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Message-ID: <2d33b71a-13e5-d377-abc2-c20958526497@redhat.com>
Date:   Mon, 2 May 2022 18:18:39 +0200
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To:     Zeng Guang <guang.zeng@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Kim Phillips <kim.phillips@amd.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Jethro Beekman <jethro@fortanix.com>,
        Kai Huang <kai.huang@intel.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org,
        Robert Hu <robert.hu@intel.com>, Gao Chao <chao.gao@intel.com>
References: <20220419153155.11504-1-guang.zeng@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v9 0/9] IPI virtualization support for VM
In-Reply-To: <20220419153155.11504-1-guang.zeng@intel.com>
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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