Re: [PATCH v5 21/37] KVM: arm64: Implement AT S1PIE support

Joey Gouly
2024-10-24T13:59:29Z

On Wed, Oct 23, 2024 at 03:53:29PM +0100, Marc Zyngier wrote:
> It doesn't take much effort to implement S1PIE support in AT.
>
> It is only a matter of using the AArch64.S1IndirectBasePermissions()
> encodings for the permission, ignoring GCS which has no impact on AT,
> and enforce FEAT_PAN3 being enabled as this is a requirement of
> FEAT_S1PIE.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/at.c | 117 +++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 116 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
> index f5bd750288ff5..3d93ed1795603 100644
> --- a/arch/arm64/kvm/at.c
> +++ b/arch/arm64/kvm/at.c
> @@ -781,6 +781,9 @@ static bool pan3_enabled(struct kvm_vcpu *vcpu, enum trans_regime regime)
> if (!kvm_has_feat(vcpu->kvm, ID_AA64MMFR1_EL1, PAN, PAN3))
> return false;
>
> + if (s1pie_enabled(vcpu, regime))
> + return true;
> +
> if (regime == TR_EL10)
> sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL1);
> else
> @@ -862,11 +865,123 @@ static void compute_s1_hierarchical_permissions(struct kvm_vcpu *vcpu,
> }
> }
>
> +#define perm_idx(v, r, i) ((vcpu_read_sys_reg((v), (r)) >> ((i) * 4)) & 0xf)
> +
> +#define set_priv_perms(wr, r, w, x) \
> + do { \
> + (wr)->pr = (r); \
> + (wr)->pw = (w); \
> + (wr)->px = (x); \
> + } while (0)
> +
> +#define set_unpriv_perms(wr, r, w, x) \
> + do { \
> + (wr)->ur = (r); \
> + (wr)->uw = (w); \
> + (wr)->ux = (x); \
> + } while (0)
> +
> +/* Similar to AArch64.S1IndirectBasePermissions(), without GCS */
> +#define set_perms(w, wr, ip) \
> + do { \
> + /* R_LLZDZ */ \
> + switch ((ip)) { \
> + case 0b0000: \
> + set_ ## w ## _perms((wr), false, false, false); \
> + break; \
> + case 0b0001: \
> + set_ ## w ## _perms((wr), true , false, false); \
> + break; \
> + case 0b0010: \
> + set_ ## w ## _perms((wr), false, false, true ); \
> + break; \
> + case 0b0011: \
> + set_ ## w ## _perms((wr), true , false, true ); \
> + break; \
> + case 0b0100: \
> + set_ ## w ## _perms((wr), false, false, false); \
> + break; \
> + case 0b0101: \
> + set_ ## w ## _perms((wr), true , true , false); \
> + break; \
> + case 0b0110: \
> + set_ ## w ## _perms((wr), true , true , true ); \
> + break; \
> + case 0b0111: \
> + set_ ## w ## _perms((wr), true , true , true ); \
> + break; \
> + case 0b1000: \
> + set_ ## w ## _perms((wr), true , false, false); \
> + break; \
> + case 0b1001: \
> + set_ ## w ## _perms((wr), true , false, false); \
> + break; \
> + case 0b1010: \
> + set_ ## w ## _perms((wr), true , false, true ); \
> + break; \
> + case 0b1011: \
> + set_ ## w ## _perms((wr), false, false, false); \
> + break; \
> + case 0b1100: \
> + set_ ## w ## _perms((wr), true , true , false); \
> + break; \
> + case 0b1101: \
> + set_ ## w ## _perms((wr), false, false, false); \
> + break; \
> + case 0b1110: \
> + set_ ## w ## _perms((wr), true , true , true ); \
> + break; \
> + case 0b1111: \
> + set_ ## w ## _perms((wr), false, false, false); \
> + break; \
> + } \
> + } while (0)
> +
> +static void compute_s1_indirect_permissions(struct kvm_vcpu *vcpu,
> + struct s1_walk_info *wi,
> + struct s1_walk_result *wr)
> +{
> + u8 up, pp, idx;
> +
> + idx = pte_pi_index(wr->desc);
> +
> + switch (wi->regime) {
> + case TR_EL10:
> + pp = perm_idx(vcpu, PIR_EL1, idx);
> + up = perm_idx(vcpu, PIRE0_EL1, idx);
> + break;
> + case TR_EL20:
> + pp = perm_idx(vcpu, PIR_EL2, idx);
> + up = perm_idx(vcpu, PIRE0_EL2, idx);
> + break;
> + case TR_EL2:
> + pp = perm_idx(vcpu, PIR_EL2, idx);
> + up = 0;
> + break;
> + }

There seems to be inconsistent use of

default:
BUG();

when switching on wi->regime.

> +
> + set_perms(priv, wr, pp);
> +
> + if (wi->regime != TR_EL2)
> + set_perms(unpriv, wr, up);
> + else
> + set_unpriv_perms(wr, false, false, false);

When regime == TR_EL2, up == 0, so the if/else should do the same thing? Maybe
you've done that intentionally to be more explicit.

Either way:

Reviewed-by: Joey Gouly <joey.gouly@arm.com>

> +
> + /* R_VFPJF */
> + if (wr->px && wr->uw) {
> + set_priv_perms(wr, false, false, false);
> + set_unpriv_perms(wr, false, false, false);
> + }
> +}
> +
> static void compute_s1_permissions(struct kvm_vcpu *vcpu, u32 op,
> struct s1_walk_info *wi,
> struct s1_walk_result *wr)
> {
> - compute_s1_direct_permissions(vcpu, wi, wr);
> + if (!s1pie_enabled(vcpu, wi->regime))
> + compute_s1_direct_permissions(vcpu, wi, wr);
> + else
> + compute_s1_indirect_permissions(vcpu, wi, wr);
>
> if (!wi->hpd)
> compute_s1_hierarchical_permissions(vcpu, wi, wr);

Thanks,
Joey