On Mon, Dec 12, 2022, David Matlack wrote: > On Mon, Dec 12, 2022 at 11:32 AM Ben Gardon <bgardon@xxxxxxxxxx> wrote: > > > > On Thu, Dec 8, 2022 at 11:39 AM David Matlack <dmatlack@xxxxxxxxxx> wrote: > > > > > > Abstract away kvm_mmu_max_mapping_level(), which is an x86-specific > > > function for computing the max level that a given GFN can be mapped in > > > KVM's page tables. This will be used in a future commit to enable moving > > > the TDP MMU to common code. > > > > > > Provide a default implementation for non-x86 architectures that just > > > returns the max level. This will result in more zapping than necessary > > > when disabling dirty logging (i.e. less than optimal performance) but no > > > correctness issues. > > > > Apologies if you already implemented it in a later patch in this > > series, but would it not at least be possible to port > > host_pfn_mapping_level to common code and check that? > > I'm assuming, though I could be wrong, that all archs map GFNs with at > > most a host page table granularity mapping. > > I suppose that doesn't strictly need to be included in this series, > > but it would be worth addressing in the commit description. > > It's not implemented later in this series, but I agree it's something > we should do. In fact, it's worth doing regardless of this series as a > way to share more code across architectures (e.g. KVM/ARM has it's own > version in arch/arm64/kvm/mmu.c:get_user_mapping_size()). Ya, ARM converted to walking the host user page tables largely in response to x86's conversion. After x86 switched, ARM was left holding the bag that was PageTransCompoundMap(). On a related topic, I'm guessing all the comments in transparent_hugepage_adjust() about the code working _only_ for THP are stale. Unless ARM support for HugeTLB works differently, walking host user page tables should Just Work for all hugepage types.
