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

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Message-ID: <CAAhSdy1kRHEBoKMSd2OYWj6fHZHU1HQq+68-H3=cJGNTF=5WLg@mail.gmail.com>
Date: Mon, 9 Jun 2025 10:13:24 +0530
From: Anup Patel <anup@...infault.org>
To: Anup Patel <apatel@...tanamicro.com>
Cc: Atish Patra <atish.patra@...ux.dev>, Palmer Dabbelt <palmer@...belt.com>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Alexandre Ghiti <alex@...ti.fr>, 
	Andrew Jones <ajones@...tanamicro.com>, 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 Thu, Jun 5, 2025 at 11:45 AM Anup Patel <apatel@...tanamicro.com> 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>

Queued as a fix for Linux-6.16

Regards,
Anup

> ---
>  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;
>         }
> --
> 2.43.0
>