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From:   "Wang, Wei W" <wei.w.wang@intel.com>
To:     "Christopherson,, Sean" <seanjc@google.com>
CC:     "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "dmatlack@google.com" <dmatlack@google.com>,
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        "eric.auger@redhat.com" <eric.auger@redhat.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "ikalvarado@google.com" <ikalvarado@google.com>
Subject: RE: [PATCH v1 05/18] KVM: selftests/hardware_disable_test: code
 consolidation and cleanup
Thread-Topic: [PATCH v1 05/18] KVM: selftests/hardware_disable_test: code
 consolidation and cleanup
Thread-Index: AQHY55yuIXKRns508k+BGhcyAkdsga4hY2oAgADNh4A=
Date:   Thu, 27 Oct 2022 14:14:00 +0000
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References: <20221024113445.1022147-1-wei.w.wang@intel.com>
 <20221024113445.1022147-6-wei.w.wang@intel.com> <Y1nNzO2tC+DCyKWI@google.com>
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On Thursday, October 27, 2022 8:16 AM, Sean Christopherson wrote:
> > diff --git a/tools/testing/selftests/kvm/hardware_disable_test.c
> >  static void run_test(uint32_t run)
> >  {
> >  	struct kvm_vcpu *vcpu;
> >  	struct kvm_vm *vm;
> >  	cpu_set_t cpu_set;
> > -	pthread_t threads[VCPU_NUM];
> >  	pthread_t throw_away;
> > -	void *b;
> > +	pthread_attr_t attr;
> >  	uint32_t i, j;
> > +	int r;
> >
> >  	CPU_ZERO(&cpu_set);
> >  	for (i =3D 0; i < VCPU_NUM; i++)
> >  		CPU_SET(i, &cpu_set);
>=20
> Uh, what is this test doing?  I assume the intent is to avoid spamming al=
l
> pCPUs in the system, but I don't get the benefit of doing so.

IIUIC, it is to test if the condition race between the 2 paths:
#1 kvm_arch_hardware_disable->drop_user_return_notifiers() and
#2 fire_user_return_notifiers->kvm_on_user_return
has been solved by disabling interrupts in kvm_on_user_return.

To stress the tests, it creates a bunch of threads (continuously making sys=
calls
to trigger #2 above) to be scheduled on the same pCPU that runs a vCPU, and
then VM is killed, which triggers #1 above.=20
They fork to test 512 times hoping there is chance #1 and #2 above can happ=
en
at the same time without an issue.

+ Ignacio to confirm if possible.