[RFC,v5,11/38] KVM: arm64: Print a warning for unexpected faults on locked memslots

Commit Message

Alexandru Elisei Nov. 17, 2021, 3:38 p.m. UTC

When userspace unmaps a VMA backing a memslot, the corresponding stage 2
address range gets unmapped via the MMU notifiers. This makes it possible
to get stage 2 faults on a locked memslot, which might not be what
userspace wants because the purpose of locking a memslot is to avoid stage
2 faults in the first place.

Addresses being unmapped from stage 2 can happen from other reasons too,
like bugs in the implementation of the lock memslot API, however unlikely
that might seem (or not).

Let's try to make debugging easier by printing a warning when this happens.

Signed-off-by: Alexandru Elisei <[e-mail]>
---
 arch/arm64/kvm/mmu.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

Patch

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index bc2a546f65c3..3e9ec646cc34 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1352,6 +1352,27 @@  int kvm_handle_guest_abort(struct kvm_vcpu *vcpu)
 	/* Userspace should not be able to register out-of-bounds IPAs */
 	VM_BUG_ON(fault_ipa >= kvm_phys_size(vcpu->kvm));
 
+	if (memslot_is_locked(memslot)) {
+		const char *fault_type_str;
+
+		if (kvm_vcpu_trap_is_exec_fault(vcpu))
+			goto handle_fault;
+
+		if (fault_status == FSC_ACCESS)
+			fault_type_str = "access";
+		else if (write_fault && (memslot->arch.flags & KVM_MEMSLOT_LOCK_WRITE))
+			fault_type_str = "write";
+		else if (!write_fault)
+			fault_type_str = "read";
+		else
+			goto handle_fault;
+
+		kvm_warn_ratelimited("Unexpected L2 %s fault on locked memslot %d: IPA=%#llx, ESR_EL2=%#08x]\n",
+				     fault_type_str, memslot->id, fault_ipa,
+				     kvm_vcpu_get_esr(vcpu));
+	}
+
+handle_fault:
 	if (fault_status == FSC_ACCESS) {
 		handle_access_fault(vcpu, fault_ipa);
 		ret = 1;