[PATCH v4 27/38] KVM: arm64: Return -EFAULT from VCPU_RUN on access to a poisoned pte

Will Deacon
2026-03-27T14:02:19Z

If a protected vCPU faults on an IPA which appears to be mapped, query
the hypervisor to determine whether or not the faulting pte has been
poisoned by a forceful reclaim. If the pte has been poisoned, return
-EFAULT back to userspace rather than retrying the instruction forever.

Tested-by: Fuad Tabba <tabba@google.com>
Tested-by: Mostafa Saleh <smostafa@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/kvm_asm.h | 1 +
arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 +
arch/arm64/kvm/hyp/nvhe/hyp-main.c | 10 +++++
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 43 +++++++++++++++++++
arch/arm64/kvm/pkvm.c | 9 ++--
5 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 04a230e906a7..6c79f7504d80 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -90,6 +90,7 @@ enum __kvm_host_smccc_func {
__KVM_HOST_SMCCC_FUNC___pkvm_unreserve_vm,
__KVM_HOST_SMCCC_FUNC___pkvm_init_vm,
__KVM_HOST_SMCCC_FUNC___pkvm_init_vcpu,
+ __KVM_HOST_SMCCC_FUNC___pkvm_vcpu_in_poison_fault,
__KVM_HOST_SMCCC_FUNC___pkvm_force_reclaim_guest_page,
__KVM_HOST_SMCCC_FUNC___pkvm_reclaim_dying_guest_page,
__KVM_HOST_SMCCC_FUNC___pkvm_start_teardown_vm,
diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index acc031103600..8bc9a2489298 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -40,6 +40,7 @@ int __pkvm_hyp_donate_host(u64 pfn, u64 nr_pages);
int __pkvm_host_share_ffa(u64 pfn, u64 nr_pages);
int __pkvm_host_unshare_ffa(u64 pfn, u64 nr_pages);
int __pkvm_host_donate_guest(u64 pfn, u64 gfn, struct pkvm_hyp_vcpu *vcpu);
+int __pkvm_vcpu_in_poison_fault(struct pkvm_hyp_vcpu *hyp_vcpu);
int __pkvm_host_force_reclaim_page_guest(phys_addr_t phys);
int __pkvm_host_reclaim_page_guest(u64 gfn, struct pkvm_hyp_vm *vm);
int __pkvm_host_share_guest(u64 pfn, u64 gfn, u64 nr_pages, struct pkvm_hyp_vcpu *vcpu,
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 456c83207717..90e3b14fe287 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -573,6 +573,15 @@ static void handle___pkvm_init_vcpu(struct kvm_cpu_context *host_ctxt)
cpu_reg(host_ctxt, 1) = __pkvm_init_vcpu(handle, host_vcpu, vcpu_hva);
}

+static void handle___pkvm_vcpu_in_poison_fault(struct kvm_cpu_context *host_ctxt)
+{
+ int ret;
+ struct pkvm_hyp_vcpu *hyp_vcpu = pkvm_get_loaded_hyp_vcpu();
+
+ ret = hyp_vcpu ? __pkvm_vcpu_in_poison_fault(hyp_vcpu) : -EINVAL;
+ cpu_reg(host_ctxt, 1) = ret;
+}
+
static void handle___pkvm_force_reclaim_guest_page(struct kvm_cpu_context *host_ctxt)
{
DECLARE_REG(phys_addr_t, phys, host_ctxt, 1);
@@ -641,6 +650,7 @@ static const hcall_t host_hcall[] = {
HANDLE_FUNC(__pkvm_unreserve_vm),
HANDLE_FUNC(__pkvm_init_vm),
HANDLE_FUNC(__pkvm_init_vcpu),
+ HANDLE_FUNC(__pkvm_vcpu_in_poison_fault),
HANDLE_FUNC(__pkvm_force_reclaim_guest_page),
HANDLE_FUNC(__pkvm_reclaim_dying_guest_page),
HANDLE_FUNC(__pkvm_start_teardown_vm),
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index dfc512d3bb20..6fc2c77a6920 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -890,6 +890,49 @@ static int get_valid_guest_pte(struct pkvm_hyp_vm *vm, u64 ipa, kvm_pte_t *ptep,
return 0;
}

+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;
+ }
+
+ /*
+ * The host has the faulting IPA when it calls us from the guest
+ * fault handler but we retrieve it ourselves from the FAR so as
+ * to avoid exposing an "oracle" that could reveal data access
+ * patterns of the guest after initial donation of its pages.
+ */
+ ipa = kvm_vcpu_get_fault_ipa(&hyp_vcpu->vcpu);
+ ipa |= FAR_TO_FIPA_OFFSET(kvm_vcpu_get_hfar(&hyp_vcpu->vcpu));
+
+ 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 32294bd21dde..da0a45dab203 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);
+ return ret ? -EFAULT : -EAGAIN;
+ }

ret = kvm_call_hyp_nvhe(__pkvm_host_donate_guest, pfn, gfn);
} else {
--
2.53.0.1018.g2bb0e51243-goog