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From: Alistair Francis <alistair23@gmail.com>
To: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Cc: qemu-devel@nongnu.org, qemu-riscv@nongnu.org,
	alistair.francis@wdc.com,  bmeng@tinylab.org,
	liwei1518@gmail.com, zhiwei_liu@linux.alibaba.com,
	 palmer@rivosinc.com, ajones@ventanamicro.com
Subject: Re: [PATCH v2 1/1] target/riscv/kvm: tolerate KVM disable ext errors
Date: Mon, 29 Apr 2024 12:57:40 +1000	[thread overview]
Message-ID: <CAKmqyKOAx-DuEe3dP9T8GcWt_Vm4RLLJFOZm8FXzRqKm1DwE-A@mail.gmail.com> (raw)
In-Reply-To: <20240422171425.333037-2-dbarboza@ventanamicro.com>

On Tue, Apr 23, 2024 at 3:15 AM Daniel Henrique Barboza
<dbarboza@ventanamicro.com> wrote:
>
> Running a KVM guest using a 6.9-rc3 kernel, in a 6.8 host that has zkr
> enabled, will fail with a kernel oops SIGILL right at the start. The
> reason is that we can't expose zkr without implementing the SEED CSR.
> Disabling zkr in the guest would be a workaround, but if the KVM doesn't
> allow it we'll error out and never boot.
>
> In hindsight this is too strict. If we keep proceeding, despite not
> disabling the extension in the KVM vcpu, we'll not add the extension in
> the riscv,isa. The guest kernel will be unaware of the extension, i.e.
> it doesn't matter if the KVM vcpu has it enabled underneath or not. So
> it's ok to keep booting in this case.
>
> Change our current logic to not error out if we fail to disable an
> extension in kvm_set_one_reg(), but show a warning and keep booting. It
> is important to throw a warning because we must make the user aware that
> the extension is still available in the vcpu, meaning that an
> ill-behaved guest can ignore the riscv,isa settings and  use the
> extension.
>
> The case we're handling happens with an EINVAL error code. If we fail to
> disable the extension in KVM for any other reason, error out.
>
> We'll also keep erroring out when we fail to enable an extension in KVM,
> since adding the extension in riscv,isa at this point will cause a guest
> malfunction because the extension isn't enabled in the vcpu.
>
> Suggested-by: Andrew Jones <ajones@ventanamicro.com>
> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>

Thanks!

Applied to riscv-to-apply.next

Alistair

> ---
>  target/riscv/kvm/kvm-cpu.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index 6a6c6cae80..03e3fee607 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -427,10 +427,14 @@ static void kvm_riscv_update_cpu_cfg_isa_ext(RISCVCPU *cpu, CPUState *cs)
>          reg = kvm_cpu_cfg_get(cpu, multi_ext_cfg);
>          ret = kvm_set_one_reg(cs, id, &reg);
>          if (ret != 0) {
> -            error_report("Unable to %s extension %s in KVM, error %d",
> -                         reg ? "enable" : "disable",
> -                         multi_ext_cfg->name, ret);
> -            exit(EXIT_FAILURE);
> +            if (!reg && ret == -EINVAL) {
> +                warn_report("KVM cannot disable extension %s",
> +                            multi_ext_cfg->name);
> +            } else {
> +                error_report("Unable to enable extension %s in KVM, error %d",
> +                             multi_ext_cfg->name, ret);
> +                exit(EXIT_FAILURE);
> +            }
>          }
>      }
>  }
> --
> 2.44.0
>
>

     prev parent reply	other threads:[~2024-04-29  2:58 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-22 17:14 [PATCH v2 0/1] target/riscv/kvm: tolerate KVM disable ext errors Daniel Henrique Barboza
2024-04-22 17:14 ` [PATCH v2 1/1] " Daniel Henrique Barboza
2024-04-25 15:58   ` Andrew Jones
2024-04-29  2:57   ` Alistair Francis [this message]

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