On Thu, Oct 13, 2022, David Matlack wrote: > On Wed, Oct 12, 2022 at 11:17 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > I'm not dead set against having a dedicated TDP MMU page fault handler, but > > IMO it's not really better once the TDP MMU vs. shadow MMU is reduced to a > > static branch, just different. The read vs. write mmu_lock is the most > > visible ugliness, and that can be buried in helpers if we really want to > > make the page fault handler easier on the eyes, e.g. ... > My preference is still separate handlers. When I am reading this code, > I only care about one path (TDP MMU or Shadow MMU, usually TDP MMU). > Having separate handlers makes it easy to read since I don't have to > care about the implementation details of the other MMU. > > And more importantly (but less certain), the TDP MMU fault handler is > going to diverge further from the Shadow MMU fault handler in the near > future. i.e. There will be more and more branches in a common fault > handler, and the value of having a common fault handler diminishes. > Specifically, to support moving the TDP MMU to common code, the TDP > MMU is no longer going to topup the same mem caches as the Shadow MMU > (TDP MMU is not going to use struct kvm_mmu_page), and the TDP MMU > will probably have its own fast_page_fault() handler eventually. What if we hold off on the split for the moment, and then revisit the handler when a common MMU is closer to reality? I agree that a separate handler makes sense once things start diverging, but until that happens, supporting two flows instead of one seems like it would add (minor) maintenance cost without much benefit. > If we do go the common handler route, I don't prefer the > direct_page_fault_mmu_lock/unlock() wrapper since it further obscures > the differences between the 2 MMUs. Yeah, I don't like the wrappers either.
