Re: [PATCH v19 07/14] KVM: arm64: Forward GCS exceptions to nested guests

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] `kvm_handle_gcs` uses `vcpu_has_nv(vcpu)` instead of `is_nested_ctxt(vcpu)` to forward GCS exceptions, bypassing safety warnings and misrouting unexpected L1 traps.
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--- Patch [7]: [PATCH v19 07/14] KVM: arm64: Forward GCS exceptions to nested guests ---
commit f418917369df0c1bc3138d818288366ea3e842e1
Author: Mark Brown <[email protected]>

KVM: arm64: Forward GCS exceptions to nested guests

This commit adds handling to forward GCS exceptions to nested guests when
HFGITR_EL2.nGCSSTR_EL1 is clear or for GCS data check exceptions in an L2
guest.

> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 54aedf93c78b6..63dcc4a0e69a8 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
[ ... ]
> +/*
> + * We might get GCS exceptions that need to be forwarded to the
> + * hypervisor when a nested guest has HFGITR_EL2.nGCSSTR_EL1 clear, or
> + * for a GCS data check exception for a L2 guest.
> + */
>  static int kvm_handle_gcs(struct kvm_vcpu *vcpu)
>  {
> -	/* We don't expect GCS, so treat it with contempt */
> -	if (kvm_has_feat(vcpu->kvm, ID_AA64PFR1_EL1, GCS, IMP))
> -		WARN_ON_ONCE(1);
> +	if (!kvm_has_gcs(vcpu->kvm)) {
> +		kvm_inject_undefined(vcpu);
> +		return 1;
> +	}
>  
> +	if (vcpu_has_nv(vcpu)) {

[Severity: Medium]
Does this code use the correct check for nested execution here?

By checking vcpu_has_nv() instead of is_nested_ctxt(), if an unexpected GCS
trap occurs while executing the L1 guest, KVM will erroneously forward the
trap to the L1 virtual EL2.

Should this check be is_nested_ctxt(vcpu) so that unexpected L1 traps fall
through to the host WARN_ON_ONCE and correctly inject an UNDEF?

> +		kvm_inject_nested_sync(vcpu, kvm_vcpu_get_esr(vcpu));
> +		return 1;
> +	}
> +
> +	WARN_ON_ONCE(1);
>  	kvm_inject_undefined(vcpu);
>  	return 1;
>  }

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Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=7