Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH 2/2] KVM: X86: Implement PV send IPI support
To:     Wanpeng Li <kernellwp@gmail.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>
References: <1530265876-18136-1-git-send-email-wanpengli@tencent.com>
 <1530265876-18136-3-git-send-email-wanpengli@tencent.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Openpgp: preference=signencrypt
Autocrypt: addr=pbonzini@redhat.com; prefer-encrypt=mutual; keydata=
 xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2
 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04
 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX
 DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S
 P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU
 Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo
 UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC
 tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd
 wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0f
 UGFvbG8gQm9uemluaSA8Ym9uemluaUBnbnUub3JnPsLBTQQTAQIAIwUCVEJ7AwIbAwcLCQgH
 AwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEH4VEAzNNmmxNcwOniaZVLsuy1lW/ntYCA0Caz0i
 sHpmecK8aWlvL9wpQCk4GlOX9L1emyYXZPmzIYB0IRqmSzAlZxi+A2qm9XOxs5gJ2xqMEXX5
 FMtUH3kpkWWJeLqe7z0EoQdUI4EG988uv/tdZyqjUn2XJE+K01x7r3MkUSFz/HZKZiCvYuze
 VlS0NTYdUt5jBXualvAwNKfxEkrxeHjxgdFHjYWhjflahY7TNRmuqPM/Lx7wAuyoDjlYNE40
 Z+Kun4/KjMbjgpcF4Nf3PJQR8qXI6p3so2qsSn91tY7DFSJO6v2HwFJkC2jU95wxfNmTEUZc
 znXahYbVOwCDJRuPrE5GKFd/XJU9u5hNtr/uYipHij01WXal2cce1S5mn1/HuM1yo1u8xdHy
 IupCd57EWI948e8BlhpujUCU2tzOb2iYS0kpmJ9/oLVZrOcSZCcCl2P0AaCAsj59z2kwQS9D
 du0WxUs8waso0Qq6tDEHo8yLCOJDzSz4oojTtWe4zsulVnWV+wu70AioemAT8S6JOtlu60C5
 dHgQUD1Tp+ReXpDKXmjbASJx4otvW0qah3o6JaqO79tbDqIvncu3tewwp6c85uZd48JnIOh3
 utBAu684nJakbbvZUGikJfxd887ATQRUQnHuAQgAx4dxXO6/Zun0eVYOnr5GRl76+2UrAAem
 Vv9Yfn2PbDIbxXqLff7oyVJIkw4WdhQIIvvtu5zH24iYjmdfbg8iWpP7NqxUQRUZJEWbx2CR
 wkMHtOmzQiQ2tSLjKh/cHeyFH68xjeLcinR7jXMrHQK+UCEw6jqi1oeZzGvfmxarUmS0uRuf
 fAb589AJW50kkQK9VD/9QC2FJISSUDnRC0PawGSZDXhmvITJMdD4TjYrePYhSY4uuIV02v02
 8TVAaYbIhxvDY0hUQE4r8ZbGRLn52bEzaIPgl1p/adKfeOUeMReg/CkyzQpmyB1TSk8lDMxQ
 zCYHXAzwnGi8WU9iuE1P0wARAQABwsEzBBgBAgAJBQJUQnHuAhsMAAoJEH4VEAzNNmmxp1EO
 oJy0uZggJm7gZKeJ7iUpeX4eqUtqelUw6gU2daz2hE/jsxsTbC/w5piHmk1H1VWDKEM4bQBT
 uiJ0bfo55SWsUNN+c9hhIX+Y8LEe22izK3w7mRpvGcg+/ZRG4DEMHLP6JVsv5GMpoYwYOmHn
 plOzCXHvmdlW0i6SrMsBDl9rw4AtIa6bRwWLim1lQ6EM3PWifPrWSUPrPcw4OLSwFk0CPqC4
 HYv/7ZnASVkR5EERFF3+6iaaVi5OgBd81F1TCvCX2BEyIDRZLJNvX3TOd5FEN+lIrl26xecz
 876SvcOb5SL5SKg9/rCBufdPSjojkGFWGziHiFaYhbuI2E+NfWLJtd+ZvWAAV+O0d8vFFSvr
 iy9enJ8kxJwhC0ECbSKFY+W1eTIhMD3aeAKY90drozWEyHhENf4l/V+Ja5vOnW+gCDQkGt2Y
 1lJAPPSIqZKvHzGShdh8DduC0U3xYkfbGAUvbxeepjgzp0uEnBXfPTy09JGpgWbg0w91GyfT
 /ujKaGd4vxG2Ei+MMNDmS1SMx7wu0evvQ5kT9NPzyq8R2GIhVSiAd2jioGuTjX6AZCFv3ToO
 53DliFMkVTecLptsXaesuUHgL9dKIfvpm+rNXRn9wAwGjk0X/A==
Message-ID: <96bad133-077d-e27d-9f57-4df6399eb3b8@redhat.com>
Date:   Fri, 29 Jun 2018 12:45:20 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.8.0
MIME-Version: 1.0
In-Reply-To: <1530265876-18136-3-git-send-email-wanpengli@tencent.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 29/06/2018 11:51, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
> 
> Using hypercall to send IPIs by one vmexit instead of one by one for
> xAPIC/x2APIC physical mode and one vmexit per-cluster for x2APIC cluster 
> mode. 
> 
> Even if enable qemu interrupt remapping and PV TLB Shootdown, I can still 
> observe ~14% performance boost by ebizzy benchmark for 64 vCPUs VM, the 
> total msr-induced vmexits reduce ~70%.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
>  Documentation/virtual/kvm/cpuid.txt |  4 ++++
>  arch/x86/kvm/cpuid.c                |  3 ++-
>  arch/x86/kvm/x86.c                  | 25 +++++++++++++++++++++++++
>  include/uapi/linux/kvm_para.h       |  1 +
>  4 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
> index ab022dc..d72359f 100644
> --- a/Documentation/virtual/kvm/cpuid.txt
> +++ b/Documentation/virtual/kvm/cpuid.txt
> @@ -62,6 +62,10 @@ KVM_FEATURE_ASYNC_PF_VMEXIT        ||    10 || paravirtualized async PF VM exit
>                                     ||       || can be enabled by setting bit 2
>                                     ||       || when writing to msr 0x4b564d02
>  ------------------------------------------------------------------------------
> +KVM_FEATURE_PV_SEND_IPI            ||    11 || guest checks this feature bit
> +                                   ||       || before enabling paravirtualized
> +                                   ||       || send IPIs.

It's not "enabling" but "using".  You also need to document the
hypercall itself.

Paolo

> +------------------------------------------------------------------------------
>  KVM_FEATURE_CLOCKSOURCE_STABLE_BIT ||    24 || host will warn if no guest-side
>                                     ||       || per-cpu warps are expected in
>                                     ||       || kvmclock.
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 7e042e3..7bcfa61 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -621,7 +621,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
>  			     (1 << KVM_FEATURE_PV_UNHALT) |
>  			     (1 << KVM_FEATURE_PV_TLB_FLUSH) |
> -			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT);
> +			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT) |
> +			     (1 << KVM_FEATURE_PV_SEND_IPI);
>  
>  		if (sched_info_on())
>  			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0046aa7..c2e6cdb 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6689,6 +6689,27 @@ static void kvm_pv_kick_cpu_op(struct kvm *kvm, unsigned long flags, int apicid)
>  	kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL);
>  }
>  
> +static void kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap, u8 vector)
> +{
> +	struct kvm_apic_map *map;
> +	struct kvm_vcpu *vcpu;
> +	struct kvm_lapic_irq lapic_irq = {0};
> +	int i;
> +
> +	lapic_irq.delivery_mode = APIC_DM_FIXED;
> +	lapic_irq.vector = vector;
> +
> +	rcu_read_lock();
> +	map = rcu_dereference(kvm->arch.apic_map);
> +
> +	for_each_set_bit(i, &ipi_bitmap, sizeof(unsigned long)) {
> +		vcpu = map->phys_map[i]->vcpu;
> +		kvm_apic_set_irq(vcpu, &lapic_irq, NULL);
> +	}
> +
> +	rcu_read_unlock();
> +}
> +
>  void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
>  {
>  	vcpu->arch.apicv_active = false;
> @@ -6738,6 +6759,10 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>  		ret = kvm_pv_clock_pairing(vcpu, a0, a1);
>  		break;
>  #endif
> +	case KVM_HC_SEND_IPI:
> +		kvm_pv_send_ipi(vcpu->kvm, a0, a1);
> +		ret = 0;
> +		break;
>  	default:
>  		ret = -KVM_ENOSYS;
>  		break;
> diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
> index dcf629d..7395f38 100644
> --- a/include/uapi/linux/kvm_para.h
> +++ b/include/uapi/linux/kvm_para.h
> @@ -26,6 +26,7 @@
>  #define KVM_HC_MIPS_EXIT_VM		7
>  #define KVM_HC_MIPS_CONSOLE_OUTPUT	8
>  #define KVM_HC_CLOCK_PAIRING		9
> +#define KVM_HC_SEND_IPI         	10
>  
>  /*
>   * hypercalls use architecture specific
>