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Subject[RFC V2 0/9] x86/mmu:Introduce parallel memory virtualization to boost performance
Date
From: Yulei Zhang <yulei.kernel@gmail.com>

Currently in KVM memory virtulization we relay on mmu_lock to
synchronize the memory mapping update, which make vCPUs work
in serialize mode and slow down the execution, especially after
migration to do substantial memory mapping will cause visible
performance drop, and it can get worse if guest has more vCPU
numbers and memories.

The idea we present in this patch set is to mitigate the issue
with pre-constructed memory mapping table. We will fast pin the
guest memory to build up a global memory mapping table according
to the guest memslots changes and apply it to cr3, so that after
guest starts up all the vCPUs would be able to update the memory
simultaneously without page fault exception, thus the performance
improvement is expected.

We use memory dirty pattern workload to test the initial patch
set and get positive result even with huge page enabled. For example,
we create guest with 32 vCPUs and 64G memories, and let the vcpus
dirty the entire memory region concurrently, as the initial patch
eliminate the overhead of mmu_lock, in 2M/1G huge page mode we would
get the job done in about 50% faster.

We only validate this feature on Intel x86 platform. And as Ben
pointed out in RFC V1, so far we disable the SMM for resource
consideration, drop the mmu notification as in this case the
memory is pinned.

V1->V2:
* Rebase the code to kernel version 5.9.0-rc1.

Yulei Zhang (9):
Introduce new fields in kvm_arch/vcpu_arch struct for direct build EPT
support
Introduce page table population function for direct build EPT feature
Introduce page table remove function for direct build EPT feature
Add release function for direct build ept when guest VM exit
Modify the page fault path to meet the direct build EPT requirement
Apply the direct build EPT according to the memory slots change
Add migration support when using direct build EPT
Introduce kvm module parameter global_tdp to turn on the direct build
EPT mode
Handle certain mmu exposed functions properly while turn on direct
build EPT mode

arch/mips/kvm/mips.c | 13 +
arch/powerpc/kvm/powerpc.c | 13 +
arch/s390/kvm/kvm-s390.c | 13 +
arch/x86/include/asm/kvm_host.h | 13 +-
arch/x86/kvm/mmu/mmu.c | 533 ++++++++++++++++++++++++++++++--
arch/x86/kvm/svm/svm.c | 2 +-
arch/x86/kvm/vmx/vmx.c | 7 +-
arch/x86/kvm/x86.c | 55 ++--
include/linux/kvm_host.h | 7 +-
virt/kvm/kvm_main.c | 43 ++-
10 files changed, 639 insertions(+), 60 deletions(-)

--
2.17.1

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