KVM branch: https://github.com/xzpeter/linux/tree/kvm-dirty-ring QEMU branch for testing: https://github.com/xzpeter/qemu/tree/kvm-dirty-ring v5: - rebased to 5.6-rc4 (removed Paolo's r-b in patch 4 for context change) - selftest: run all supported modes if mode not specified [Drew] - selftest: expose vcpu->fd directly to test using vcpu_get_fd [Drew] v4: - refactor ring layout: remove indices, use bit 0/1 in the gfn.flags field to encode GFN status (invalid, dirtied, collected) [Michael, Paolo] - patch memslot_valid_for_gpte() too to check against memslot flags rather than dirty_bitmap pointer - fix build on non-x86 arch [syzbot] - fix comment for kvm_dirty_gfn [Michael] - check against VM_EXEC, VM_SHARED for mmaps [Michael] - fix "KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]" to unbreak unrestricted_guest=N [Sean] - some rework in the test code, e.g., more comments For previous versions, please refer to: V1: https://lore.kernel.org/kvm/20191129213505.18472-1-peterx@xxxxxxxxxx V2: https://lore.kernel.org/kvm/20191221014938.58831-1-peterx@xxxxxxxxxx V3: https://lore.kernel.org/kvm/20200109145729.32898-1-peterx@xxxxxxxxxx V4: https://lore.kernel.org/kvm/20200205025105.367213-1-peterx@xxxxxxxxxx Overview ============ This is a continued work from Lei Cao <lei.cao@xxxxxxxxxxx> and Paolo Bonzini on the KVM dirty ring interface. The new dirty ring interface is another way to collect dirty pages for the virtual machines. It is different from the existing dirty logging interface in a few ways, majorly: - Data format: The dirty data was in a ring format rather than a bitmap format, so dirty bits to sync for dirty logging does not depend on the size of guest memory any more, but speed of dirtying. Also, the dirty ring is per-vcpu, while the dirty bitmap is per-vm. - Data copy: The sync of dirty pages does not need data copy any more, but instead the ring is shared between the userspace and kernel by page sharings (mmap() on vcpu fd) - Interface: Instead of using the old KVM_GET_DIRTY_LOG, KVM_CLEAR_DIRTY_LOG interfaces, the new ring uses the new KVM_RESET_DIRTY_RINGS ioctl when we want to reset the collected dirty pages to protected mode again (works like KVM_CLEAR_DIRTY_LOG, but ring based). To collecting dirty bits, we only need to read the ring data, no ioctl is needed. Ring Layout =========== KVM dirty ring is per-vcpu. Each ring is an array of kvm_dirty_gfn defined as: struct kvm_dirty_gfn { __u32 flags; __u32 slot; /* as_id | slot_id */ __u64 offset; }; Each GFN is a state machine itself. The state is embeded in the flags field, as defined in the uapi header: /* * KVM dirty GFN flags, defined as: * * |---------------+---------------+--------------| * | bit 1 (reset) | bit 0 (dirty) | Status | * |---------------+---------------+--------------| * | 0 | 0 | Invalid GFN | * | 0 | 1 | Dirty GFN | * | 1 | X | GFN to reset | * |---------------+---------------+--------------| * * Lifecycle of a dirty GFN goes like: * * dirtied collected reset * 00 -----------> 01 -------------> 1X -------+ * ^ | * | | * +------------------------------------------+ * * The userspace program is only responsible for the 01->1X state * conversion (to collect dirty bits). Also, it must not skip any * dirty bits so that dirty bits are always collected in sequence. */ Testing ======= This series provided both the implementation of the KVM dirty ring and the test case. Also I've implemented the QEMU counterpart that can run with the new KVM, link can be found at the top of the cover letter. However that's still a very initial version which is prone to change and future optimizations. I did some measurement with the new method with 24G guest running some dirty workload, I don't see any speedup so far, even in some heavy dirty load it'll be slower (e.g., when 800MB/s random dirty rate, kvm dirty ring takes average of ~73s to complete migration while dirty logging only needs average of ~55s). However that's understandable because 24G guest means only 1M dirty bitmap, that's still a suitable case for dirty logging. Meanwhile heavier workload means worst case for dirty ring. More tests are welcomed if there's bigger host/guest, especially on COLO-like workload. Please review, thanks. Peter Xu (14): KVM: X86: Change parameter for fast_page_fault tracepoint KVM: Cache as_id in kvm_memory_slot KVM: X86: Don't track dirty for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR] KVM: Pass in kvm pointer into mark_page_dirty_in_slot() KVM: X86: Implement ring-based dirty memory tracking KVM: Make dirty ring exclusive to dirty bitmap log KVM: Don't allocate dirty bitmap if dirty ring is enabled KVM: selftests: Always clear dirty bitmap after iteration KVM: selftests: Sync uapi/linux/kvm.h to tools/ KVM: selftests: Use a single binary for dirty/clear log test KVM: selftests: Introduce after_vcpu_run hook for dirty log test KVM: selftests: Add dirty ring buffer test KVM: selftests: Let dirty_log_test async for dirty ring test KVM: selftests: Add "-c" parameter to dirty log test Documentation/virt/kvm/api.rst | 123 +++++ arch/x86/include/asm/kvm_host.h | 6 +- arch/x86/include/uapi/asm/kvm.h | 1 + arch/x86/kvm/Makefile | 3 +- arch/x86/kvm/mmu/mmu.c | 10 +- arch/x86/kvm/mmutrace.h | 9 +- arch/x86/kvm/svm.c | 9 +- arch/x86/kvm/vmx/vmx.c | 85 +-- arch/x86/kvm/x86.c | 49 +- include/linux/kvm_dirty_ring.h | 50 ++ include/linux/kvm_host.h | 21 + include/trace/events/kvm.h | 78 +++ include/uapi/linux/kvm.h | 44 ++ tools/include/uapi/linux/kvm.h | 44 ++ tools/testing/selftests/kvm/Makefile | 2 - .../selftests/kvm/clear_dirty_log_test.c | 2 - tools/testing/selftests/kvm/dirty_log_test.c | 488 ++++++++++++++++-- .../testing/selftests/kvm/include/kvm_util.h | 4 + tools/testing/selftests/kvm/lib/kvm_util.c | 67 +++ .../selftests/kvm/lib/kvm_util_internal.h | 4 + virt/kvm/dirty_ring.c | 176 +++++++ virt/kvm/kvm_main.c | 236 ++++++++- 22 files changed, 1386 insertions(+), 125 deletions(-) create mode 100644 include/linux/kvm_dirty_ring.h delete mode 100644 tools/testing/selftests/kvm/clear_dirty_log_test.c create mode 100644 virt/kvm/dirty_ring.c -- 2.24.1
