Re: [PATCH] KVM: arm64: selftest: Add standalone test checking for KVM's own UUID

[Andrew Jones <ajones@ventanamicro.com>]

Hi Marc,

On Mon, Jul 21, 2025 at 04:51:36PM +0100, Marc Zyngier wrote:
> Tinkering with UUIDs is a perilious task, and the KVM UUID gets
> broken at times. In order to spot this early enough, add a selftest
> that will shout if the expected value isn't found.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Link: https://lore.kernel.org/r/20250721130558.50823-1-jackabt.amazon@gmail.com
> ---
>  tools/testing/selftests/kvm/Makefile.kvm     |  1 +
>  tools/testing/selftests/kvm/arm64/kvm-uuid.c | 67 ++++++++++++++++++++
>  2 files changed, 68 insertions(+)
>  create mode 100644 tools/testing/selftests/kvm/arm64/kvm-uuid.c
> 
> diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
> index ce817a975e50a..e1eb1ba238a2a 100644
> --- a/tools/testing/selftests/kvm/Makefile.kvm
> +++ b/tools/testing/selftests/kvm/Makefile.kvm
> @@ -167,6 +167,7 @@ TEST_GEN_PROGS_arm64 += arm64/vgic_irq
>  TEST_GEN_PROGS_arm64 += arm64/vgic_lpi_stress
>  TEST_GEN_PROGS_arm64 += arm64/vpmu_counter_access
>  TEST_GEN_PROGS_arm64 += arm64/no-vgic-v3
> +TEST_GEN_PROGS_arm64 += arm64/kvm-uuid
>  TEST_GEN_PROGS_arm64 += access_tracking_perf_test
>  TEST_GEN_PROGS_arm64 += arch_timer
>  TEST_GEN_PROGS_arm64 += coalesced_io_test
> diff --git a/tools/testing/selftests/kvm/arm64/kvm-uuid.c b/tools/testing/selftests/kvm/arm64/kvm-uuid.c
> new file mode 100644
> index 0000000000000..89d9c8b182ae5
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/arm64/kvm-uuid.c
> @@ -0,0 +1,67 @@
> +#include <errno.h>
> +#include <linux/arm-smccc.h>
> +#include <asm/kvm.h>
> +#include <kvm_util.h>
> +
> +#include "processor.h"
> +
> +/*
> + * Do NOT redefine these constants, or try to replace them with some
> + * "common" version. They are hardcoded here to detect any potential
> + * breakage happening in the rest of the kernel.
> + *
> + * KVM UID value: 28b46fb6-2ec5-11e9-a9ca-4b564d003a74
> + */
> +#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0	0xb66fb428U
> +#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1	0xe911c52eU
> +#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2	0x564bcaa9U
> +#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3	0x743a004dU
> +
> +static void guest_code(void)
> +{
> +	struct arm_smccc_res res = {};
> +
> +	smccc_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, 0, 0, 0, 0, 0, 0, 0, &res);
> +
> +	__GUEST_ASSERT(res.a0 != SMCCC_RET_NOT_SUPPORTED, "a0 = %lx\n", res.a0);

Should this check res.a0 == SMCCC_RET_SUCCESS instead?

> +	__GUEST_ASSERT(res.a0 == ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0 &&
> +		       res.a1 == ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1 &&
> +		       res.a2 == ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2 &&
> +		       res.a3 == ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3,
> +		       "Unexpected KVM-specific UID %lx %lx %lx %lx\n", res.a0, res.a1, res.a2, res.a3);
> +	GUEST_DONE();
> +}
> +
> +int main (int argc, char *argv[])
> +{
> +	struct kvm_vcpu *vcpu;
> +	struct kvm_vm *vm;
> +	struct ucall uc;
> +	bool guest_done = false;
> +
> +	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
> +
> +	while (!guest_done) {
> +		vcpu_run(vcpu);
> +
> +		switch (get_ucall(vcpu, &uc)) {
> +		case UCALL_SYNC:
> +			break;
> +		case UCALL_DONE:
> +			guest_done = true;
> +			break;
> +		case UCALL_ABORT:
> +			REPORT_GUEST_ASSERT(uc);
> +			break;
> +		case UCALL_PRINTF:
> +			printf("%s", uc.buffer);
> +			break;
> +		default:
> +			TEST_FAIL("Unexpected guest exit");
> +		}
> +	}

This is becoming a very common and useful pattern. I wonder if it's time
for a ucall helper

static void ucall_vcpu_run(struct kvm_vcpu *vcpu,
                           void (*sync_func)(struct kvm_vcpu *, void *),
                           void *sync_data)
{
        bool guest_done = false;
        struct ucall uc;

        while (!guest_done) {
                vcpu_run(vcpu);

                switch (get_ucall(vcpu, &uc)) {
                case UCALL_SYNC:
                        if (sync_func)
                                sync_func(vcpu, sync_data);
                        break;
                case UCALL_DONE:
                        guest_done = true;
                        break;
                case UCALL_ABORT:
                        REPORT_GUEST_ASSERT(uc);
                        break;
                case UCALL_PRINTF:
                        printf("%s", uc.buffer);
                        break;
                default:
                        TEST_FAIL("Unexpected guest exit");
                }
        }
}

Thanks,
drew

> +
> +	kvm_vm_free(vm);
> +
> +	return 0;
> +}
> -- 
> 2.39.2
>