[PATCH v4 00/12] KVM: x86/mmu: refine memtype related mmu zap

From: Yan Zhao
Date: Fri Jul 14 2023 - 03:14:44 EST

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This series refines mmu zap caused by EPT memory type update when guest
MTRRs are honored.

Patches 1-5 revolve around utilizing helper functions to check if
KVM TDP honors guest MTRRs, TDP zaps and page fault max_level reduction
are now only targeted to TDPs that honor guest MTRRs.

-The 5th patch will trigger zapping of TDP leaf entries if non-coherent
DMA devices count goes from 0 to 1 or from 1 to 0.

Patches 6-7 are fixes and patches 9-12 are optimizations for mmu zaps
when guest MTRRs are honored.
Those mmu zaps are intended to remove stale memtypes of TDP entries
caused by changes of guest MTRRs and CR0.CD and are usually triggered from
all vCPUs in bursts.

- The 6th patch places TDP zap to when CR0.CD toggles and when guest MTRRs
update under CR0.CD=0.

- The 7th-8th patches refine KVM_X86_QUIRK_CD_NW_CLEARED by removing the
IPAT bit in EPT memtype when CR0.CD=1 and guest MTRRs are honored.

- The 9th-11th patches are optimizations of the mmu zap when guest MTRRs
are honored by serializing vCPUs' gfn zap requests and calculating of
precise fine-grained ranges to zap.
They are put in mtrr.c because the optimizations are related to when
guest MTRRs are honored and because it requires to read guest MTRRs
for fine-grained ranges.
Calls to kvm_unmap_gfn_range() are not included into the optimization,
because they are not triggered from all vCPUs in bursts and not all of
them are blockable. They usually happen at memslot removal and thus do
not affect the mmu zaps when guest MTRRs are honored. Also, current
performance data shows that there's no observable performance difference
to mmu zaps by turning on/off auto numa balancing triggered
kvm_unmap_gfn_range().

- The 12th patch further convert kvm_zap_gfn_range() to use shared
mmu_lock in TDP MMU. It can visibly help to reduce cost in contentions
along with vCPUs number increases.

A reference performance data for last 7 patches as below:

Base1: base code before patch 6
Base2: Base 1 + patches 6 + 7 + 8
patch 6: move TDP zaps from guest MTRRs update to CR0.CD toggling
patch 7: drop IPAT in memtype when CD=1 for
KVM_X86_QUIRK_CD_NW_CLEARED
patch 8: entralize code to get CD=1 memtype when guest MTRRs are
honored

patch 9: serialize gfn zap
patch 10: fine-grained gfn zap
patch 11: split and zap in-slot gfn ranges only **
patch 12: convert gfn zap to use shared mmu_lock
_________________________________________________________________________
guest bios: OVMF | 8 vCPUs memory=16G | 16 vCPUs memory=16G |
CPU frequency: 3100 MHz | zap cycles | zap cnt | zap cycles | zap cnt |
---------------------------|----------------------|----------------------|
Base1 | 3506.37M | 84 | 17683.24M | 164 |
Base2 | 4241.46M | 74 | 25944.80M | 146 |*
Base2 + Patch 9 | 319.23M | 74 | 6183.92M | 146 |
Base2 + Patches 9+10 | 128.34M | 74 | 1735.13M | 146 |
Base2 + Patches 9+10+11 | 37.17M | 74 | 357.68M | 146 |
Base2 + Patches 9+10+11+12 | 17.21M | 74 | 39.85M | 146 |
---------------------------|----------------------|----------------------|
Base2 + Patch 12 | 32.66M | 74 | 74.77M | 146 |
Base2 + Patches 9+10+12 | 15.01M | 74 | 35.46M | 146 |
___________________________|______________________|______________________|

_________________________________________________________________________
guest bios: Seabios | 8 vCPUs memory=16G | 16 vCPUs memory=16G |
CPU frequency: 3100 MHz | zap cycles | zap cnt | zap cycles | zap cnt |
---------------------------|----------------------|----------------------|
Base1 | 44.55M | 50 | 532.71M | 98 |
Base2 | 526.65M | 42 | 2138.80M | 82 |*
Base2 + Patch 9 | 116.59M | 42 | 922.68M | 82 |
Base2 + Patches 9+10 | 62.09M | 42 | 377.15M | 82 |
Base2 + Patches 9+10+11 | 17.86M | 42 | 49.88M | 82 |
Base2 + Patches 9+10+11+12 | 16.98M | 42 | 44.64M | 82 |
---------------------------|----------------------|----------------------|
Base2 + Patch 12 | 24.65M | 42 | 62.04M | 82 |
Base2 + Patches 9+10+12 | 18.44M | 42 | 41.88M | 82 |
___________________________|______________________|______________________|

* With Base2, EPT zap cnt are reduced because there are some MTRR updates
under CR0.CD=1.
EPT zap cycles increases a bit (especially true in case of Seabios)
because concurrency is more intense when CR0.CD toggles than when
guest MTRRs update.
(patch 7/8 are neglectable in performance)

** patch 11 splits a single gfn range that may cover out-of-slot ranges
into several in-slot ranges and zap only those in-slot ranges.
It essentially reduces the counts to check contentions and yileds
when mmu_lock is held for write.
However, if mmu_lock is held for read (i.e. with patch 12), the
effect of reducing contention and yileds from patch 11 are not that
obvious, whereas patch 11 may introduce more kmalloc() for splitting.
So, I intend to drop patch 11 if patch 12 is acceptable.

Changelog:
v3 --> v4:
1. Added patch 12 of converting gfn zap to use shared mmu_lock.
2. Updated commit messages of patch 3 and patch 4 to better describe
patch intention. (Sean)
3. Updated commit message of patch 7 to explain the problem better.
(Chao Gao, Xiaoyao Li, Yuan Yao)
4. Renamed kvm_mtrr_get_cd_memory_type() to
kvm_honors_guest_mtrrs_get_cd_memtype() in patch 8.
5. Renamed kvm_zap_gfn_range_on_cd_toggle() to
kvm_honors_guest_mtrrs_get_cd_memtype() in patch 9.
6. Move initialization of mtrr_zap_list_lock and mtrr_zap_list from
kvm_vcpu_mtrr_init() to kvm_arch_init_vm(). (Sean)
7. Removed unnecesary kvm_clear_mtrr_zap_list() in patch 9 and moved it
to patch 10. (Yuan Yao).
8. Added a table in comment for fine-grained zapping for
kvm_honors_guest_mtrrs_zap_on_cd_toggle(). (Yuan Yao)

v2 --> v3:
1. Updated patch 1 about definition of honor guest MTRRs helper. (Sean)
2. Added patch 2 to use honor guest MTRRs helper in kvm_tdp_page_fault().
(Sean)
3. Remove unnecessary calculation of MTRR ranges.
(Chao Gao, Kai Huang, Sean)
4. Updated patches 3-5 to use the helper. (Chao Gao, Kai Huang, Sean)
5. Added patches 6,7 to reposition TDP zap and drop IPAT bit. (Sean)
6. Added patch 8 to prepare for patch 10's memtype calculation when
CR0.CD=1.
7. Added patches 9-11 to speed up MTRR update /CD0 toggle when guest
MTRRs are honored. (Sean)
8. Dropped per-VM based MTRRs in v2 (Sean)

v1 --> v2:
1. Added a helper to skip non EPT case in patch 1
2. Added patch 2 to skip mmu zap when guest CR0_CD changes if EPT is not
enabled. (Chao Gao)
3. Added patch 3 to skip mmu zap when guest MTRR changes if EPT is not
enabled.
4. Do not mention TDX in patch 4 as the code is not merged yet (Chao Gao)
5. Added patches 5-6 to reduce EPT zap during guest bootup.

v3:
https://lore.kernel.org/all/20230616023101.7019-1-yan.y.zhao@xxxxxxxxx/

v2:
https://lore.kernel.org/all/20230509134825.1523-1-yan.y.zhao@xxxxxxxxx/

v1:
https://lore.kernel.org/all/20230508034700.7686-1-yan.y.zhao@xxxxxxxxx/

Yan Zhao (12):
KVM: x86/mmu: helpers to return if KVM honors guest MTRRs
KVM: x86/mmu: Use KVM honors guest MTRRs helper in
kvm_tdp_page_fault()
KVM: x86/mmu: Use KVM honors guest MTRRs helper when CR0.CD toggles
KVM: x86/mmu: Use KVM honors guest MTRRs helper when update mtrr
KVM: x86/mmu: zap KVM TDP when noncoherent DMA assignment starts/stops
KVM: x86/mmu: move TDP zaps from guest MTRRs update to CR0.CD toggling
KVM: VMX: drop IPAT in memtype when CD=1 for
KVM_X86_QUIRK_CD_NW_CLEARED
KVM: x86: centralize code to get CD=1 memtype when guest MTRRs are
honored
KVM: x86/mmu: serialize vCPUs to zap gfn when guest MTRRs are honored
KVM: x86/mmu: fine-grained gfn zap when guest MTRRs are honored
KVM: x86/mmu: split a single gfn zap range when guest MTRRs are
honored
KVM: x86/mmu: convert kvm_zap_gfn_range() to use shared mmu_lock in
TDP MMU

arch/x86/include/asm/kvm_host.h | 4 +
arch/x86/kvm/mmu.h | 7 +
arch/x86/kvm/mmu/mmu.c | 32 +++-
arch/x86/kvm/mmu/tdp_mmu.c | 50 +++++
arch/x86/kvm/mmu/tdp_mmu.h | 1 +
arch/x86/kvm/mtrr.c | 328 +++++++++++++++++++++++++++++++-
arch/x86/kvm/vmx/vmx.c | 11 +-
arch/x86/kvm/x86.c | 28 ++-
arch/x86/kvm/x86.h | 3 +
9 files changed, 439 insertions(+), 25 deletions(-)

--
2.17.1

Next message: William Qiu: "Re: [PATCH v2 2/3] dt-bindings: spi: constrain minItems of clocks and clock-names"
Previous message: huzhi001: "[PATCH] VFS: Fix seven errors in bitmap.c"
Next in thread: Yan Zhao: "[PATCH v4 01/12] KVM: x86/mmu: helpers to return if KVM honors guest MTRRs"
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