Re: [RFC PATCH 1/2] KVM: arm64: nv: selftests: Add guest hypervisor test

[Marc Zyngier <maz@kernel.org>]

On Thu, 06 Feb 2025 16:41:19 +0000,
Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com> wrote:
> 
> This patch adds the required changes to init vcpu in vEL2 context.
> Also adds a KVM selftest to execute guest code as a guest hypervisor(L1).
> 
> Signed-off-by: Ganapatrao Kulkarni <gankulkarni@os.amperecomputing.com>
> ---
>  tools/testing/selftests/kvm/Makefile.kvm      |  1 +
>  .../selftests/kvm/arm64/nv_guest_hypervisor.c | 83 +++++++++++++++++++
>  .../kvm/include/arm64/kvm_util_arch.h         |  3 +
>  .../selftests/kvm/include/arm64/nv_util.h     | 28 +++++++
>  .../testing/selftests/kvm/include/kvm_util.h  |  1 +
>  .../selftests/kvm/lib/arm64/processor.c       | 59 +++++++++----
>  6 files changed, 161 insertions(+), 14 deletions(-)
>  create mode 100644 tools/testing/selftests/kvm/arm64/nv_guest_hypervisor.c
>  create mode 100644 tools/testing/selftests/kvm/include/arm64/nv_util.h
> 
> diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
> index 4277b983cace..a85d3bec9fb1 100644
> --- a/tools/testing/selftests/kvm/Makefile.kvm
> +++ b/tools/testing/selftests/kvm/Makefile.kvm
> @@ -154,6 +154,7 @@ 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/nv_guest_hypervisor
>  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/nv_guest_hypervisor.c b/tools/testing/selftests/kvm/arm64/nv_guest_hypervisor.c
> new file mode 100644
> index 000000000000..5aeefe43aff7
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/arm64/nv_guest_hypervisor.c
> @@ -0,0 +1,83 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2025 Ampere Computing LLC
> + */
> +#include <kvm_util.h>
> +#include <nv_util.h>
> +#include <processor.h>
> +#include <vgic.h>
> +
> +static void guest_code(void)
> +{
> +	if (read_sysreg(CurrentEL) == CurrentEL_EL2)
> +		GUEST_PRINTF("Executing guest code in vEL2\n");
> +	else
> +		GUEST_FAIL("Fail to run in vEL2\n");
> +
> +	GUEST_DONE();
> +}
> +
> +static void guest_undef_handler(struct ex_regs *regs)
> +{
> +	GUEST_FAIL("Unexpected exception far_el1 = 0x%lx", read_sysreg(far_el1));
> +}
> +
> +static void test_run_vcpu(struct kvm_vcpu *vcpu)
> +{
> +	struct ucall uc;
> +
> +	do {
> +		vcpu_run(vcpu);
> +
> +		switch (get_ucall(vcpu, &uc)) {
> +		case UCALL_ABORT:
> +			REPORT_GUEST_ASSERT(uc);
> +			break;
> +		case UCALL_PRINTF:
> +			printf("%s", uc.buffer);
> +			break;
> +		case UCALL_DONE:
> +			printf("Test PASS\n");
> +			break;
> +		default:
> +			TEST_FAIL("Unknown ucall %lu", uc.cmd);
> +		}
> +	} while (uc.cmd != UCALL_DONE);
> +}
> +
> +static void test_nv_guest_hypervisor(void)
> +{
> +	struct kvm_vcpu *vcpu;
> +	struct kvm_vm *vm;
> +	struct kvm_vcpu_init init;
> +	int gic_fd;
> +
> +	vm = vm_create(1);
> +	vm_ioctl(vm, KVM_ARM_PREFERRED_TARGET, &init);
> +
> +	init.features[0] = 0;
> +	init_vcpu_nested(&init);
> +	vcpu = aarch64_vcpu_add(vm, 0, &init, guest_code);
> +
> +	__TEST_REQUIRE(is_vcpu_nested(vcpu), "Failed to Enable NV");
> +
> +	vm_init_descriptor_tables(vm);
> +	vcpu_init_descriptor_tables(vcpu);
> +	gic_fd = vgic_v3_setup(vm, 1, 64);
> +	__TEST_REQUIRE(gic_fd >= 0, "Failed to create vgic-v3");
> +
> +	vm_install_sync_handler(vm, VECTOR_SYNC_CURRENT,
> +				ESR_ELx_EC_UNKNOWN, guest_undef_handler);
> +
> +	test_run_vcpu(vcpu);
> +	kvm_vm_free(vm);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	TEST_REQUIRE(kvm_has_cap(KVM_CAP_ARM_EL2));
> +
> +	test_nv_guest_hypervisor();
> +
> +	return 0;
> +}
> diff --git a/tools/testing/selftests/kvm/include/arm64/kvm_util_arch.h b/tools/testing/selftests/kvm/include/arm64/kvm_util_arch.h
> index e43a57d99b56..ab5279c24413 100644
> --- a/tools/testing/selftests/kvm/include/arm64/kvm_util_arch.h
> +++ b/tools/testing/selftests/kvm/include/arm64/kvm_util_arch.h
> @@ -2,6 +2,9 @@
>  #ifndef SELFTEST_KVM_UTIL_ARCH_H
>  #define SELFTEST_KVM_UTIL_ARCH_H
>  
> +#define CurrentEL_EL1		(1 << 2)
> +#define CurrentEL_EL2		(2 << 2)
> +
>  struct kvm_vm_arch {};
>  
>  #endif  // SELFTEST_KVM_UTIL_ARCH_H
> diff --git a/tools/testing/selftests/kvm/include/arm64/nv_util.h b/tools/testing/selftests/kvm/include/arm64/nv_util.h
> new file mode 100644
> index 000000000000..4fecf1f18554
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/include/arm64/nv_util.h
> @@ -0,0 +1,28 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) 2025 Ampere Computing
> + */
> +#ifndef SELFTEST_NV_UTIL_H
> +#define SELFTEST_NV_UTIL_H
> +
> +#include <linux/bitmap.h>
> +
> +/* NV helpers */
> +static inline void init_vcpu_nested(struct kvm_vcpu_init *init)
> +{
> +	init->features[0] |= (1 << KVM_ARM_VCPU_HAS_EL2);
> +}
> +
> +static inline bool kvm_arm_vcpu_has_el2(struct kvm_vcpu_init *init)
> +{
> +	unsigned long features = init->features[0];
> +
> +	return test_bit(KVM_ARM_VCPU_HAS_EL2, &features);
> +}
> +
> +static inline bool is_vcpu_nested(struct kvm_vcpu *vcpu)
> +{
> +	return vcpu->nested;
> +}
> +
> +#endif /* SELFTEST_NV_UTIL_H */
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 4c4e5a847f67..8c53dbc17f8f 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -58,6 +58,7 @@ struct kvm_vcpu {
>  	struct kvm_dirty_gfn *dirty_gfns;
>  	uint32_t fetch_index;
>  	uint32_t dirty_gfns_count;
> +	bool nested;
>  };
>  
>  struct userspace_mem_regions {
> diff --git a/tools/testing/selftests/kvm/lib/arm64/processor.c b/tools/testing/selftests/kvm/lib/arm64/processor.c
> index 7ba3aa3755f3..35ba2ace61a2 100644
> --- a/tools/testing/selftests/kvm/lib/arm64/processor.c
> +++ b/tools/testing/selftests/kvm/lib/arm64/processor.c
> @@ -10,6 +10,7 @@
>  
>  #include "guest_modes.h"
>  #include "kvm_util.h"
> +#include "nv_util.h"
>  #include "processor.h"
>  #include "ucall_common.h"
>  
> @@ -258,14 +259,47 @@ void virt_arch_dump(FILE *stream, struct kvm_vm *vm, uint8_t indent)
>  	}
>  }
>  
> +static void aarch64_vcpu_set_reg(struct kvm_vcpu *vcpu, uint64_t sctlr_el1,
> +			uint64_t tcr_el1, uint64_t ttbr0_el1)
> +{
> +	uint64_t fpen;
> +
> +	/*
> +	 * Enable FP/ASIMD to avoid trapping when accessing Q0-Q15
> +	 * registers, which the variable argument list macros do.
> +	 */
> +	fpen = 3 << 20;
> +
> +	if (is_vcpu_nested(vcpu)) {
> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_CPTR_EL2), fpen);
> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_SCTLR_EL2), sctlr_el1);
> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TCR_EL2), tcr_el1);
> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_MAIR_EL2), DEFAULT_MAIR_EL1);
> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TTBR0_EL2), ttbr0_el1);
> +		vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TPIDR_EL2), vcpu->id);

How about some of the basics such as HCR_EL2, MDCR_EL2? A bunch of
things there do have an impact on how the guest behaves, and relying
on defaults feels like a bad idea.

This also assumes VHE, without trying to enforce it.

Finally, how to you plan to make all the existing tests run as EL2
guests if TPIDR_EL1 isn't populated with the expected value? Surely
you need to change the read side...

	M.

-- 
Without deviation from the norm, progress is not possible.