linux-kernel - Re: [PATCH v4 04/14] RISC-V: KVM: Define a probe function for SBI extension data structures

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Date:   Thu, 2 Feb 2023 16:14:33 +0100
From:   Andrew Jones <ajones@...tanamicro.com>
To:     Atish Patra <atishp@...osinc.com>
Cc:     linux-kernel@...r.kernel.org, Anup Patel <anup@...infault.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atishp@...shpatra.org>,
        Eric Lin <eric.lin@...ive.com>, Guo Ren <guoren@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
        linux-riscv@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH v4 04/14] RISC-V: KVM: Define a probe function for SBI
 extension data structures

On Wed, Feb 01, 2023 at 03:12:40PM -0800, Atish Patra wrote:
> Currently the probe function just checks if an SBI extension is
> registered or not. However, the extension may not want to advertise
> itself depending on some other condition.
> An additional extension specific probe function will allow
> extensions to decide if they want to be advertised to the caller or
> not. Any extension that does not require additional dependency checks
> can avoid implementing this function.
> 
> Reviewed-by: Anup Patel <anup@...infault.org>
> Signed-off-by: Atish Patra <atishp@...osinc.com>
> ---
>  arch/riscv/include/asm/kvm_vcpu_sbi.h |  3 +++
>  arch/riscv/kvm/vcpu_sbi_base.c        | 13 +++++++++++--
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> index f79478a..45ba341 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
> @@ -29,6 +29,9 @@ struct kvm_vcpu_sbi_extension {
>  	int (*handler)(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  		       unsigned long *out_val, struct kvm_cpu_trap *utrap,
>  		       bool *exit);
> +
> +	/* Extension specific probe function */
> +	unsigned long (*probe)(struct kvm_vcpu *vcpu);
>  };
>  
>  void kvm_riscv_vcpu_sbi_forward(struct kvm_vcpu *vcpu, struct kvm_run *run);
> diff --git a/arch/riscv/kvm/vcpu_sbi_base.c b/arch/riscv/kvm/vcpu_sbi_base.c
> index 5d65c63..846d518 100644
> --- a/arch/riscv/kvm/vcpu_sbi_base.c
> +++ b/arch/riscv/kvm/vcpu_sbi_base.c
> @@ -19,6 +19,7 @@ static int kvm_sbi_ext_base_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  {
>  	int ret = 0;
>  	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
> +	const struct kvm_vcpu_sbi_extension *sbi_ext;
>  
>  	switch (cp->a6) {
>  	case SBI_EXT_BASE_GET_SPEC_VERSION:
> @@ -43,8 +44,16 @@ static int kvm_sbi_ext_base_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  			 */
>  			kvm_riscv_vcpu_sbi_forward(vcpu, run);
>  			*exit = true;
> -		} else
> -			*out_val = kvm_vcpu_sbi_find_ext(cp->a0) ? 1 : 0;
> +		} else {
> +			sbi_ext = kvm_vcpu_sbi_find_ext(cp->a0);
> +			if (sbi_ext) {
> +				if (sbi_ext->probe)
> +					*out_val = sbi_ext->probe(vcpu);
> +				else
> +					*out_val = 1;
> +			} else
> +				*out_val = 0;

Conor points out elsewhere that we need {} on both arms if one arm needs
it. We actually don't need {} on either arm, though, or even the if, if
we rewrite as

 *out_val = sbi_ext && sbi_ext->probe ? sbi_ext->probe(vcpu) : !!sbi_ext;

Thanks,
drew

> +		}
>  		break;
>  	case SBI_EXT_BASE_GET_MVENDORID:
>  		*out_val = vcpu->arch.mvendorid;
> -- 
> 2.25.1
>