linux-kernel - Re: [PATCH 3/4] KVM: riscv: selftests: Add guest helper to get vcpu id

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Message-ID: <20230728-42019a78766a59dc5abdd412@orel>
Date:   Fri, 28 Jul 2023 11:49:11 +0200
From:   Andrew Jones <ajones@...tanamicro.com>
To:     Haibo Xu <haibo1.xu@...el.com>
Cc:     xiaobo55x@...il.com, Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        Andrew Jones <andrew.jones@...ux.dev>,
        Vipin Sharma <vipinsh@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Vishal Annapurve <vannapurve@...gle.com>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        kvm-riscv@...ts.infradead.org
Subject: Re: [PATCH 3/4] KVM: riscv: selftests: Add guest helper to get vcpu
 id

On Thu, Jul 27, 2023 at 03:20:07PM +0800, Haibo Xu wrote:
> Add guest_get_vcpuid() helper to simplify accessing to per-cpu
> private data. The sscratch CSR was used to store the vcpu id.
> 
> Signed-off-by: Haibo Xu <haibo1.xu@...el.com>
> ---
>  tools/testing/selftests/kvm/include/riscv/processor.h | 2 ++
>  tools/testing/selftests/kvm/lib/riscv/processor.c     | 8 ++++++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/riscv/processor.h b/tools/testing/selftests/kvm/include/riscv/processor.h
> index 9ea6e7bedc61..ca53570ce6de 100644
> --- a/tools/testing/selftests/kvm/include/riscv/processor.h
> +++ b/tools/testing/selftests/kvm/include/riscv/processor.h
> @@ -165,4 +165,6 @@ struct sbiret sbi_ecall(int ext, int fid, unsigned long arg0,
>  			unsigned long arg3, unsigned long arg4,
>  			unsigned long arg5);
>  
> +uint32_t guest_get_vcpuid(void);

I'd also put this prototype somewhere common.

> +
>  #endif /* SELFTEST_KVM_PROCESSOR_H */
> diff --git a/tools/testing/selftests/kvm/lib/riscv/processor.c b/tools/testing/selftests/kvm/lib/riscv/processor.c
> index f1b0be58a5dc..b8ad3e69a697 100644
> --- a/tools/testing/selftests/kvm/lib/riscv/processor.c
> +++ b/tools/testing/selftests/kvm/lib/riscv/processor.c
> @@ -316,6 +316,9 @@ struct kvm_vcpu *vm_arch_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id,
>  	vcpu_set_reg(vcpu, RISCV_CORE_REG(regs.sp), stack_vaddr + stack_size);
>  	vcpu_set_reg(vcpu, RISCV_CORE_REG(regs.pc), (unsigned long)guest_code);
>  
> +	/* Setup scratch regiter of guest */

typo: register

The comment above is pretty useless since it just states what the code
states, but with even less information, since it doesn't state how the
sscratch register is getting set up. I'd either drop it or write it
as

 /* Setup sscratch for guest_get_vcpuid() */

> +	vcpu_set_reg(vcpu, RISCV_CSR_REG(sscratch), vcpu_id);
> +
>  	/* Setup default exception vector of guest */
>  	vcpu_set_reg(vcpu, RISCV_CSR_REG(stvec), (unsigned long)guest_unexp_trap);
>  
> @@ -424,3 +427,8 @@ void vm_install_interrupt_handler(struct kvm_vm *vm, void (*handler)(struct ex_r
>  
>  	handlers->exception_handlers[1][0] = handler;
>  }
> +
> +uint32_t guest_get_vcpuid(void)
> +{
> +	return csr_read(CSR_SSCRATCH);
> +}
> -- 
> 2.34.1
>

Thanks,
drew