[PATCH v2 3/3] KVM: arm64: Perform memory fault exits when stage-2 handler EFAULTs

[Anish Moorthy <amoorthy@google.com>]

Right now userspace just gets a bare EFAULT when the stage-2 fault
handler fails to fault in the relevant page. Set up a
KVM_EXIT_MEMORY_FAULT whenever this happens, which at the very least
eases debugging and might also let userspace decide on/take some
specific action other than crashing the VM.

In some cases, user_mem_abort() EFAULTs before the size of the fault is
calculated: return 0 in these cases to indicate that the fault is of
unknown size.

Signed-off-by: Anish Moorthy <amoorthy@google.com>
---
 Documentation/virt/kvm/api.rst |  2 +-
 arch/arm64/kvm/arm.c           |  1 +
 arch/arm64/kvm/mmu.c           | 11 ++++++++++-
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index c5ce7944005c..7b321fefcb3e 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8129,7 +8129,7 @@ unavailable to host or other VMs.
 7.34 KVM_CAP_MEMORY_FAULT_INFO
 ------------------------------
 
-:Architectures: x86
+:Architectures: arm64, x86
 :Returns: Informational only, -EINVAL on direct KVM_ENABLE_CAP.
 
 The presence of this capability indicates that KVM_RUN *may* fill
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index a7ca776b51ec..4121b5a43b9c 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -335,6 +335,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_ARM_SYSTEM_SUSPEND:
 	case KVM_CAP_IRQFD_RESAMPLE:
 	case KVM_CAP_COUNTER_OFFSET:
+	case KVM_CAP_MEMORY_FAULT_INFO:
 		r = 1;
 		break;
 	case KVM_CAP_SET_GUEST_DEBUG2:
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 6981b1bc0946..c97199d1feac 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1448,6 +1448,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 
 	if (fault_is_perm && !write_fault && !exec_fault) {
 		kvm_err("Unexpected L2 read permission error\n");
+		kvm_prepare_memory_fault_exit(vcpu, fault_ipa, 0,
+					      write_fault, exec_fault, false);
 		return -EFAULT;
 	}
 
@@ -1473,6 +1475,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	if (unlikely(!vma)) {
 		kvm_err("Failed to find VMA for hva 0x%lx\n", hva);
 		mmap_read_unlock(current->mm);
+		kvm_prepare_memory_fault_exit(vcpu, fault_ipa, 0,
+					      write_fault, exec_fault, false);
 		return -EFAULT;
 	}
 
@@ -1568,8 +1572,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		kvm_send_hwpoison_signal(hva, vma_shift);
 		return 0;
 	}
-	if (is_error_noslot_pfn(pfn))
+	if (is_error_noslot_pfn(pfn)) {
+		kvm_prepare_memory_fault_exit(vcpu, fault_ipa, vma_pagesize,
+					      write_fault, exec_fault, false);
 		return -EFAULT;
+	}
 
 	if (kvm_is_device_pfn(pfn)) {
 		/*
@@ -1643,6 +1650,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		if (mte_allowed) {
 			sanitise_mte_tags(kvm, pfn, vma_pagesize);
 		} else {
+			kvm_prepare_memory_fault_exit(vcpu, fault_ipa, vma_pagesize,
+						      write_fault, exec_fault, false);
 			ret = -EFAULT;
 			goto out_unlock;
 		}
-- 
2.46.0.76.ge559c4bf1a-goog