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From: Paolo Bonzini <pbonzini@redhat.com>
To: Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc: "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
	<linux-kernel@vger.kernel.org>, Jim Mattson <jmattson@google.com>,
	Joerg Roedel <joro@8bytes.org>, Borislav Petkov <bp@alien8.de>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH v2 5/8] KVM: x86: APICv: fix race in kvm_request_apicv_update on SVM
Date: Tue, 27 Jul 2021 00:34:54 +0200	[thread overview]
Message-ID: <e8acf99c-0e3b-f0cc-c8ad-53074420d734@redhat.com> (raw)
In-Reply-To: <20210713142023.106183-6-mlevitsk@redhat.com>

On 13/07/21 16:20, Maxim Levitsky wrote:
> +	mutex_lock(&vcpu->kvm->apicv_update_lock);
> +
>  	vcpu->arch.apicv_active = kvm_apicv_activated(vcpu->kvm);
>  	kvm_apic_update_apicv(vcpu);
>  	static_call(kvm_x86_refresh_apicv_exec_ctrl)(vcpu);
> @@ -9246,6 +9248,8 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu)
>  	 */
>  	if (!vcpu->arch.apicv_active)
>  		kvm_make_request(KVM_REQ_EVENT, vcpu);
> +
> +	mutex_unlock(&vcpu->kvm->apicv_update_lock);

Does this whole piece of code need the lock/unlock?  Does it work and/or 
make sense to do the unlock immediately after mutex_lock()?  This makes 
it clearer that the mutex is being to synchronize against the requestor.

> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index ed4d1581d502..ba5d5d9ebc64 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -943,6 +943,7 @@ static struct kvm *kvm_create_vm(unsigned long type)
>   	mutex_init(&kvm->irq_lock);
>   	mutex_init(&kvm->slots_lock);
>   	mutex_init(&kvm->slots_arch_lock);
> +	mutex_init(&kvm->apicv_update_lock);
>   	INIT_LIST_HEAD(&kvm->devices);
>   
>   	BUILD_BUG_ON(KVM_MEM_SLOTS_NUM > SHRT_MAX);
> 

Please add comments above fields that are protected by this lock 
(anything but apicv_inhibit_reasons?), and especially move it to kvm->arch.

Paolo


  reply	other threads:[~2021-07-26 22:35 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-13 14:20 [PATCH v2 0/8] My AVIC patch queue Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 1/8] KVM: SVM: svm_set_vintr don't warn if AVIC is active but is about to be deactivated Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 2/8] KVM: SVM: tweak warning about enabled AVIC on nested entry Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 3/8] KVM: SVM: use vmcb01 in svm_refresh_apicv_exec_ctrl Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 4/8] KVM: x86: APICv: drop immediate APICv disablement on current vCPU Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 5/8] KVM: x86: APICv: fix race in kvm_request_apicv_update on SVM Maxim Levitsky
2021-07-26 22:34   ` Paolo Bonzini [this message]
2021-07-27 13:22     ` Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 6/8] KVM: SVM: add warning for mistmatch between AVIC state and AVIC access page state Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 7/8] KVM: SVM: call avic_vcpu_load/avic_vcpu_put when enabling/disabling AVIC Maxim Levitsky
2021-07-13 14:20 ` [PATCH v2 8/8] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use Maxim Levitsky
2021-07-18 12:13   ` Maxim Levitsky
2021-07-19  7:47     ` Vitaly Kuznetsov
2021-07-19  9:00       ` Maxim Levitsky
2021-07-19  9:23         ` Vitaly Kuznetsov
2021-07-19  9:58           ` Maxim Levitsky
2021-07-19 18:49     ` Sean Christopherson
2021-07-20  9:40       ` Maxim Levitsky
2021-07-22  9:12       ` KVM's support for non default APIC base Maxim Levitsky
2021-08-02  9:20         ` Maxim Levitsky
2021-08-06 21:55         ` Sean Christopherson
2021-08-09  9:40           ` Maxim Levitsky
2021-08-09 15:57             ` Sean Christopherson
2021-08-09 16:47             ` Jim Mattson
2021-08-10 20:42               ` Maxim Levitsky
2021-07-22 17:35       ` [PATCH v2 8/8] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use Maxim Levitsky
2021-07-22 19:06         ` Sean Christopherson
2021-07-27 13:05           ` Maxim Levitsky
2021-07-27 17:48             ` Ben Gardon
2021-07-27 18:17               ` Sean Christopherson
2021-07-29 14:10                 ` Maxim Levitsky
2021-07-26 17:24 ` [PATCH v2 0/8] My AVIC patch queue Paolo Bonzini

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