[PATCH v5 0/6] KVM: arm64: Improve efficiency of stage2 page table

[Yanan Wang]

Hi,

This series makes some efficiency improvement of guest stage-2 page
table code, and there are some test results to quantify the benefit.
The code has been re-arranged based on the latest kvmarm/next tree.

Descriptions:
We currently uniformly permorm CMOs of D-cache and I-cache in function
user_mem_abort before calling the fault handlers. If we get concurrent
guest faults(e.g. translation faults, permission faults) or some really
unnecessary guest faults caused by BBM, CMOs for the first vcpu are
necessary while the others later are not.

By moving CMOs to the fault handlers, we can easily identify conditions
where they are really needed and avoid the unnecessary ones. As it's a
time consuming process to perform CMOs especially when flushing a block
range, so this solution reduces much load of kvm and improve efficiency
of the stage-2 page table code.

In this series, patch #1, #3, #4 make preparation for place movement
of CMOs (adapt to the latest stage-2 page table framework). And patch
#2, #5 move CMOs of D-cache and I-cache to the fault handlers. Patch
#6 introduces a new way to distinguish cases of memcache allocations.

The following are results in v3 to represent the benefit introduced
by movement of CMOs, and they were tested by [1] (kvm/selftest) that
I have posted recently.
[1] https://lore.kernel.org/lkml/20210302125751.19080-1-wangyanan55@huawei.com/

When there are muitiple vcpus concurrently accessing the same memory
region, we can test the execution time of KVM creating new mappings,
updating the permissions of old mappings from RO to RW, and the time
of re-creating the blocks after they have been split.

hardware platform: HiSilicon Kunpeng920 Server
host kernel: Linux mainline v5.12-rc2

cmdline: ./kvm_page_table_test -m 4 -s anonymous -b 1G -v 80
           (80 vcpus, 1G memory, page mappings(normal 4K))
KVM_CREATE_MAPPINGS: before 104.35s -> after  90.42s  +13.35%
KVM_UPDATE_MAPPINGS: before  78.64s -> after  75.45s  + 4.06%

cmdline: ./kvm_page_table_test -m 4 -s anonymous_thp -b 20G -v 40
           (40 vcpus, 20G memory, block mappings(THP 2M))
KVM_CREATE_MAPPINGS: before  15.66s -> after   6.92s  +55.80%
KVM_UPDATE_MAPPINGS: before 178.80s -> after 123.35s  +31.00%
KVM_REBUILD_BLOCKS:  before 187.34s -> after 131.76s  +30.65%

cmdline: ./kvm_page_table_test -m 4 -s anonymous_hugetlb_1gb -b 20G -v 40
           (40 vcpus, 20G memory, block mappings(HUGETLB 1G))
KVM_CREATE_MAPPINGS: before 104.54s -> after   3.70s  +96.46%
KVM_UPDATE_MAPPINGS: before 174.20s -> after 115.94s  +33.44%
KVM_REBUILD_BLOCKS:  before 103.95s -> after   2.96s  +97.15%

---

Changelogs:
v4->v5:
- rebased on the latest kvmarm/tree to adapt to the new stage-2 page-table code
- v4: https://lore.kernel.org/lkml/20210409033652.28316-1-wangyanan55@huawei.com/

v3->v4:
- perform D-cache flush if we are not mapping device memory
- rebased on top of mainline v5.12-rc6
- v3: https://lore.kernel.org/lkml/20210326031654.3716-1-wangyanan55@huawei.com/

v2->v3:
- drop patch #3 in v2
- retest v3 based on v5.12-rc2
- v2: https://lore.kernel.org/lkml/20210310094319.18760-1-wangyanan55@huawei.com/

v1->v2:
- rebased on top of mainline v5.12-rc2
- also move CMOs of I-cache to the fault handlers
- retest v2 based on v5.12-rc2
- v1: https://lore.kernel.org/lkml/20210208112250.163568-1-wangyanan55@huawei.com/

---

Yanan Wang (6):
  KVM: arm64: Introduce KVM_PGTABLE_S2_GUEST stage-2 flag
  KVM: arm64: Move D-cache flush to the fault handlers
  KVM: arm64: Add mm_ops member for structure stage2_attr_data
  KVM: arm64: Provide invalidate_icache_range at non-VHE EL2
  KVM: arm64: Move I-cache flush to the fault handlers
  KVM: arm64: Distinguish cases of memcache allocations completely

 arch/arm64/include/asm/kvm_mmu.h     | 31 -------------
 arch/arm64/include/asm/kvm_pgtable.h | 38 ++++++++++------
 arch/arm64/kvm/hyp/nvhe/cache.S      | 11 +++++
 arch/arm64/kvm/hyp/pgtable.c         | 65 +++++++++++++++++++++++-----
 arch/arm64/kvm/mmu.c                 | 51 ++++++++--------------
 5 files changed, 107 insertions(+), 89 deletions(-)

-- 
2.23.0