c @@ -471,6 +471,9 @@ static int handle_operexc(struct kvm_vcpu *vcpu) if (vcpu->arch.sie_block->ipa == 0xb256) return handle_sthyi(vcpu); + if (vcpu->kvm->arch.user_operexec) + return -EOPNOTSUPP; + if (vcpu->arch.sie_block->ipa == 0 && vcpu->kvm->arch.user_instr0) return -EOPNOTSUPP; rc = read_guest_lc(vcpu, __LC_PGM_NEW_PSW, &newpsw, sizeof(psw_t)); diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 70ebc54b1bb1..56d4730b7c41 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -606,6 +606,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_SET_GUEST_DEBUG: case KVM_CAP_S390_DIAG318: case KVM_CAP_IRQFD_RESAMPLE: + case KVM_CAP_S390_USER_OPEREXEC: r = 1; break; case KVM_CAP_SET_GUEST_DEBUG2: @@ -921,6 +922,12 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap) VM_EVENT(kvm, 3, "ENABLE: CAP_S390_CPU_TOPOLOGY %s", r ? "(not available)" : "(success)"); break; + case KVM_CAP_S390_USER_OPEREXEC: + VM_EVENT(kvm, 3, "%s", "ENABLE: CAP_S390_USER_OPEREXEC"); + kvm->arch.user_operexec = 1; + icpt_operexc_on_all_vcpus(kvm); + r = 0; + break; default: r = -EINVAL; break; diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 52f6000ab020..8ab07396ce3b 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -963,6 +963,7 @@ struct kvm_enable_cap { #define KVM_CAP_RISCV_MP_STATE_RESET 242 #define KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED 243 #define KVM_CAP_GUEST_MEMFD_FLAGS 244 +#define KVM_CAP_S390_USER_OPEREXEC 245 struct kvm_irq_routing_irqchip { __u32 irqchip; diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm index 148d427ff24b..87e429206bb8 100644 --- a/tools/testing/selftests/kvm/Makefile.kvm +++ b/tools/testing/selftests/kvm/Makefile.kvm @@ -194,6 +194,7 @@ TEST_GEN_PROGS_s390 += s390/debug_test TEST_GEN_PROGS_s390 += s390/cpumodel_subfuncs_test TEST_GEN_PROGS_s390 += s390/shared_zeropage_test TEST_GEN_PROGS_s390 += s390/ucontrol_test +TEST_GEN_PROGS_s390 += s390/user_operexec TEST_GEN_PROGS_s390 += rseq_test TEST_GEN_PROGS_riscv = $(TEST_GEN_PROGS_COMMON) diff --git a/tools/testing/selftests/kvm/s390/user_operexec.c b/tools/testing/selftests/kvm/s390/user_operexec.c new file mode 100644 index 000000000000..714906c1d12a --- /dev/null +++ b/tools/testing/selftests/kvm/s390/user_operexec.c @@ -0,0 +1,140 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Test operation exception forwarding. + * + * Copyright IBM Corp. 2025 + * + * Authors: + * Janosch Frank + */ +#include "kselftest.h" +#include "kvm_util.h" +#include "test_util.h" +#include "sie.h" + +#include + +static void guest_code_instr0(void) +{ + asm(".word 0x0000"); +} + +static void test_user_instr0(void) +{ + struct kvm_vcpu *vcpu; + struct kvm_vm *vm; + int rc; + + vm = vm_create_with_one_vcpu(&vcpu, guest_code_instr0); + rc = __vm_enable_cap(vm, KVM_CAP_S390_USER_INSTR0, 0); + TEST_ASSERT_EQ(0, rc); + + vcpu_run(vcpu); + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_S390_SIEIC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.icptcode, ICPT_OPEREXC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.ipa, 0); + + kvm_vm_free(vm); +} + +static void guest_code_user_operexec(void) +{ + asm(".word 0x0807"); +} + +static void test_user_operexec(void) +{ + struct kvm_vcpu *vcpu; + struct kvm_vm *vm; + int rc; + + vm = vm_create_with_one_vcpu(&vcpu, guest_code_user_operexec); + rc = __vm_enable_cap(vm, KVM_CAP_S390_USER_OPEREXEC, 0); + TEST_ASSERT_EQ(0, rc); + + vcpu_run(vcpu); + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_S390_SIEIC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.icptcode, ICPT_OPEREXC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.ipa, 0x0807); + + kvm_vm_free(vm); + + /* + * Since user_operexec is the superset it can be used for the + * 0 instruction. + */ + vm = vm_create_with_one_vcpu(&vcpu, guest_code_instr0); + rc = __vm_enable_cap(vm, KVM_CAP_S390_USER_OPEREXEC, 0); + TEST_ASSERT_EQ(0, rc); + + vcpu_run(vcpu); + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_S390_SIEIC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.icptcode, ICPT_OPEREXC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.ipa, 0); + + kvm_vm_free(vm); +} + +/* combine user_instr0 and user_operexec */ +static void test_user_operexec_combined(void) +{ + struct kvm_vcpu *vcpu; + struct kvm_vm *vm; + int rc; + + vm = vm_create_with_one_vcpu(&vcpu, guest_code_user_operexec); + rc = __vm_enable_cap(vm, KVM_CAP_S390_USER_INSTR0, 0); + TEST_ASSERT_EQ(0, rc); + rc = __vm_enable_cap(vm, KVM_CAP_S390_USER_OPEREXEC, 0); + TEST_ASSERT_EQ(0, rc); + + vcpu_run(vcpu); + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_S390_SIEIC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.icptcode, ICPT_OPEREXC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.ipa, 0x0807); + + kvm_vm_free(vm); + + /* Reverse enablement order */ + vm = vm_create_with_one_vcpu(&vcpu, guest_code_user_operexec); + rc = __vm_enable_cap(vm, KVM_CAP_S390_USER_OPEREXEC, 0); + TEST_ASSERT_EQ(0, rc); + rc = __vm_enable_cap(vm, KVM_CAP_S390_USER_INSTR0, 0); + TEST_ASSERT_EQ(0, rc); + + vcpu_run(vcpu); + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_S390_SIEIC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.icptcode, ICPT_OPEREXC); + TEST_ASSERT_EQ(vcpu->run->s390_sieic.ipa, 0x0807); + + kvm_vm_free(vm); +} + +/* + * Run all tests above. + * + * Enablement after VCPU has been added is automatically tested since + * we enable the capability after VCPU creation. + */ +static struct testdef { + const char *name; + void (*test)(void); +} testlist[] = { + { "instr0", test_user_instr0 }, + { "operexec", test_user_operexec }, + { "operexec_combined", test_user_operexec_combined}, +}; + +int main(int argc, char *argv[]) +{ + int idx; + + TEST_REQUIRE(kvm_has_cap(KVM_CAP_S390_USER_INSTR0)); + + ksft_print_header(); + ksft_set_plan(ARRAY_SIZE(testlist)); + for (idx = 0; idx < ARRAY_SIZE(testlist); idx++) { + testlist[idx].test(); + ksft_test_result_pass("%s\n", testlist[idx].name); + } + ksft_finished(); +} -- 2.48.1