[PATCH 14/20] KVM: arm64: Simplify handling of HCR_EL2.E2H RESx

[Fuad Tabba]

Hi Marc,

On Mon, 26 Jan 2026 at 12:17, Marc Zyngier <maz at kernel.org> wrote:
>
> Now that we can link the RESx behaviour with the value of HCR_EL2.E2H,
> we can trivially express the tautological constraint that makes E2H
> a reserved value at all times.
>
> Fun, isn't it?
>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/config.c | 13 ++-----------
>  1 file changed, 2 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm64/kvm/config.c b/arch/arm64/kvm/config.c
> index d5871758f1fcc..187d047a9cf4a 100644
> --- a/arch/arm64/kvm/config.c
> +++ b/arch/arm64/kvm/config.c
> @@ -394,16 +394,6 @@ static bool feat_vmid16(struct kvm *kvm)
>         return kvm_has_feat_enum(kvm, ID_AA64MMFR1_EL1, VMIDBits, 16);
>  }
>
> -static bool compute_hcr_e2h(struct kvm *kvm, struct resx *bits)
> -{
> -       if (kvm_has_feat(kvm, FEAT_E2H0))
> -               bits->res0 |= HCR_EL2_E2H;
> -       else
> -               bits->res1 |= HCR_EL2_E2H;
> -
> -       return true;
> -}
> -
>  static const struct reg_bits_to_feat_map hfgrtr_feat_map[] = {
>         NEEDS_FEAT(HFGRTR_EL2_nAMAIR2_EL1       |
>                    HFGRTR_EL2_nMAIR2_EL1,
> @@ -1023,7 +1013,8 @@ static const struct reg_bits_to_feat_map hcr_feat_map[] = {
>         NEEDS_FEAT(HCR_EL2_TWEDEL       |
>                    HCR_EL2_TWEDEn,
>                    FEAT_TWED),
> -       NEEDS_FEAT_FIXED(HCR_EL2_E2H, compute_hcr_e2h),
> +       NEEDS_FEAT_FLAG(HCR_EL2_E2H, RES0_WHEN_E2H0 | RES1_WHEN_E2H1,
> +                       enforce_resx),

If you were to take my suggestion for the previous patch, I think that
you could express this as follows:

    FORCE_RESx | RES0_WHEN_E2H0 | RES1_WHEN_E2H1

Or if you use the modified patch 12:

    FORCE_RESx | RES1_WHEN_E2H1

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

Cheers,
/fuad

>         FORCE_RES0(HCR_EL2_RES0),
>         FORCE_RES1(HCR_EL2_RES1),
>  };


> --
> 2.47.3
>