[PATCH] RISC-V: KVM: Fix SBI_FWFT_POINTER_MASKING_PMLEN algorithm

[Andrew Jones]

On Sun, Sep 14, 2025 at 10:34:20PM -0700, Samuel Holland wrote:
> The implementation of SBI_FWFT_POINTER_MASKING_PMLEN from commit
> aa04d131b88b ("RISC-V: KVM: Add support for SBI_FWFT_POINTER_MASKING_PMLEN")
> was based on a draft of the SBI 3.0 specification, and is not compliant
> with the ratified version.
> 
> Update the algorithm to be compliant. Specifically, do not fall back to
> a pointer masking mode with a larger PMLEN if the mode with the
> requested PMLEN is unsupported by the hardware.
> 
> Fixes: aa04d131b88b ("RISC-V: KVM: Add support for SBI_FWFT_POINTER_MASKING_PMLEN")
> Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
> ---
> I saw that the RFC version of this patch already made it into
> riscv_kvm_queue, but it needs an update for ratified SBI 3.0. Feel free
> to squash this into the original commit, or I can send a replacement v2
> patch if you prefer.
> 
>  arch/riscv/kvm/vcpu_sbi_fwft.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/riscv/kvm/vcpu_sbi_fwft.c b/arch/riscv/kvm/vcpu_sbi_fwft.c
> index cacb3d4410a54..62cc9c3d57599 100644
> --- a/arch/riscv/kvm/vcpu_sbi_fwft.c
> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
> @@ -160,14 +160,23 @@ static long kvm_sbi_fwft_set_pointer_masking_pmlen(struct kvm_vcpu *vcpu,
>  	struct kvm_sbi_fwft *fwft = vcpu_to_fwft(vcpu);
>  	unsigned long pmm;
>  
> -	if (value == 0)
> +	switch (value) {
> +	case 0:
>  		pmm = ENVCFG_PMM_PMLEN_0;
> -	else if (value <= 7 && fwft->have_vs_pmlen_7)
> +		break;
> +	case 7:
> +		if (!fwft->have_vs_pmlen_7)
> +			return SBI_ERR_INVALID_PARAM;
>  		pmm = ENVCFG_PMM_PMLEN_7;
> -	else if (value <= 16 && fwft->have_vs_pmlen_16)
> +		break;
> +	case 16:
> +		if (!fwft->have_vs_pmlen_16)
> +			return SBI_ERR_INVALID_PARAM;
>  		pmm = ENVCFG_PMM_PMLEN_16;
> -	else
> +		break;
> +	default:
>  		return SBI_ERR_INVALID_PARAM;
> +	}
>  
>  	vcpu->arch.cfg.henvcfg &= ~ENVCFG_PMM;
>  	vcpu->arch.cfg.henvcfg |= pmm;
> -- 
> 2.47.2
> 
> base-commit: 7835b892d1d9f52fb61537757aa446fb44984215
> branch: up/kvm-fwft-pmlen
>

Reviewed-by: Andrew Jones <ajones at ventanamicro.com>