Re: [PATCH v2 3/3] RISC-V: KVM: selftests: Add breakpoints test support

From: "Chao Du" <duchao@eswincomputing.com>
To: "Andrew Jones" <ajones@ventanamicro.com>
Cc: kvm@vger.kernel.org, kvm-riscv@lists.infradead.org,
	anup@brainfault.org,  atishp@atishpatra.org, pbonzini@redhat.com,
	shuah@kernel.org,  dbarboza@ventanamicro.com,
	paul.walmsley@sifive.com,  palmer@dabbelt.com,
	aou@eecs.berkeley.edu, duchao713@qq.com
Subject: Re: [PATCH v2 3/3] RISC-V: KVM: selftests: Add breakpoints test support
Date: Fri, 1 Mar 2024 17:43:37 +0800 (GMT+08:00)	[thread overview]
Message-ID: <53c9d1f0.1501.18df965d8ca.Coremail.duchao@eswincomputing.com> (raw)
In-Reply-To: <20240301-16a75ed14197d3c5e0e7251e@orel>

On 2024-03-01 17:24, Andrew Jones <ajones@ventanamicro.com> wrote:
> 
> On Fri, Mar 01, 2024 at 01:35:45AM +0000, Chao Du wrote:
> > Initial support for RISC-V KVM breakpoint test. Check the exit reason
> > and the PC when guest debug is enabled.
> > 
> > Signed-off-by: Chao Du <duchao@eswincomputing.com>
> > ---
> >  tools/testing/selftests/kvm/Makefile          |  1 +
> >  .../testing/selftests/kvm/riscv/breakpoints.c | 49 +++++++++++++++++++
> >  2 files changed, 50 insertions(+)
> >  create mode 100644 tools/testing/selftests/kvm/riscv/breakpoints.c
> > 
> > diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> > index 492e937fab00..5f9048a740b0 100644
> > --- a/tools/testing/selftests/kvm/Makefile
> > +++ b/tools/testing/selftests/kvm/Makefile
> > @@ -184,6 +184,7 @@ 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/breakpoints
> >  TEST_GEN_PROGS_riscv += demand_paging_test
> >  TEST_GEN_PROGS_riscv += dirty_log_test
> >  TEST_GEN_PROGS_riscv += get-reg-list
> > diff --git a/tools/testing/selftests/kvm/riscv/breakpoints.c b/tools/testing/selftests/kvm/riscv/breakpoints.c
> > new file mode 100644
> > index 000000000000..be2d94837c83
> > --- /dev/null
> > +++ b/tools/testing/selftests/kvm/riscv/breakpoints.c
> > @@ -0,0 +1,49 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * RISC-V KVM breakpoint tests.
> > + *
> > + * Copyright 2024 Beijing ESWIN Computing Technology Co., Ltd.
> > + *
> > + */
> > +#include "kvm_util.h"
> > +
> > +#define PC(v) ((uint64_t)&(v))
> > +
> > +extern unsigned char sw_bp;
> > +
> > +static void guest_code(void)
> > +{
> > +	asm volatile("sw_bp: ebreak");
> > +	asm volatile("nop");
> > +	asm volatile("nop");
> > +	asm volatile("nop");
> 
> What are the nops for? And, since they're all in their own asm()'s the
> compiler could be inserting instructions between them and also the ebreak
> above. If we need three nops immediately following the ebreak then we
> need to put everything in one asm()
> 
>   asm volatile(
>   "sw_bp:	ebreak\n"
>   "		nop\n"
>   "		nop\n"
>   "		nop\n");
> 

Actually the nops have no special purpose, I will remove and just keep the
ebreak here.

> > +
> > +	GUEST_DONE();
> > +}
> > +
> > +int main(void)
> > +{
> > +	struct kvm_vm *vm;
> > +	struct kvm_vcpu *vcpu;
> > +	struct kvm_guest_debug debug;
> > +	uint64_t pc;
> > +
> > +	TEST_REQUIRE(kvm_has_cap(KVM_CAP_SET_GUEST_DEBUG));
> > +
> > +	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
> > +
> > +	memset(&debug, 0, sizeof(debug));
> > +	debug.control = KVM_GUESTDBG_ENABLE;
> 
> nit: The above two lines can be removed if we initialize debug as
> 
>   struct kvm_guest_debug debug = {
>      .control = KVM_GUESTDBG_ENABLE,
>   };
> 

Yeah, I will do so in the next patch.

> > +	vcpu_guest_debug_set(vcpu, &debug);
> > +	vcpu_run(vcpu);
> > +
> > +	TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_DEBUG);
> 
> As Anup pointed out, we need to also ensure that without making the
> KVM_SET_GUEST_DEBUG ioctl call we get the expected behavior. You
> can use GUEST_SYNC() in the guest code to prove that it was able to
> issue an ebreak without exiting to the VMM.
> 

Sure, will cover that case also.

> > +
> > +	vcpu_get_reg(vcpu, RISCV_CORE_REG(regs.pc), &pc);
> > +
> > +	TEST_ASSERT_EQ(pc, PC(sw_bp));
> > +
> > +	kvm_vm_free(vm);
> > +
> > +	return 0;
> > +}
> > -- 
> > 2.17.1
> >
> 
> Thanks,
> drew