On Sat, Apr 26, 2025 at 01:28:11PM +0100, Marc Zyngier wrote:
> We generally don't expect FEAT_LS64* instructions to trap, unless
> they are trapped by a guest hypervisor.
>
> Otherwise, this is just the guest playing tricks on us by using
> an instruction that isn't advertised, which we handle with a well
> deserved UNDEF.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Reviewed-by: Joey Gouly <joey.gouly@xxxxxxx>
> ---
> arch/arm64/kvm/handle_exit.c | 56 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 56 insertions(+)
>
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index b73dc26bc44b4..636c14ed2bb82 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -298,6 +298,61 @@ static int handle_svc(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> +static int handle_other(struct kvm_vcpu *vcpu)
> +{
> + bool is_l2 = vcpu_has_nv(vcpu) && !is_hyp_ctxt(vcpu);
> + u64 hcrx = __vcpu_sys_reg(vcpu, HCRX_EL2);
> + u64 esr = kvm_vcpu_get_esr(vcpu);
> + u64 iss = ESR_ELx_ISS(esr);
> + struct kvm *kvm = vcpu->kvm;
> + bool allowed, fwd = false;
> +
> + /*
> + * We only trap for two reasons:
> + *
> + * - the feature is disabled, and the only outcome is to
> + * generate an UNDEF.
> + *
> + * - the feature is enabled, but a NV guest wants to trap the
> + * feature used my its L2 guest. We forward the exception in
> + * this case.
> + *
> + * What we don't expect is to end-up here if the guest is
> + * expected be be able to directly use the feature, hence the
> + * WARN_ON below.
> + */
> + switch (iss) {
> + case ESR_ELx_ISS_OTHER_ST64BV:
> + allowed = kvm_has_feat(kvm, ID_AA64ISAR1_EL1, LS64, LS64_V);
> + if (is_l2)
> + fwd = !(hcrx & HCRX_EL2_EnASR);
> + break;
> + case ESR_ELx_ISS_OTHER_ST64BV0:
> + allowed = kvm_has_feat(kvm, ID_AA64ISAR1_EL1, LS64, LS64_ACCDATA);
> + if (is_l2)
> + fwd = !(hcrx & HCRX_EL2_EnAS0);
> + break;
> + case ESR_ELx_ISS_OTHER_LDST64B:
> + allowed = kvm_has_feat(kvm, ID_AA64ISAR1_EL1, LS64, LS64);
> + if (is_l2)
> + fwd = !(hcrx & HCRX_EL2_EnALS);
> + break;
> + default:
> + /* Clearly, we're missing something. */
> + WARN_ON_ONCE(1);
> + allowed = false;
> + }
> +
> + WARN_ON_ONCE(allowed && !fwd);
> +
> + if (allowed && fwd)
> + kvm_inject_nested_sync(vcpu, esr);
> + else
> + kvm_inject_undefined(vcpu);
> +
> + return 1;
> +}
> +
> static exit_handle_fn arm_exit_handlers[] = {
> [0 ... ESR_ELx_EC_MAX] = kvm_handle_unknown_ec,
> [ESR_ELx_EC_WFx] = kvm_handle_wfx,
> @@ -307,6 +362,7 @@ static exit_handle_fn arm_exit_handlers[] = {
> [ESR_ELx_EC_CP14_LS] = kvm_handle_cp14_load_store,
> [ESR_ELx_EC_CP10_ID] = kvm_handle_cp10_id,
> [ESR_ELx_EC_CP14_64] = kvm_handle_cp14_64,
> + [ESR_ELx_EC_OTHER] = handle_other,
> [ESR_ELx_EC_HVC32] = handle_hvc,
> [ESR_ELx_EC_SMC32] = handle_smc,
> [ESR_ELx_EC_HVC64] = handle_hvc,
> --
> 2.39.2
>
