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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 31/10/2025 09.45, Janosch Frank wrote: > On 10/30/25 08:10, Thomas Huth wrote: >> On 29/10/2025 14.04, Janosch Frank wrote: >>> 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 >> ... >>> +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 do not (yet) >>> +have an opcode. >> >> "which do not (yet) have an opcode" sounds a little bit weird. Maybe rather: >> "which are not (yet) implemented in the current CPU" or so? > > How about: > ...which are not (yet) implemented in hardware. Sounds good! >>> @@ -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); >> >> Maybe check cap->flags here and return with an error if any flag is set? ... >> otherwise, if we ever add flags here, userspace cannot check whether the >> kernel accepted a flag or not. > > Check the top of the function :) Ah, I missed that, so it should already be fine! >>> + * 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(); >>> +} >> >> You could likely use the KVM_ONE_VCPU_TEST() macro and test_harness_run() to >> get rid of the boilerplate code here. > > Is there a general directive to use KVM_ONE_VCPU_TEST? Certainly not from my side! (but Sean might have a different opinion on this topic ;-)) > To be honest I prefer the look as is since it doesn't hide things behind > macros and 95% of our tests use it. Fine for me, too. Thomas