linux-kernel - RE: [PATCH v1 05/18] KVM: selftests/hardware_disable

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Message-ID: <DS0PR11MB63739599621057805F4AB391DC329@DS0PR11MB6373.namprd11.prod.outlook.com>
Date:   Fri, 28 Oct 2022 02:16:55 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "vipinsh@...gle.com" <vipinsh@...gle.com>,
        "ajones@...tanamicro.com" <ajones@...tanamicro.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ikalvarado@...gle.com" <ikalvarado@...gle.com>
Subject: RE: [PATCH v1 05/18] KVM: selftests/hardware_disable_test: code
 consolidation and cleanup

On Friday, October 28, 2022 2:03 AM, Sean Christopherson wrote:
> But why does it matter what pCPU a vCPU is running on?  Wouldn't the
> probability of triggering a race between kvm_on_user_return() and
> hardware_disable() be _higher_ if there are more pCPUs returning to userspace?

I think the point there is that the vcpus and those syscall threads need to be on the
same pCPUs. Linux by default has its own load balancing for threads to run on. If the
vcpus and syscall threads are scattered on different pCPUs, kvm_on_user_return
would less likely to be triggered when the syscall threads return to userspace.