On Thu, Nov 17, 2022 at 6:01 PM Robert Hoo <robert.hu@xxxxxxxxxxxxxxx> wrote: > > On Thu, 2022-11-17 at 10:43 -0800, David Matlack wrote: > > On Thu, Nov 17, 2022 at 8:14 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> > > wrote: > > > if (is_shadow_present_pte(iter.old_spte)) > > > - ret = tdp_mmu_split_huge_page(kvm, &iter, > > > sp, true); > > > + r = tdp_mmu_split_huge_page(kvm, &iter, sp, > > > true); > > > else > > > - ret = tdp_mmu_link_sp(kvm, &iter, sp, > > > true); > > > + r = tdp_mmu_link_sp(kvm, &iter, sp, true); > > > > Can this fix be squashed into [1]? It seems like a serious enough > > bug. > > If 2 threads race to update the same PTE, KVM will return -EBUSY out > > to userspace from KVM_RUN, I think. I'm not sure about QEMU, but that > > would be fatal for the VM in Vanadium. > > > > [1] > > https://lore.kernel.org/kvm/20221109185905.486172-3-dmatlack@xxxxxxxxxx/ > > > I think in you patch it's all right, since then before > kvm_tdp_mmu_map() returns, it must go through > tdp_mmu_map_handle_target_level(), it returns RET_PF_* enum. Ah that's right. kvm_tdp_mmu_map() won't actually return 0/-EBUSY, because it either returns RET_PF_RETRY or goes through tdp_mmu_map_handle_target_level().
