linux-kernel - Re: [PATCH 3/5] riscv: KVM: Fix SBI IPI error generation

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Message-ID: <CAAhSdy0SScanoz9Q_dm9YBP3bkoGGnM5AXGVWhtUrMcUZ9_=Nw@mail.gmail.com>
Date: Mon, 17 Feb 2025 16:13:44 +0530
From: Anup Patel <anup@...infault.org>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org, 
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	atishp@...shpatra.org, paul.walmsley@...ive.com, palmer@...belt.com, 
	aou@...s.berkeley.edu, cleger@...osinc.com
Subject: Re: [PATCH 3/5] riscv: KVM: Fix SBI IPI error generation

On Mon, Feb 17, 2025 at 2:15 PM Andrew Jones <ajones@...tanamicro.com> wrote:
>
> When an invalid function ID of an SBI extension is used we should
> return not-supported, not invalid-param. Also, when we see that at
> least one hartid constructed from the base and mask parameters is
> invalid, then we should return invalid-param. Finally, rather than
> relying on overflowing a left shift to result in zero and then using
> that zero in a condition which [correctly] skips sending an IPI (but
> loops unnecessarily), explicitly check for overflow and exit the loop
> immediately.
>
> Fixes: 5f862df5585c ("RISC-V: KVM: Add v0.1 replacement SBI extensions defined in v0.2")
> Signed-off-by: Andrew Jones <ajones@...tanamicro.com>

LGTM.

Reviewed-by: Anup Patel <anup@...infault.org>

Regards,
Anup

> ---
>  arch/riscv/kvm/vcpu_sbi_replace.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kvm/vcpu_sbi_replace.c b/arch/riscv/kvm/vcpu_sbi_replace.c
> index 9c2ab3dfa93a..74e3a38c6a29 100644
> --- a/arch/riscv/kvm/vcpu_sbi_replace.c
> +++ b/arch/riscv/kvm/vcpu_sbi_replace.c
> @@ -51,9 +51,10 @@ static int kvm_sbi_ext_ipi_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
>         struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
>         unsigned long hmask = cp->a0;
>         unsigned long hbase = cp->a1;
> +       unsigned long hart_bit = 0, sentmask = 0;
>
>         if (cp->a6 != SBI_EXT_IPI_SEND_IPI) {
> -               retdata->err_val = SBI_ERR_INVALID_PARAM;
> +               retdata->err_val = SBI_ERR_NOT_SUPPORTED;
>                 return 0;
>         }
>
> @@ -62,15 +63,23 @@ static int kvm_sbi_ext_ipi_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
>                 if (hbase != -1UL) {
>                         if (tmp->vcpu_id < hbase)
>                                 continue;
> -                       if (!(hmask & (1UL << (tmp->vcpu_id - hbase))))
> +                       hart_bit = tmp->vcpu_id - hbase;
> +                       if (hart_bit >= __riscv_xlen)
> +                               goto done;
> +                       if (!(hmask & (1UL << hart_bit)))
>                                 continue;
>                 }
>                 ret = kvm_riscv_vcpu_set_interrupt(tmp, IRQ_VS_SOFT);
>                 if (ret < 0)
>                         break;
> +               sentmask |= 1UL << hart_bit;
>                 kvm_riscv_vcpu_pmu_incr_fw(tmp, SBI_PMU_FW_IPI_RCVD);
>         }
>
> +done:
> +       if (hbase != -1UL && (hmask ^ sentmask))
> +               retdata->err_val = SBI_ERR_INVALID_PARAM;
> +
>         return ret;
>  }
>
> --
> 2.48.1
>