Messages in this thread Patch in this message | | | Date | Thu, 3 Aug 2023 17:42:26 -0700 | Subject | [PATCH 4/4] KVM: selftests: Add logic to detect if ioctl() failed because VM was killed | From | Sean Christopherson <> |
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Add yet another macro to the VM/vCPU ioctl() framework to detect when an ioctl() failed because KVM killed/bugged the VM, i.e. when there was nothing wrong with the ioctl() itself. If KVM kills a VM, e.g. by way of a failed KVM_BUG_ON(), all subsequent VM and vCPU ioctl()s will fail with -EIO, which can be quite misleading and ultimately waste user/developer time.
Use KVM_CHECK_EXTENSION on KVM_CAP_USER_MEMORY to detect if the VM is dead and/or bug, as KVM doesn't provide a dedicated ioctl(). Using a heuristic is obviously less than ideal, but practically speaking the logic is bulletproof barring a KVM change, and any such change would arguably break userspace, e.g. if KVM returns something other than -EIO.
Without the detection, tearing down a bugged VM yields a cryptic failure when deleting memslots:
==== Test Assertion Failure ==== lib/kvm_util.c:689: !ret pid=45131 tid=45131 errno=5 - Input/output error 1 0x00000000004036c3: __vm_mem_region_delete at kvm_util.c:689 2 0x00000000004042f0: kvm_vm_free at kvm_util.c:724 (discriminator 12) 3 0x0000000000402929: race_sync_regs at sync_regs_test.c:193 4 0x0000000000401cab: main at sync_regs_test.c:334 (discriminator 6) 5 0x0000000000416f13: __libc_start_call_main at libc-start.o:? 6 0x000000000041855f: __libc_start_main_impl at ??:? 7 0x0000000000401d40: _start at ??:? KVM_SET_USER_MEMORY_REGION failed, rc: -1 errno: 5 (Input/output error)
Which morphs into a more pointed error message with the detection:
==== Test Assertion Failure ==== lib/kvm_util.c:689: false pid=80347 tid=80347 errno=5 - Input/output error 1 0x00000000004039ab: __vm_mem_region_delete at kvm_util.c:689 (discriminator 5) 2 0x0000000000404660: kvm_vm_free at kvm_util.c:724 (discriminator 12) 3 0x0000000000402ac9: race_sync_regs at sync_regs_test.c:193 4 0x0000000000401cb7: main at sync_regs_test.c:334 (discriminator 6) 5 0x0000000000418263: __libc_start_call_main at libc-start.o:? 6 0x00000000004198af: __libc_start_main_impl at ??:? 7 0x0000000000401d90: _start at ??:? KVM killed/bugged the VM, check the kernel log for clues
Suggested-by: Michal Luczaj <mhal@rbox.co> Signed-off-by: Sean Christopherson <seanjc@google.com> --- .../selftests/kvm/include/kvm_util_base.h | 34 ++++++++++++++++--- 1 file changed, 30 insertions(+), 4 deletions(-)
diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h index b35b0bd23683..49ad681d2161 100644 --- a/tools/testing/selftests/kvm/include/kvm_util_base.h +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h @@ -269,18 +269,44 @@ static __always_inline void static_assert_is_vm(struct kvm_vm *vm) { } kvm_do_ioctl((vm)->fd, cmd, arg); \ }) +/* + * Assert that a VM or vCPU ioctl() succeeded, with extra magic to detect if + * the ioctl() failed because KVM killed/bugged the VM. To detect a dead VM, + * probe KVM_CAP_USER_MEMORY, which (a) has been supported by KVM since before + * selftests existed and (b) should never outright fail, i.e. is supposed to + * return 0 or 1. If KVM kills a VM, KVM returns -EIO for all ioctl()s for the + * VM and its vCPUs, including KVM_CHECK_EXTENSION. + */ +#define TEST_ASSERT_VM_VCPU_IOCTL(cond, name, ret, vm) \ +do { \ + int __errno = errno; \ + \ + static_assert_is_vm(vm); \ + \ + if (cond) \ + break; \ + \ + if (errno == EIO && \ + __vm_ioctl(vm, KVM_CHECK_EXTENSION, (void *)KVM_CAP_USER_MEMORY) < 0) { \ + TEST_ASSERT(errno == EIO, "KVM killed the VM, should return -EIO"); \ + TEST_FAIL("KVM killed/bugged the VM, check the kernel log for clues"); \ + } \ + errno = __errno; \ + TEST_ASSERT(cond, __KVM_IOCTL_ERROR(name, ret)); \ +} while (0) + #define vm_ioctl(vm, cmd, arg) \ ({ \ int ret = __vm_ioctl(vm, cmd, arg); \ \ - TEST_ASSERT(!ret, __KVM_IOCTL_ERROR(#cmd, ret)); \ + TEST_ASSERT_VM_VCPU_IOCTL(!ret, #cmd, ret, vm); \ }) #define vm_fd_ioctl(vm, cmd, arg) \ ({ \ int fd = __vm_ioctl(vm, cmd, arg); \ \ - TEST_ASSERT(fd >= 0, __KVM_IOCTL_ERROR(#cmd, fd)); \ + TEST_ASSERT_VM_VCPU_IOCTL(fd >= 0, #cmd, fd, vm); \ fd; \ }) @@ -296,14 +322,14 @@ static __always_inline void static_assert_is_vcpu(struct kvm_vcpu *vcpu) { } ({ \ int ret = __vcpu_ioctl(vcpu, cmd, arg); \ \ - TEST_ASSERT(!ret, __KVM_IOCTL_ERROR(#cmd, ret)); \ + TEST_ASSERT_VM_VCPU_IOCTL(!ret, #cmd, ret, (vcpu)->vm); \ }) #define vcpu_fd_ioctl(vcpu, cmd, arg) \ ({ \ int fd = __vcpu_ioctl(vcpu, cmd, arg); \ \ - TEST_ASSERT(fd >= 0, __KVM_IOCTL_ERROR(#cmd, fd)); \ + TEST_ASSERT_VM_VCPU_IOCTL(fd >= 0, #cmd, fd, (vcpu)->vm);\ fd; \ }) -- 2.41.0.585.gd2178a4bd4-goog
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