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

Marc Zyngier
2024-10-24T14:21:52Z

On Thu, 24 Oct 2024 14:59:25 +0100,
Joey Gouly <joey.gouly@arm.com> wrote:
>
> 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.

True. Maybe I should drop them all apart from the one in
setup_s1_walk().

>
> > +
> > + 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.

The reason for doing so was not to give the impression that we were
actively using the unprivileged indirect permissions for TR_EL2.

But maybe that's be just as clear with a comment.

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

Thanks!

M.

--
Without deviation from the norm, progress is not possible.