On 2024-08-13 11:05, Marc Zyngier wrote:
In order to plug the brokenness of our current AT implementation,
we need a SW walker that is going to... err.. walk the S1 tables
and tell us what it finds.
Of course, it builds on top of our S2 walker, and share similar
concepts. The beauty of it is that since it uses kvm_read_guest(),
it is able to bring back pages that have been otherwise evicted.
This is then plugged in the two AT S1 emulation functions as
a "slow path" fallback. I'm not sure it is that slow, but hey.
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
arch/arm64/kvm/at.c | 607 +++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 605 insertions(+), 2 deletions(-)
[...]
+static u64 handle_at_slow(struct kvm_vcpu *vcpu, u32 op, u64 vaddr)
+{
+ bool perm_fail, ur, uw, ux, pr, pw, px;
+ struct s1_walk_result wr = {};
+ struct s1_walk_info wi = {};
+ int ret, idx;
+
+ ret = setup_s1_walk(vcpu, op, &wi, &wr, vaddr);
+ if (ret)
+ goto compute_par;
+
+ if (wr.level == S1_MMU_DISABLED)
+ goto compute_par;
+
+ idx = srcu_read_lock(&vcpu->kvm->srcu);
+
+ ret = walk_s1(vcpu, &wi, &wr, vaddr);
+
+ srcu_read_unlock(&vcpu->kvm->srcu, idx);
+
+ if (ret)
+ goto compute_par;
+
+ /* FIXME: revisit when adding indirect permission support */
+ /* AArch64.S1DirectBasePermissions() */
+ if (wi.regime != TR_EL2) {
+ switch (FIELD_GET(PTE_USER | PTE_RDONLY, wr.desc)) {
+ case 0b00:
+ pr = pw = true;
+ ur = uw = false;
+ break;
+ case 0b01:
+ pr = pw = ur = uw = true;
+ break;
+ case 0b10:
+ pr = true;
+ pw = ur = uw = false;
+ break;
+ case 0b11:
+ pr = ur = true;
+ pw = uw = false;
+ break;
+ }
+
+ switch (wr.APTable) {
+ case 0b00:
+ break;
+ case 0b01:
+ ur = uw = false;
+ break;
+ case 0b10:
+ pw = uw = false;
+ break;
+ case 0b11:
+ pw = ur = uw = false;
+ break;
+ }
+
+ /* We don't use px for anything yet, but hey... */
+ px = !((wr.desc & PTE_PXN) || wr.PXNTable || pw);
Annoying (but so far harmless) bug here: the last term should be 'uw',
and not 'pw'. It is a *userspace* writable permission that disables
privileged execution. 'pw' would only make sense if with WXN, and
that has nothing to do with AT at all.
I've fixed that locally.
M.
--
Jazz is not dead. It just smells funny...
