[PATCH 00/10] arm/arm64: KVM: limit icache invalidation to prefetch aborts

[Marc Zyngier]

It was recently reported that on a VM restore, we seem to spend a
disproportionate amount of time invalidation the icache. This is
partially due to some HW behaviour, but also because we're being a bit
dumb and are invalidating the icache for every page we map at S2, even
if that on a data access.

The slightly better way of doing this is to mark the pages XN at S2,
and wait for the the guest to execute something in that page, at which
point we perform the invalidation. As it is likely that there is a lot
less instruction than data, we win (or so we hope).

We also take this opportunity to drop the extra dcache clean to the
PoU which is pretty useless, as we already clean all the way to the
PoC...

Running a bare metal test that touches 1GB of memory (using a 4kB
stride) leads to the following results on Seattle:

4.13:
do_fault_read.bin:       0.565885992 seconds time elapsed
do_fault_write.bin:       0.738296337 seconds time elapsed
do_fault_read_write.bin:       1.241812231 seconds time elapsed

4.14-rc3+patches:
do_fault_read.bin:       0.244961803 seconds time elapsed
do_fault_write.bin:       0.422740092 seconds time elapsed
do_fault_read_write.bin:       0.643402470 seconds time elapsed

We're almost halving the time of something that more or less looks
like a restore operation. Some larger systems will show much bigger
benefits as they become less impacted by the icache invalidation
(which is broadcast in the inner shareable domain).

I've also given it a test run on both Cubietruck and Jetson-TK1.

Tests are archived here:
https://git.kernel.org/pub/scm/linux/kernel/git/maz/kvm-ws-tests.git/

I'd value some additional test results on HW I don't have access to.

Thanks,

	M.

Marc Zyngier (10):
  KVM: arm/arm64: Split dcache/icache flushing
  arm64: KVM: Add invalidate_icache_range helper
  arm: KVM: Add optimized PIPT icache flushing
  arm64: KVM: PTE/PMD S2 XN bit definition
  KVM: arm/arm64: Limit icache invalidation to prefetch aborts
  KVM: arm/arm64: Only clean the dcache on translation fault
  KVM: arm/arm64: Preserve Exec permission across R/W permission faults
  KVM: arm/arm64: Drop vcpu parameter from
    coherent_{d,i}cache_guest_page
  KVM: arm/arm64: Detangle kvm_mmu.h from kvm_hyp.h
  arm: KVM: Use common implementation for all flushes to PoC

 arch/arm/include/asm/kvm_hyp.h         |   3 +-
 arch/arm/include/asm/kvm_mmu.h         | 110 +++++++++++++++++++++++----------
 arch/arm/include/asm/pgtable.h         |   4 +-
 arch/arm/kvm/hyp/switch.c              |   1 +
 arch/arm/kvm/hyp/tlb.c                 |   1 +
 arch/arm64/include/asm/cacheflush.h    |   8 +++
 arch/arm64/include/asm/kvm_hyp.h       |   1 -
 arch/arm64/include/asm/kvm_mmu.h       |  37 +++++++++--
 arch/arm64/include/asm/pgtable-hwdef.h |   2 +
 arch/arm64/include/asm/pgtable-prot.h  |   4 +-
 arch/arm64/kvm/hyp/debug-sr.c          |   1 +
 arch/arm64/kvm/hyp/switch.c            |   1 +
 arch/arm64/kvm/hyp/tlb.c               |   1 +
 arch/arm64/mm/cache.S                  |  24 +++++++
 virt/kvm/arm/hyp/vgic-v2-sr.c          |   1 +
 virt/kvm/arm/mmu.c                     |  68 +++++++++++++++++---
 16 files changed, 213 insertions(+), 54 deletions(-)

-- 
2.14.1