linux-kernel - Re: [PATCH 02/13] RISC-V: KVM: Don't treat SBI HFENCE calls as NOPs

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Message-ID: <a17bf7bf-238f-4b71-8f77-6ca4fea380f8@linux.dev>
Date: Thu, 5 Jun 2025 17:11:47 -0700
From: Atish Patra <atish.patra@...ux.dev>
To: Anup Patel <apatel@...tanamicro.com>
Cc: Palmer Dabbelt <palmer@...belt.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Alexandre Ghiti <alex@...ti.fr>,
 Andrew Jones <ajones@...tanamicro.com>, Anup Patel <anup@...infault.org>,
 kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/13] RISC-V: KVM: Don't treat SBI HFENCE calls as NOPs


On 6/4/25 11:14 PM, Anup Patel wrote:
> The SBI specification clearly states that SBI HFENCE calls should
> return SBI_ERR_NOT_SUPPORTED when one of the target hart doesn’t
> support hypervisor extension (aka nested virtualization in-case
> of KVM RISC-V).
>
> Fixes: c7fa3c48de86 ("RISC-V: KVM: Treat SBI HFENCE calls as NOPs")
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> ---
>   arch/riscv/kvm/vcpu_sbi_replace.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kvm/vcpu_sbi_replace.c b/arch/riscv/kvm/vcpu_sbi_replace.c
> index 9752d2ffff68..b17fad091bab 100644
> --- a/arch/riscv/kvm/vcpu_sbi_replace.c
> +++ b/arch/riscv/kvm/vcpu_sbi_replace.c
> @@ -127,9 +127,9 @@ static int kvm_sbi_ext_rfence_handler(struct kvm_vcpu *vcpu, struct kvm_run *run
>   	case SBI_EXT_RFENCE_REMOTE_HFENCE_VVMA_ASID:
>   		/*
>   		 * Until nested virtualization is implemented, the
> -		 * SBI HFENCE calls should be treated as NOPs
> +		 * SBI HFENCE calls should return not supported
> +		 * hence fallthrough.
>   		 */
> -		break;
>   	default:
>   		retdata->err_val = SBI_ERR_NOT_SUPPORTED;
>   	}

Reviewed-by: Atish Patra <atishp@...osinc.com>