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Patch series "userfaultfd: working set tracking for VM guest memory", v10. This series adds userfaultfd support for tracking the working set of VM guest memory, so a VMM can identify hot pages and reclaim cold ones to tiered or remote storage. This patch (of 15): pte_protnone() and pmd_protnone() detect present-but-inaccessible page table entries. This capability is useful beyond NUMA balancing -- for example, userfaultfd working set tracking uses protnone PTEs to track page access without unmapping pages. Introduce CONFIG_ARCH_HAS_PTE_PROTNONE to decouple the protnone PTE infrastructure from CONFIG_NUMA_BALANCING. The six architectures that support protnone PTEs (x86_64, arm64, powerpc, s390, riscv, loongarch) now select this option, and CONFIG_NUMA_BALANCING depends on it. No functional change -- the same set of architectures continues to have working protnone support, but the infrastructure is now available independently of NUMA balancing. Link: https://lore.kernel.org/20260708111417.173443-1-kirill@shutemov.name Link: https://lore.kernel.org/20260708111417.173443-2-kirill@shutemov.name Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org> Assisted-by: Claude:claude-opus-4-6 Acked-by: SeongJae Park <sj@kernel.org> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Hildenbrand <david@kernel.org> Cc: James Houghton <jthoughton@google.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Liam Howlett <liam@infradead.org> Cc: Lorenzo Stoakes <ljs@kernel.org> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Peter Xu <peterx@redhat.com> Cc: Sean Christopherson <seanjc@google.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Vlastimil Babka <vbabka@kernel.org> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>