This series enables KVM to save memory when using the TDP MMU by waiting to allocate memslot rmaps until they are needed. To do this, KVM tracks whether or not a shadow root has been allocated. In order to get away with not allocating the rmaps, KVM must also be sure to skip operations which iterate over the rmaps. If the TDP MMU is in use and we have not allocated a shadow root, these operations would essentially be op-ops anyway. Skipping the rmap operations has a secondary benefit of avoiding acquiring the MMU lock in write mode in many cases, substantially reducing MMU lock contention. This series was tested on an Intel Skylake machine. With the TDP MMU off and on, this introduced no new failures on kvm-unit-tests or KVM selftests. Changelog: v2: Incorporated feedback from Paolo and Sean Replaced the memslot_assignment_lock with slots_arch_lock, which has a larger critical section. v3: Removed shadow_mmu_active as suggested by Sean Removed everything except adding a return value to kvm_mmu_init_tdp_mmu from patch 1 of v2 Added RCU protection and better memory ordering for installing the memslot rmaps as suggested by Paolo Reordered most of the patches v4: Renamed functions to allocate and free memslots based on feedback from David. Eliminated the goto in memslot_rmap_alloc, as David suggested. Eliminated kvm_memslots_have_rmaps and updated comments on uses of memslots_have_rmaps. Suggested by Paolo. Changed the description on patch 7 to one Paolo suggested. Collected Reviewed-by tags from David. Dropped the patch to add RCU notations to rmap accesses. v5: Responding to comments from Sean. Improved comments Swapped args to kvm_copy_memslots to match memcpy Fixed some line wrap and declaration style issues No longer check if memslots have rmaps before operations which iterate through active_mmu_pages Re-added the kvm_memslots_have_rmaps helper Fixed a couple missing unlocks for the slots_arch_lock Ben Gardon (7): KVM: x86/mmu: Deduplicate rmap freeing KVM: x86/mmu: Factor out allocating memslot rmap KVM: mmu: Refactor memslot copy KVM: mmu: Add slots_arch_lock for memslot arch fields KVM: x86/mmu: Add a field to control memslot rmap allocation KVM: x86/mmu: Skip rmap operations if rmaps not allocated KVM: x86/mmu: Lazily allocate memslot rmaps arch/x86/include/asm/kvm_host.h | 8 ++ arch/x86/kvm/mmu.h | 10 +++ arch/x86/kvm/mmu/mmu.c | 125 ++++++++++++++++++++------------ arch/x86/kvm/mmu/tdp_mmu.c | 6 +- arch/x86/kvm/mmu/tdp_mmu.h | 4 +- arch/x86/kvm/x86.c | 109 +++++++++++++++++++++++----- include/linux/kvm_host.h | 9 +++ virt/kvm/kvm_main.c | 77 ++++++++++++++++---- 8 files changed, 263 insertions(+), 85 deletions(-) -- 2.31.1.751.gd2f1c929bd-goog
