test_pv_unhalt() only checks that KVM clears KVM_FEATURE_PV_UNHALT from guest CPUID when HLT-exiting is disabled. The feature itself has never been exercised, hence the FIXME.
Add a two vCPU test for it. The first vCPU halts with interrupts disabled, so nothing except the KVM_HC_KICK_CPU issued by the second can resume it: KVM delivers the kick as APIC_DM_REMRD, which sets pv_unhalted and makes the vCPU runnable without injecting an interrupt. Reaching the instruction after HLT is therefore proof that the kick arrived. Give the halting vCPU a non-zero APIC ID, so that a kick aimed at the wrong vCPU fails the test instead of hitting the halter by chance, and enable its APIC as a guest using PV spinlocks would, since KVM only routes the kick once the vCPU's APIC is in the map. Wait for the halter's halt_exits to tick before kicking so that the kick lands on a vCPU that has actually halted, and bound the wait so a vCPU that never halts fails the test instead of hanging it. The kicking vCPU runs with KVM_CAP_ENFORCE_PV_FEATURE_CPUID enabled and PV_UNHALT advertised, so that KVM services the hypercall because the feature is exposed rather than because enforcement is off. Assisted-by: Cursor:claude-opus-5 Signed-off-by: Hemanth Selam <[email protected]> --- tools/testing/selftests/kvm/x86/kvm_pv_test.c | 97 ++++++++++++++++++- 1 file changed, 96 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/kvm/x86/kvm_pv_test.c b/tools/testing/selftests/kvm/x86/kvm_pv_test.c index 8ed5fa635021..120d08ac25ce 100644 --- a/tools/testing/selftests/kvm/x86/kvm_pv_test.c +++ b/tools/testing/selftests/kvm/x86/kvm_pv_test.c @@ -6,8 +6,10 @@ */ #include <asm/kvm_para.h> #include <linux/kvm_para.h> +#include <pthread.h> #include <stdint.h> +#include "apic.h" #include "test_util.h" #include "kvm_util.h" #include "processor.h" @@ -193,7 +195,99 @@ static void test_pv_unhalt(void) TEST_ASSERT(!vcpu_cpuid_has(vcpu, X86_FEATURE_KVM_PV_UNHALT), "PV_UNHALT set in guest CPUID when HLT-exiting is disabled"); - /* FIXME: actually test KVM_FEATURE_PV_UNHALT feature */ + kvm_vm_free(vm); +} + +static void pv_unhalt_halter_guest_code(void) +{ + /* + * Enable the local APIC, as a guest that uses PV spinlocks would. KVM + * only routes the kick to this vCPU once its APIC is in the map. + */ + xapic_enable(); + + /* + * Interrupts are disabled, so nothing except the KVM_HC_KICK_CPU from + * the other vCPU can end the halt, i.e. reaching GUEST_DONE() proves + * the kick was delivered. + */ + asm volatile("cli; hlt"); + + GUEST_DONE(); +} + +static void pv_unhalt_kicker_guest_code(u32 halter_apic_id) +{ + /* KVM takes flags in a0 and the APIC ID to kick in a1. */ + GUEST_ASSERT_EQ(kvm_hypercall(KVM_HC_KICK_CPU, 0, halter_apic_id, 0, 0), 0); + GUEST_DONE(); +} + +static void run_guest_to_done(struct kvm_vcpu *vcpu) +{ + struct ucall uc; + u64 cmd; + + vcpu_run(vcpu); + TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO); + + cmd = get_ucall(vcpu, &uc); + if (cmd == UCALL_ABORT) + REPORT_GUEST_ASSERT(uc); + TEST_ASSERT_EQ(cmd, UCALL_DONE); +} + +static void *pv_unhalt_halter_thread(void *vcpu) +{ + run_guest_to_done(vcpu); + return NULL; +} + +static void test_pv_unhalt_kick(void) +{ + struct kvm_vcpu *halter, *kicker; + struct timespec start; + struct kvm_vm *vm; + pthread_t thread; + int r; + + pr_info("testing KVM_HC_KICK_CPU\n"); + + /* + * Give the halter a non-zero APIC ID, so that a kick sent to the wrong + * vCPU fails the test instead of hitting the halter by chance. + */ + vm = vm_create_with_one_vcpu(&kicker, pv_unhalt_kicker_guest_code); + halter = vm_vcpu_add(vm, 1, pv_unhalt_halter_guest_code); + virt_pg_map(vm, APIC_DEFAULT_GPA, APIC_DEFAULT_GPA); + + /* + * Enforce the PV CPUID so that KVM services the hypercall because + * PV_UNHALT is advertised to the kicker, and not because enforcement + * is off. KVM advertises PV_UNHALT by default while HLT-exiting is + * enabled; set it explicitly so that the test keeps testing the + * feature if that ever changes. + */ + vcpu_enable_cap(kicker, KVM_CAP_ENFORCE_PV_FEATURE_CPUID, 1); + vcpu_set_cpuid_feature(kicker, X86_FEATURE_KVM_PV_UNHALT); + vcpu_args_set(kicker, 1, vcpu_get_apic_id(halter)); + + r = pthread_create(&thread, NULL, pv_unhalt_halter_thread, halter); + TEST_ASSERT(!r, "pthread_create halter failed, error=%d", r); + + /* Kick only once the halter has taken its HLT exit. */ + clock_gettime(CLOCK_MONOTONIC, &start); + while (!vcpu_get_stat(halter, halt_exits)) { + TEST_ASSERT(timespec_elapsed(start).tv_sec < 10, + "vCPU never halted"); + usleep(100); + } + + run_guest_to_done(kicker); + + /* Nothing except the kick can get the halter to GUEST_DONE(). */ + r = pthread_join(thread, NULL); + TEST_ASSERT(!r, "pthread_join halter failed, error=%d", r); kvm_vm_free(vm); } @@ -215,4 +309,5 @@ int main(void) kvm_vm_free(vm); test_pv_unhalt(); + test_pv_unhalt_kick(); } -- 2.43.7
