On Sun, Nov 05, 2023 at 05:19:36PM +0100, Paolo Bonzini wrote:

On Sun, Nov 5, 2023 at 2:04 PM Xu Yilun [off-list ref] wrote:

quoted

quoted

+static void kvm_mmu_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
+                                           struct kvm_page_fault *fault)
+{
+     kvm_prepare_memory_fault_exit(vcpu, fault->gfn << PAGE_SHIFT,
+                                   PAGE_SIZE, fault->write, fault->exec,
+                                   fault->is_private);
+}
+
+static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
+                                struct kvm_page_fault *fault)
+{
+     int max_order, r;
+
+     if (!kvm_slot_can_be_private(fault->slot)) {
+             kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
+             return -EFAULT;
+     }
+
+     r = kvm_gmem_get_pfn(vcpu->kvm, fault->slot, fault->gfn, &fault->pfn,
+                          &max_order);
+     if (r) {
+             kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
+             return r;

Why report KVM_EXIT_MEMORY_FAULT here? even with a ret != -EFAULT?

The cases are EFAULT, EHWPOISON (which can report
KVM_EXIT_MEMORY_FAULT) and ENOMEM. I think it's fine
that even -ENOMEM can return KVM_EXIT_MEMORY_FAULT,
and it doesn't violate the documentation.  The docs tell you "what
can you do if error if EFAULT or EHWPOISON?"; they don't
exclude that other errnos result in KVM_EXIT_MEMORY_FAULT,
it's just that you're not supposed to look at it

Thanks, it's OK for ENOMEM + KVM_EXIT_MEMORY_FAULT.

Another concern is, now 3 places to report EFAULT + KVM_EXIT_MEMORY_FAULT:

  if (!kvm_slot_can_be_private(fault->slot)) {
	kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
	return -EFAULT;
  }

  file = kvm_gmem_get_file(slot);
  if (!file)
	return -EFAULT;

  if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
	kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
	return -EFAULT;
  }

They are different cases, and seems userspace should handle them
differently, but not enough information to distinguish them.

Thanks,
Yilun

Paolo