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

Paolo Bonzini
2022-05-02T16:18:55Z

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