linux-kernel - Re: [PATCH 0/3] KVM: do not use kvm->online_vcpus to check "has one VCPU been created?"

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Message-Id: <575EB62F.4010107@de.ibm.com>
Date:	Mon, 13 Jun 2016 15:33:35 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc:	Cornelia Huck <cornelia.huck@...ibm.com>,
	Christian Borntraeger <christian.borntraeger@...ibm.com>
Subject: Re: [PATCH 0/3] KVM: do not use kvm->online_vcpus to check "has one
 VCPU been created?"

On 06/13/2016 03:25 PM, Paolo Bonzini wrote:
> kvm->online_vcpus is only updated at the very end of KVM_CREATE_VCPU.
> Thus, it can be racy to use it as a check for "has any VCPU been created
> already?".  While x86 detects the race through kvm_vcpu_compatible,
> it is kinda hackish and s390 does not do anything similar.  Provide a
> better fix for both.
> 
> Paolo Bonzini (3):
>   KVM: introduce created_vcpus
>   KVM: remove kvm_vcpu_compatible
>   KVM: s390: use created_vcpus
> 
>  arch/s390/kvm/kvm-s390.c | 10 +++++-----
>  arch/x86/kvm/Kconfig     |  1 -
>  arch/x86/kvm/x86.c       | 11 +++--------
>  include/linux/kvm_host.h | 14 ++++++++------
>  virt/kvm/Kconfig         |  3 ---
>  virt/kvm/kvm_main.c      | 27 +++++++++++++++++----------
>  6 files changed, 33 insertions(+), 33 deletions(-)
> 

>From a quick look this looks "the right thing". Will do a proper review
later this day or tomorrow.