linux-kernel - Re: [PATCH v3 2/2] RISC-V: KVM: Redirect illegal instruction traps to guest

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Date:   Thu, 2 Feb 2023 14:19:44 +0530
From:   Anup Patel <anup@...infault.org>
To:     Anup Patel <apatel@...tanamicro.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Atish Patra <atishp@...shpatra.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Andrew Jones <ajones@...tanamicro.com>, kvm@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Andy Chiu <andy.chiu@...ive.com>
Subject: Re: [PATCH v3 2/2] RISC-V: KVM: Redirect illegal instruction traps to guest

On Sat, Jan 28, 2023 at 1:59 PM Anup Patel <apatel@...tanamicro.com> wrote:
>
> From: Andy Chiu <andy.chiu@...ive.com>
>
> The M-mode redirects an unhandled illegal instruction trap back
> to S-mode. However, KVM running in HS-mode terminates the VS-mode
> software when it receives illegal instruction trap. Instead, KVM
> should redirect the illegal instruction trap back to VS-mode, and
> let VS-mode trap handler decide the next step. This futher allows
> guest kernel to implement on-demand enabling of vector extension
> for a guest user space process upon first-use.
>
> Signed-off-by: Andy Chiu <andy.chiu@...ive.com>
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> Reviewed-by: Andrew Jones <ajones@...tanamicro.com>

Queued this patch for Linux-6.3

Thanks,
Anup

> ---
>  arch/riscv/kvm/vcpu_exit.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c
> index af7c4bc07929..4ea101a73d8b 100644
> --- a/arch/riscv/kvm/vcpu_exit.c
> +++ b/arch/riscv/kvm/vcpu_exit.c
> @@ -182,6 +182,12 @@ int kvm_riscv_vcpu_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
>         ret = -EFAULT;
>         run->exit_reason = KVM_EXIT_UNKNOWN;
>         switch (trap->scause) {
> +       case EXC_INST_ILLEGAL:
> +               if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV) {
> +                       kvm_riscv_vcpu_trap_redirect(vcpu, trap);
> +                       ret = 1;
> +               }
> +               break;
>         case EXC_VIRTUAL_INST_FAULT:
>                 if (vcpu->arch.guest_context.hstatus & HSTATUS_SPV)
>                         ret = kvm_riscv_vcpu_virtual_insn(vcpu, run, trap);
> --
> 2.34.1
>