[PATCH] KVM: arm64: Set a linux errno on SMCCC error in kvm_call_hyp_nvhe()

[Fuad Tabba]

Hi Vincent,

On Wed, 3 Jun 2026 at 12:03, Vincent Donnefort <vdonnefort at google.com> wrote:
>
> If the HVC called in kvm_call_hyp_nvhe() fails with an SMCCC error code,
> we WARN. However, the returned value isn't initialized and the caller
> might get garbage or 0 which is likely to be interpreted as success.
>
> Set a default -EPERM error value, ensuring all callers get the message
> when SMCCC calls fail.
>
> Signed-off-by: Vincent Donnefort <vdonnefort at google.com>
>
> ---
>
> I have encountered this issue while working on a follow-up contribution to the
> hypervisor tracing. In that case it completely crashed the kernel because
> IS_ERR() failed on that res.a1 value.
>
> Now, if it makes that function more robust, I do not believe it is fixing any
> existing bug which is why I haven't added a "Fixes:" tag.
>
> In case we want to stick one, here it is:
>
> Fixes: 054698316d87 ("KVM: arm64: nVHE: Migrate hyp interface to SMCCC")

You are fixing a real bug, even if it's latent; I think you should include it.

>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index a49042bfa801..6b8fd494792c 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1273,13 +1273,14 @@ void kvm_arm_resume_guest(struct kvm *kvm);
>  #define vcpu_has_run_once(vcpu)        (!!READ_ONCE((vcpu)->pid))
>
>  #ifndef __KVM_NVHE_HYPERVISOR__
> -#define kvm_call_hyp_nvhe(f, ...)                                              \
> +#define kvm_call_hyp_nvhe(f, ...)                                      \

nit: This realignment would muddle a git blame on this. Prefer you drop it.

Otherwise,

Reviewed-by: Fuad Tabba <tabba at google.com>

Cheers,
/fuad

>         ({                                                              \
>                 struct arm_smccc_res res;                               \
>                                                                         \
>                 arm_smccc_1_1_hvc(KVM_HOST_SMCCC_FUNC(f),               \
>                                   ##__VA_ARGS__, &res);                 \
> -               WARN_ON(res.a0 != SMCCC_RET_SUCCESS);                   \
> +               if (WARN_ON(res.a0 != SMCCC_RET_SUCCESS))               \
> +                       res.a1 = -EPERM;                                \
>                                                                         \
>                 res.a1;                                                 \
>         })
>
> base-commit: e43ffb69e0438cddd72aaa30898b4dc446f664f8
> --
> 2.54.0.1032.g2f8565e1d1-goog
>