Re: [PATCH 22/30] KVM: arm64: Return -EFAULT from VCPU_RUN on access to a poisoned pte

Quentin Perret
2026-01-06T15:54:12Z

On Monday 05 Jan 2026 at 15:49:30 (+0000), Will Deacon wrote:
> +int __pkvm_vcpu_in_poison_fault(struct pkvm_hyp_vcpu *hyp_vcpu)
> +{
> + struct pkvm_hyp_vm *vm = pkvm_hyp_vcpu_to_hyp_vm(hyp_vcpu);
> + kvm_pte_t pte;
> + s8 level;
> + u64 ipa;
> + int ret;
> +
> + switch (kvm_vcpu_trap_get_class(&hyp_vcpu->vcpu)) {
> + case ESR_ELx_EC_DABT_LOW:
> + case ESR_ELx_EC_IABT_LOW:
> + if (kvm_vcpu_trap_is_translation_fault(&hyp_vcpu->vcpu))
> + break;
> + fallthrough;
> + default:
> + return -EINVAL;
> + }
> +
> + ipa = kvm_vcpu_get_fault_ipa(&hyp_vcpu->vcpu);
> + ipa |= kvm_vcpu_get_hfar(&hyp_vcpu->vcpu) & GENMASK(11, 0);

Why is all the above needed? Could we simplify by having the host pass
the IPA to the hcall?

> + guest_lock_component(vm);
> + ret = kvm_pgtable_get_leaf(&vm->pgt, ipa, &pte, &level);
> + if (ret)
> + goto unlock;
> +
> + if (level != KVM_PGTABLE_LAST_LEVEL) {
> + ret = -EINVAL;
> + goto unlock;
> + }
> +
> + ret = guest_pte_is_poisoned(pte);
> +unlock:
> + guest_unlock_component(vm);
> + return ret;
> +}
> +
> int __pkvm_host_share_hyp(u64 pfn)
> {
> u64 phys = hyp_pfn_to_phys(pfn);
> diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
> index d1926cb08c76..14865907610c 100644
> --- a/arch/arm64/kvm/pkvm.c
> +++ b/arch/arm64/kvm/pkvm.c
> @@ -417,10 +417,13 @@ int pkvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
> return -EINVAL;
>
> /*
> - * We raced with another vCPU.
> + * We either raced with another vCPU or the guest PTE
> + * has been poisoned by an erroneous host access.
> */
> - if (mapping)
> - return -EAGAIN;
> + if (mapping) {
> + ret = kvm_call_hyp_nvhe(__pkvm_vcpu_in_poison_fault);

It's not too bad, but it's a shame we now issue that every time we have
such a race (which is frequent-ish). Could we perhaps only issue it if
at least one page has been forcefully reclaimed since boot?

> + return ret ? -EFAULT : -EAGAIN;
> + }
>
> ret = kvm_call_hyp_nvhe(__pkvm_host_donate_guest, pfn, gfn);
> } else {
> --
> 2.52.0.351.gbe84eed79e-goog
>