Hi Marc,
On Mon, 10 Feb 2025 at 18:42, Marc Zyngier <maz@xxxxxxxxxx> 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>
> ---
> arch/arm64/kvm/handle_exit.c | 64 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 64 insertions(+)
>
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 512d152233ff2..4f8354bf7dc5f 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -294,6 +294,69 @@ static int handle_svc(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> +static int handle_ls64b(struct kvm_vcpu *vcpu)
> +{
> + struct kvm *kvm = vcpu->kvm;
> + u64 esr = kvm_vcpu_get_esr(vcpu);
> + u64 iss = ESR_ELx_ISS(esr);
> + bool allowed;
> +
> + switch (iss) {
> + case ESR_ELx_ISS_ST64BV:
> + allowed = kvm_has_feat(kvm, ID_AA64ISAR1_EL1, LS64, LS64_V);
> + break;
> + case ESR_ELx_ISS_ST64BV0:
> + allowed = kvm_has_feat(kvm, ID_AA64ISAR1_EL1, LS64, LS64_ACCDATA);
> + break;
> + case ESR_ELx_ISS_LDST64B:
> + allowed = kvm_has_feat(kvm, ID_AA64ISAR1_EL1, LS64, LS64);
> + break;
> + default:
> + /* Clearly, we're missing something. */
> + goto unknown_trap;
> + }
> +
> + if (!allowed)
> + goto undef;
> +
> + if (vcpu_has_nv(vcpu) && !is_hyp_ctxt(vcpu)) {
> + u64 hcrx = __vcpu_sys_reg(vcpu, HCRX_EL2);
> + bool fwd;
> +
> + switch (iss) {
> + case ESR_ELx_ISS_ST64BV:
> + fwd = !(hcrx & HCRX_EL2_EnASR);
> + break;
> + case ESR_ELx_ISS_ST64BV0:
> + fwd = !(hcrx & HCRX_EL2_EnAS0);
> + break;
> + case ESR_ELx_ISS_LDST64B:
> + fwd = !(hcrx & HCRX_EL2_EnALS);
> + break;
> + default:
> + /* We don't expect to be here */
> + fwd = false;
> + }
> +
> + if (fwd) {
> + kvm_inject_nested_sync(vcpu, esr);
> + return 1;
> + }
> + }
> +
> +unknown_trap:
> + /*
> + * If we land here, something must be very wrong, because we
> + * have no idea why we trapped at all. Warn and undef as a
> + * fallback.
> + */
> + WARN_ON(1);
nit: should this be WARN_ONCE() instead?
> +
> +undef:
> + kvm_inject_undefined(vcpu);
> + return 1;
> +}
I'm wondering if this can be simplified by having one switch()
statement that toggles both allowed and fwd (or maybe even only fwd),
and then inject depending on that, e.g.,
+static int handle_ls64b(struct kvm_vcpu *vcpu)
+{
+ struct kvm *kvm = vcpu->kvm;
+ bool is_nv = 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);
+ bool fwd = false;
+
+ switch (iss) {
+ case ESR_ELx_ISS_ST64BV:
+ fwd = kvm_has_feat(kvm, ID_AA64ISAR1_EL1, LS64, LS64_V) &&
+ !(hcrx & HCRX_EL2_EnASR)
+ break;
...
+ default:
+ WARN_ONCE(1);
+ }
+
+ if (is_nv && fwd) {
+ kvm_inject_nested_sync(vcpu, esr);
+ else
+ kvm_inject_undefined(vcpu);
+
+ return 1;
+}
I think this has the same effect as the code above.
Cheers,
/fuad
> +
> static exit_handle_fn arm_exit_handlers[] = {
> [0 ... ESR_ELx_EC_MAX] = kvm_handle_unknown_ec,
> [ESR_ELx_EC_WFx] = kvm_handle_wfx,
> @@ -303,6 +366,7 @@ 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_LS64B] = handle_ls64b,
> [ESR_ELx_EC_HVC32] = handle_hvc,
> [ESR_ELx_EC_SMC32] = handle_smc,
> [ESR_ELx_EC_HVC64] = handle_hvc,
> --
> 2.39.2
>
