On Tue, Nov 30, 2021, David Matlack wrote: > > I have a similar patch for the old MMU, but it was also replacing > > shadow_root_level with shadow_root_role. I'll see if I can adapt it to > > the TDP MMU, since the shadow_root_role is obviously the same for both. > > While I was writing this patch it got me wondering if we can do an > even more general refactor and replace root_hpa and shadow_root_level > with a pointer to the root kvm_mmu_page struct. But I didn't get a > chance to look into it further. For TDP MUU, yes, as root_hpa == __pa(sp->spt) in all cases. For the legacy/full MMU, not without additional refactoring since root_hpa doesn't point at a kvm_mmu_page when KVM shadows a non-paging guest with PAE paging (uses pae_root), or when KVM shadows nested NPT and the guest is using fewer paging levels that the host (uses pml5_root or pml4_root). if (mmu->shadow_root_level == PT64_ROOT_5LEVEL) mmu->root_hpa = __pa(mmu->pml5_root); else if (mmu->shadow_root_level == PT64_ROOT_4LEVEL) mmu->root_hpa = __pa(mmu->pml4_root); else mmu->root_hpa = __pa(mmu->pae_root); That's definitely a solvable problem, e.g. it wouldn't be a problem to burn a few kvm_mmu_page for the special root. The biggest issue is probably the sheer amount of code that would need to be updated. I do think it would be a good change, but I think we'd want to do it in a release that isn't expected to have many other MMU changes. shadow_root_level can also be replaced by mmu_role.base.level. I've never bothered to do the replacement because there's zero memory savings and it would undoubtedly take me some time to retrain my brain :-)
