This is an RFC series trying to fix the issue of unnecessary NUMA protection and TLB-shootdowns found in VMs with assigned devices or VFIO mediated devices during NUMA balance. For VMs with assigned devices or VFIO mediated devices, all or part of guest memory are pinned for long-term. Auto NUMA balancing will periodically selects VMAs of a process and change protections to PROT_NONE even though some or all pages in the selected ranges are long-term pinned for DMAs, which is true for VMs with assigned devices or VFIO mediated devices. Though this will not cause real problem because NUMA migration will ultimately reject migration of those kind of pages and restore those PROT_NONE PTEs, it causes KVM's secondary MMU to be zapped periodically with equal SPTEs finally faulted back, wasting CPU cycles and generating unnecessary TLB-shootdowns. This series first introduces a new flag MMU_NOTIFIER_RANGE_NUMA in patch 1 to work with mmu notifier event type MMU_NOTIFY_PROTECTION_VMA, so that the subscriber (e.g.KVM) of the mmu notifier can know that an invalidation event is sent for NUMA migration purpose in specific. Patch 2 skips setting PROT_NONE to long-term pinned pages in the primary MMU to avoid NUMA protection introduced page faults and restoration of old huge PMDs/PTEs in primary MMU. Patch 3 introduces a new mmu notifier callback .numa_protect(), which will be called in patch 4 when a page is ensured to be PROT_NONE protected. Then in patch 5, KVM can recognize a .invalidate_range_start() notification is for NUMA balancing specific and do not do the page unmap in secondary MMU until .numa_protect() comes. Changelog: RFC v1 --> v2: 1. added patch 3-4 to introduce a new callback .numa_protect() 2. Rather than have KVM duplicate logic to check if a page is pinned for long-term, let KVM depend on the new callback .numa_protect() to do the page unmap in secondary MMU for NUMA migration purpose. RFC v1: https://lore.kernel.org/all/20230808071329.19995-1-yan.y.zhao@xxxxxxxxx/ Yan Zhao (5): mm/mmu_notifier: introduce a new mmu notifier flag MMU_NOTIFIER_RANGE_NUMA mm: don't set PROT_NONE to maybe-dma-pinned pages for NUMA-migrate purpose mm/mmu_notifier: introduce a new callback .numa_protect mm/autonuma: call .numa_protect() when page is protected for NUMA migrate KVM: Unmap pages only when it's indeed protected for NUMA migration include/linux/mmu_notifier.h | 16 ++++++++++++++++ mm/huge_memory.c | 6 ++++++ mm/mmu_notifier.c | 18 ++++++++++++++++++ mm/mprotect.c | 10 +++++++++- virt/kvm/kvm_main.c | 25 ++++++++++++++++++++++--- 5 files changed, 71 insertions(+), 4 deletions(-) -- 2.17.1
