linux-kernel - Re: [PATCH v6 2/2] RISC-V: KVM: selftests: Add RISC-V SBI STA shmem alignment tests

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Message-ID: <gcspbbvqkr7y53c4ytkqqycygkcqkiakle4aelq2z7nsnlyegl@addv4v655cbg>
Date: Thu, 5 Feb 2026 09:58:15 -0600
From: Andrew Jones <andrew.jones@....qualcomm.com>
To: Jiakai Xu <xujiakai2025@...as.ac.cn>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-kselftest@...r.kernel.org, Anup Patel <anup@...infault.org>,
        Atish Patra <atish.patra@...ux.dev>, Paul Walmsley <pjw@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
        Alexandre Ghiti <alex@...ti.fr>,
        Andrew Jones <ajones@...tanamicro.com>,
        Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>,
        Jiakai Xu <jiakaiPeanut@...il.com>
Subject: Re: [PATCH v6 2/2] RISC-V: KVM: selftests: Add RISC-V SBI STA shmem
 alignment tests

On Thu, Feb 05, 2026 at 01:05:02AM +0000, Jiakai Xu wrote:
> Add RISC-V KVM selftests to verify the SBI Steal-Time Accounting (STA)
> shared memory alignment requirements.
> 
> The SBI specification requires the STA shared memory GPA to be 64-byte
> aligned, or set to all-ones to explicitly disable steal-time accounting.
> This test verifies that KVM enforces the expected behavior when
> configuring the SBI STA shared memory via KVM_SET_ONE_REG.
> 
> Specifically, the test checks that:
> - misaligned GPAs are rejected with -EINVAL
> - 64-byte aligned GPAs are accepted
> - INVALID_GPA correctly disables steal-time accounting
> 
> Signed-off-by: Jiakai Xu <xujiakai2025@...as.ac.cn>
> Signed-off-by: Jiakai Xu <jiakaiPeanut@...il.com>
> ---
>  .../selftests/kvm/include/riscv/processor.h   |  4 +++
>  tools/testing/selftests/kvm/steal_time.c      | 33 +++++++++++++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/riscv/processor.h b/tools/testing/selftests/kvm/include/riscv/processor.h
> index e58282488beb3..c3551d129d2f6 100644
> --- a/tools/testing/selftests/kvm/include/riscv/processor.h
> +++ b/tools/testing/selftests/kvm/include/riscv/processor.h
> @@ -62,6 +62,10 @@ static inline uint64_t __kvm_reg_id(uint64_t type, uint64_t subtype,
>  						     KVM_REG_RISCV_SBI_SINGLE,		\
>  						     idx, KVM_REG_SIZE_ULONG)
>  
> +#define RISCV_SBI_STA_REG(idx)	__kvm_reg_id(KVM_REG_RISCV_SBI_STATE,	\
> +						     KVM_REG_RISCV_SBI_STA,			\
> +						     idx, KVM_REG_SIZE_ULONG)

We don't need this because...

> +
>  bool __vcpu_has_ext(struct kvm_vcpu *vcpu, uint64_t ext);
>  
>  static inline bool __vcpu_has_isa_ext(struct kvm_vcpu *vcpu, uint64_t isa_ext)
> diff --git a/tools/testing/selftests/kvm/steal_time.c b/tools/testing/selftests/kvm/steal_time.c
> index 8edc1fca345ba..30b98d1b601c3 100644
> --- a/tools/testing/selftests/kvm/steal_time.c
> +++ b/tools/testing/selftests/kvm/steal_time.c
> @@ -209,6 +209,7 @@ static void steal_time_dump(struct kvm_vm *vm, uint32_t vcpu_idx)
>  
>  /* SBI STA shmem must have 64-byte alignment */
>  #define STEAL_TIME_SIZE		((sizeof(struct sta_struct) + 63) & ~63)
> +#define INVALID_GPA (~(u64)0)
>  
>  static vm_paddr_t st_gpa[NR_VCPUS];
>  
> @@ -301,6 +302,34 @@ static void steal_time_dump(struct kvm_vm *vm, uint32_t vcpu_idx)
>  	pr_info("\n");
>  }
>  
> +static void test_riscv_sta_shmem_alignment(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_one_reg reg;
> +	uint64_t shmem;
> +	int ret;
> +
> +	reg.id = RISCV_SBI_STA_REG(0);

...here we should use KVM_REG_RISCV_SBI_STA_REG(shmem_lo)

> +	reg.addr = (uint64_t)&shmem;
> +
> +	/* Case 1: misaligned GPA */
> +	shmem = ST_GPA_BASE + 1;
> +	ret = __vcpu_ioctl(vcpu, KVM_SET_ONE_REG, &reg);
> +	TEST_ASSERT(ret == -1 && errno == EINVAL,
> +		    "misaligned STA shmem should return -EINVAL");

remove the word 'should'

"misaligned STA shmem returns -EINVAL"

> +
> +	/* Case 2: 64-byte aligned GPA */
> +	shmem = ST_GPA_BASE;
> +	ret = __vcpu_ioctl(vcpu, KVM_SET_ONE_REG, &reg);
> +	TEST_ASSERT(ret == 0,
> +		    "aligned STA shmem should succeed");

same comment about 'should'

> +
> +	/* Case 3: INVALID_GPA disables STA */
> +	shmem = INVALID_GPA;
> +	ret = __vcpu_ioctl(vcpu, KVM_SET_ONE_REG, &reg);
> +	TEST_ASSERT(ret == 0,
> +		    "INVALID_GPA should disable STA successfully");

We're not testing that STA was successfully disabled, only that all-ones
input doesn't generate an error. So the message should be along the lines
of "all-ones for STA shmem succeeds"

> +}
> +
>  #endif
>  
>  static void *do_steal_time(void *arg)
> @@ -369,6 +398,10 @@ int main(int ac, char **av)
>  	TEST_REQUIRE(is_steal_time_supported(vcpus[0]));
>  	ksft_set_plan(NR_VCPUS);
>  
> +#ifdef __riscv
> +	test_riscv_sta_shmem_alignment(vcpus[0]);
> +#endif

We like to try to avoid #ifdefs in common functions by providing stubs for
architectures that don't need them [yet]. So we should rename this to
something more generic, like

 check_steal_time_uapi()

and then call it for all architectures. Actually the other architectures
can already make use of it since both x86 and arm64 do uapi tests in
their steal_time_init() functions and that's not really the right
place to do that. I suggest creating another patch that first moves those
tests into new functions (check_steal_time_uapi()) which only needs to
be called once for vcpu[0] outside the vcpu loop, as you do here. In
that patch check_steal_time_uapi() will be a stub for riscv. Then in 
a second patch fill in that stub with the tests above.

Thanks,
drew

> +
>  	/* Run test on each VCPU */
>  	for (i = 0; i < NR_VCPUS; ++i) {
>  		steal_time_init(vcpus[i], i);
> -- 
> 2.34.1
>