Re: [PATCH v9 0/9] IPI virtualization support for VM

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On 4/19/22 17:31, 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 cleanup code in vmx_refresh_apicv_exec_ctrl(). Prepare for
IPIv status dynamical update along with APICv status change.

Patch 7 move kvm_arch_vcpu_precreate() under kvm->lock protection.
This patch is prepared for IPIv PID-table allocation prior to
the creation of vCPUs.

Patch 8 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 9 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.

I queued it, but I am not going to send it to Linus until I get selftests for KVM_CAP_MAX_VCPU_ID. Selftests are generally _not_ optional for new userspace API.

Please send a patch on top of kvm/queue.

Paolo




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