This patch series implements a new dirty logging mode utilizing the Dirty
bits in the SPTEs, when available, instead of relying on write protection.
On hosts that do not support PML, this can result in significant
improvement in VM performance for some workloads during the brownout phase
of a live migration when compared to write protection based dirty logging,
because of the elimination of all the VM exits on memory writes.
However, this new mode does incur additional time in the get_dirty_log
IOCTL because of having to scan all the SPTEs for dirtiness, which can
in some cases, result in slightly elongating the blackout time. Two
strategies can be used to mitigate that. The first, included in this
series, is to have the ability to dynamically switch between D Bit based
and write protection based dirty logging modes. Then the mode could be
switched to write protection just before entering blackout, thus incurring
less time in the get_dirty_log IOCTL during blackout, while keeping the
reduced overhead of the D Bit based mode during brownout. Secondly, the
scan in the get_dirty_log IOCTL can be parallelized, which results in that
IOCTL becoming faster for all modes. That patch series will be sent out
separately a little later.
The series also includes a couple of other minor dirty logging related
performance improvements, including removal of extra TLB flushes in one
instance and more efficient functions for testing/clearing Writable/Dirty
bits.
Junaid Shahid (10):
kvm: mmu: spte_write_protect optimization
kvm: mmu: Allow reading hardware dirty state from
kvm_get_dirty_log_protect
kvm: x86: mmu: Change __rmap_clear_dirty to
__rmap_test_and_clear_dirty
kvm: mmu: x86: Add dirty bit clearing notification hook
kvm: x86: mmu: Remove extra TLB flush from vmx_slot_enable_log_dirty()
kvm: x86: mmu: Use D bit for dirty logging
kvm: x86: mmu: Per-VM dirty logging mode
kvm: x86: mmu: Refactor kvm_mmu_slot_*_remove_write_access
kvm: x86: mmu: Ability to switch dirty logging mode dynamically
kvm: x86: mmu: Add IOCTLs to allow userspace to switch dirty logging
mode
Documentation/virtual/kvm/api.txt | 39 +++
arch/mips/kvm/mmu.c | 16 +-
arch/x86/include/asm/kvm_host.h | 27 ++-
arch/x86/include/uapi/asm/kvm.h | 5 +
arch/x86/kvm/mmu.c | 390 +++++++++++++++++++++++++-----
arch/x86/kvm/mmu.h | 3 +
arch/x86/kvm/vmx.c | 20 +-
arch/x86/kvm/x86.c | 54 ++++-
include/linux/kvm_host.h | 8 +-
include/uapi/linux/kvm.h | 3 +
virt/kvm/arm/mmu.c | 9 +-
virt/kvm/kvm_main.c | 21 +-
12 files changed, 482 insertions(+), 113 deletions(-)
--
2.19.1.568.g152ad8e336-goog
