[PATCH v3 2/5] KVM: arm64: GICv3: Completely disable trapping on vcpu exit

[Fuad Tabba]

Hi Marc,

On Mon, 17 Nov 2025 at 09:20, Marc Zyngier <maz at kernel.org> wrote:
>
> Fuad reports that on QEMU, the DIR trapping is still effective after
> a vcpu exit and that the host is running nVHE, resulting in a BUG()
> (we only expect DIR to be trapped for the guest, and never the host).
>
> As it turns out, this is an implementation-dependent behaviour, which
> the architecture allows, but that seem to be relatively uncommon across
> implementations.
>
> Fix this by completely zeroing the ICH_HCR_EL2 register when the
> vcpu exits.
>
> Reported-by: Fuad Tabba <tabba at google.com>

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

Cheers,
/fuad

> Fixes: ca30799f7c2d0 ("KVM: arm64: Turn vgic-v3 errata traps into a patched-in constant")
> Closes: https://lore.kernel.org/r/CA+EHjTzRwswNq+hZQDD5tXj+-0nr04OmR201mHmi82FJ0VHuJA@mail.gmail.com
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/hyp/vgic-v3-sr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/hyp/vgic-v3-sr.c b/arch/arm64/kvm/hyp/vgic-v3-sr.c
> index e950efa225478..71199e1a92940 100644
> --- a/arch/arm64/kvm/hyp/vgic-v3-sr.c
> +++ b/arch/arm64/kvm/hyp/vgic-v3-sr.c
> @@ -243,7 +243,7 @@ void __vgic_v3_save_state(struct vgic_v3_cpu_if *cpu_if)
>                 cpu_if->vgic_hcr |= val & ICH_HCR_EL2_EOIcount;
>         }
>
> -       write_gicreg(compute_ich_hcr(cpu_if) & ~ICH_HCR_EL2_En, ICH_HCR_EL2);
> +       write_gicreg(0, ICH_HCR_EL2);
>  }
>
>  void __vgic_v3_restore_state(struct vgic_v3_cpu_if *cpu_if)
> --
> 2.47.3
>
>