On 3/4/2022 4:07 PM, Zeng, Guang wrote:
Currently, issuing an IPI except self-ipi in guest on Intel CPU always causes a VM-exit. It can lead to non-negligible overhead to some workloads involving frequent IPIs when running in VMs. IPI virtualization is a new VT-x feature, targeting to eliminate VM-exits on source vCPUs when issuing unicast, physical-addressing IPIs. Once it is enabled, the processor virtualizes following kinds of operations that send IPIs without causing VM-exits: - Memory-mapped ICR writes - MSR-mapped ICR writes - SENDUIPI execution This patch series implements IPI virtualization support in KVM. Patches 1-4 add tertiary processor-based VM-execution support framework, which is used to enumerate IPI virtualization. Patch 5 handles APIC-write VM exit due to writes to ICR MSR when guest works in x2APIC mode. This is a new case introduced by Intel VT-x. Patch 6 disallow the APIC ID change unconditionally. Patch 7 provide userspace capability to set maximum possible VCPU ID for current VM. IPIv can refer to this value to allocate memory for PID-pointer table. Patch 8 implements IPI virtualization related function including feature enabling through tertiary processor-based VM-execution in various scenarios of VMCS configuration, PID table setup in vCPU creation and vCPU block consideration. Document for IPI virtualization is now available at the latest "Intel Architecture Instruction Set Extensions Programming Reference". Document Link: https://software.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html We did experiment to measure average time sending IPI from source vCPU to the target vCPU completing the IPI handling by kvm unittest w/ and w/o IPI virtualization. When IPI virtualization enabled, it will reduce 22.21% and 15.98% cycles consuming in xAPIC mode and x2APIC mode respectively. -------------------------------------- KVM unittest:vmexit/ipi 2 vCPU, AP was modified to run in idle loop instead of halt to ensure no VM exit impact on target vCPU. Cycles of IPI xAPIC mode x2APIC mode test w/o IPIv w/ IPIv w/o IPIv w/ IPIv 1 6106 4816 4265 3768 2 6244 4656 4404 3546 3 6165 4658 4233 3474 4 5992 4710 4363 3430 5 6083 4741 4215 3551 6 6238 4904 4304 3547 7 6164 4617 4263 3709 8 5984 4763 4518 3779 9 5931 4712 4645 3667 10 5955 4530 4332 3724 11 5897 4673 4283 3569 12 6140 4794 4178 3598 13 6183 4728 4363 3628 14 5991 4994 4509 3842 15 5866 4665 4520 3739 16 6032 4654 4229 3701 17 6050 4653 4185 3726 18 6004 4792 4319 3746 19 5961 4626 4196 3392 20 6194 4576 4433 3760 Average cycles 6059 4713.1 4337.85 3644.8 %Reduction -22.21% -15.98% -------------------------------------- IPI microbenchmark: (https://lore.kernel.org/kvm/20171219085010.4081-1-ynorov@xxxxxxxxxxxxxxxxxx) 2 vCPUs, 1:1 pin vCPU to pCPU, guest VM runs with idle=poll, x2APIC mode Result with IPIv enabled: Dry-run: 0, 272798 ns Self-IPI: 5094123, 11114037 ns Normal IPI: 131697087, 173321200 ns Broadcast IPI: 0, 155649075 ns Broadcast lock: 0, 161518031 ns Result with IPIv disabled: Dry-run: 0, 272766 ns Self-IPI: 5091788, 11123699 ns Normal IPI: 145215772, 174558920 ns Broadcast IPI: 0, 175785384 ns Broadcast lock: 0, 149076195 ns As IPIv can benefit unicast IPI to other CPU, Normal IPI test case gain about 9.73% time saving on average out of 15 test runs when IPIv is enabled. Normal IPI statistics (unit:ns): test w/o IPIv w/ IPIv 1 153346049 140907046 2 147218648 141660618 3 145215772 117890672 4 146621682 136430470 5 144821472 136199421 6 144704378 131676928 7 141403224 131697087 8 144775766 125476250 9 140658192 137263330 10 144768626 138593127 11 145166679 131946752 12 145020451 116852889 13 148161353 131406280 14 148378655 130174353 15 148903652 127969674 Average time 145944306.6 131742993.1 ns %Reduction -9.73% -------------------------------------- hackbench: 8 vCPUs, guest VM free run, x2APIC mode ./hackbench -p -l 100000 w/o IPIv w/ IPIv Time 91.887 74.605 %Reduction -18.808% 96 vCPUs, guest VM free run, x2APIC mode ./hackbench -p -l 1000000 w/o IPIv w/ IPIv Time 287.504 235.185 %Reduction -18.198% -------------------------------------- v6->v7: 1. Revise kvm_apic_write_nodecode() on dealing with vICR busy bit in x2apic mode 2. Merge PID-table memory allocation with max_vcpu_id into IPIv enabling patch 3. Change to allocate PID-table, setup vCPU's PID-table entry and IPIv related VMCS fields once IPIv can be enabled, which support runtime enabling IPIv. v5->v6: 1. Adapt kvm_apic_write_nodecode() implementation based on Sean's fix of x2apic's ICR register process. 2. Drop the patch handling IPIv table entry setting in case APIC ID changed, instead applying Levitsky's patch to disallow setting APIC ID in any case. 3. Drop the patch resizing the PID-pointer table on demand. Allow userspace to set maximum vcpu id at runtime that IPIv can refer to the practical value to allocate memory for PID-pointer table. v4 -> v5: 1. Deal with enable_ipiv parameter following current vmcs configuration rule. 2. Allocate memory for PID-pointer table dynamically 3. Support guest runtime modify APIC ID in xAPIC mode 4. Helper to judge possibility to take PI block in IPIv case v3 -> v4: 1. Refine code style of patch 2 2. Move tertiary control shadow build into patch 3 3. Make vmx_tertiary_exec_control to be static function v2 -> v3: 1. Misc change on tertiary execution control definition and capability setup 2. Alternative to get tertiary execution control configuration v1 -> v2: 1. Refine the IPIv enabling logic for VM. Remove ipiv_active definition per vCPU. -------------------------------------- Chao Gao (1): KVM: VMX: enable IPI virtualization Maxim Levitsky (1): KVM: x86: lapic: don't allow to change APIC ID unconditionally Robert Hoo (4): x86/cpu: Add new VMX feature, Tertiary VM-Execution control KVM: VMX: Extend BUILD_CONTROLS_SHADOW macro to support 64-bit variation KVM: VMX: Detect Tertiary VM-Execution control when setup VMCS config KVM: VMX: dump_vmcs() reports tertiary_exec_control field as well Zeng Guang (2): KVM: x86: Add support for vICR APIC-write VM-Exits in x2APIC mode KVM: x86: Allow userspace set maximum VCPU id for VM arch/x86/include/asm/kvm_host.h | 6 ++ arch/x86/include/asm/msr-index.h | 1 + arch/x86/include/asm/vmx.h | 11 +++ arch/x86/include/asm/vmxfeatures.h | 5 +- arch/x86/kernel/cpu/feat_ctl.c | 9 +- arch/x86/kvm/lapic.c | 47 ++++++++-- arch/x86/kvm/vmx/capabilities.h | 13 +++ arch/x86/kvm/vmx/evmcs.c | 2 + arch/x86/kvm/vmx/evmcs.h | 1 + arch/x86/kvm/vmx/posted_intr.c | 15 ++- arch/x86/kvm/vmx/vmcs.h | 1 + arch/x86/kvm/vmx/vmx.c | 141 +++++++++++++++++++++++++++-- arch/x86/kvm/vmx/vmx.h | 65 +++++++------ arch/x86/kvm/x86.c | 11 +++ 14 files changed, 280 insertions(+), 48 deletions(-)
Kindly ping ! :)
