Re: [PATCH v13 20/35] KVM: x86/mmu: Handle page fault for private memory

[Paolo Bonzini]

On Sun, Nov 5, 2023 at 2:04 PM Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx> wrote:
>
> > +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

Paolo