[PATCH v3 3/3] RISC-V: KVM: selftests: Add ebreak test support

[Andrew Jones]

On Wed, Mar 27, 2024 at 07:55:26AM +0000, Chao Du wrote:
> Initial support for RISC-V KVM ebreak test. Check the exit reason and
> the PC when guest debug is enabled. Also to make sure the guest could
> handle the ebreak exception without exiting to the VMM when guest debug
> is not enabled.
> 
> Signed-off-by: Chao Du <duchao at eswincomputing.com>
> ---
>  tools/testing/selftests/kvm/Makefile          |  1 +
>  .../testing/selftests/kvm/riscv/ebreak_test.c | 84 +++++++++++++++++++
>  2 files changed, 85 insertions(+)
>  create mode 100644 tools/testing/selftests/kvm/riscv/ebreak_test.c
> 
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 741c7dc16afc..7f4430242c9e 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -189,6 +189,7 @@ TEST_GEN_PROGS_s390x += rseq_test
>  TEST_GEN_PROGS_s390x += set_memory_region_test
>  TEST_GEN_PROGS_s390x += kvm_binary_stats_test
>  
> +TEST_GEN_PROGS_riscv += riscv/ebreak_test
>  TEST_GEN_PROGS_riscv += arch_timer
>  TEST_GEN_PROGS_riscv += demand_paging_test
>  TEST_GEN_PROGS_riscv += dirty_log_test
> diff --git a/tools/testing/selftests/kvm/riscv/ebreak_test.c b/tools/testing/selftests/kvm/riscv/ebreak_test.c
> new file mode 100644
> index 000000000000..4c79c778e026
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/riscv/ebreak_test.c
> @@ -0,0 +1,84 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * RISC-V KVM ebreak test.
> + *
> + * Copyright 2024 Beijing ESWIN Computing Technology Co., Ltd.
> + *
> + */
> +#include "kvm_util.h"
> +
> +#define PC(v) ((uint64_t)&(v))

PC() isn't a good name for the function this is doing. It's getting
the address of a label. LABEL_ADDRESS() would be more appropriate.

> +
> +extern unsigned char sw_bp_1, sw_bp_2;
> +static volatile uint64_t sw_bp_addr;

Drop volatile here and use READ/WRITE_ONCE on sw_bp_addr when reading and
writing it.

> +
> +static void guest_code(void)
> +{
> +	/*
> +	 * nops are inserted to make sure that the "pc += 4" operation is
> +	 * compatible with the compressed instructions.
> +	 */
> +	asm volatile("sw_bp_1: ebreak\n"
> +		     "nop\n"
> +		     "sw_bp_2: ebreak\n"
> +		     "nop\n");

The nops are fine, but options should work too, something like

 asm volatile(
 ".option push\n"
 ".option norvc\n"
 "sw_bp_1: ebreak\n"
 "sw_bp_2: ebreak\n"
 ".option pop\n"
 );

> +	GUEST_ASSERT_EQ(sw_bp_addr, PC(sw_bp_2));
> +
> +	GUEST_DONE();
> +}
> +
> +static void guest_breakpoint_handler(struct ex_regs *regs)
> +{
> +	sw_bp_addr = regs->epc;
> +	regs->epc += 4;
> +}
> +
> +int main(void)
> +{
> +	struct kvm_vm *vm;
> +	struct kvm_vcpu *vcpu;
> +	uint64_t pc;
> +	struct kvm_guest_debug debug = {
> +		.control = KVM_GUESTDBG_ENABLE,
> +	};
> +	struct ucall uc;

You don't use 'uc', so you can drop it and...

> +
> +	TEST_REQUIRE(kvm_has_cap(KVM_CAP_SET_GUEST_DEBUG));
> +
> +	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
> +
> +	vm_init_vector_tables(vm);
> +	vcpu_init_vector_tables(vcpu);
> +	vm_install_exception_handler(vm, EXC_BREAKPOINT,
> +					guest_breakpoint_handler);
> +
> +	/*
> +	 * Enable the guest debug.
> +	 * ebreak should exit to the VMM with KVM_EXIT_DEBUG reason.
> +	 */
> +	vcpu_guest_debug_set(vcpu, &debug);
> +	vcpu_run(vcpu);
> +
> +	TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_DEBUG);
> +
> +	vcpu_get_reg(vcpu, RISCV_CORE_REG(regs.pc), &pc);
> +	TEST_ASSERT_EQ(pc, PC(sw_bp_1));
> +
> +	/* skip sw_bp_1 */
> +	vcpu_set_reg(vcpu, RISCV_CORE_REG(regs.pc), pc + 4);
> +
> +	/*
> +	 * Disable all debug controls.
> +	 * Guest should handle the ebreak without exiting to the VMM.
> +	 */
> +	memset(&debug, 0, sizeof(debug));
> +	vcpu_guest_debug_set(vcpu, &debug);
> +
> +	vcpu_run(vcpu);
> +
> +	TEST_ASSERT_EQ(get_ucall(vcpu, &uc), UCALL_DONE);

...call get_ucall() with NULL for the second parameter.

> +
> +	kvm_vm_free(vm);
> +
> +	return 0;
> +}
> -- 
> 2.17.1
>

Thanks,
drew