linux-kernel - Re: [PATCH] x86: kvm: reset the bootstrap processor when it gets an INIT

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Message-ID: <513DAE8F.3050102@redhat.com>
Date:	Mon, 11 Mar 2013 11:14:39 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	mtosatti@...hat.com, jan.kiszka@...mens.com
Subject: Re: [PATCH] x86: kvm: reset the bootstrap processor when it gets
 an INIT

Il 10/03/2013 19:10, Gleb Natapov ha scritto:
> On Sun, Mar 10, 2013 at 06:19:07PM +0100, Paolo Bonzini wrote:
>> Il 10/03/2013 16:35, Gleb Natapov ha scritto:
>>>>> However, it would effectively redefine the meaning of
>>>>> KVM_MP_STATE_INIT_RECEIVED and KVM_MP_STATE_SIPI_RECEIVED, respectively
>>>>> to KVM_MP_STATE_WAIT_FOR_SIPI and KVM_MP_STATE_RESETTING.  I wasn't sure
>>>>> if this is considered an API change (personally, I would treat it as one).
>>>>>
>>> If it is kernel module internal it definitely is not API change.
>>> INIT/SIPI handling is a bit ad-hoc right now anyway as Jan noticed. For
>>> instance INIT does not really resets VCPU. Only after SIPI it is really
>>> reset, so KVM_MP_STATE_SIPI_RECEIVED is really KVM_MP_STATE_RESET_ME_RIGHT_NOW
>>> state.
>>
>> Yeah, and the current definition is ambiguous (without hypervisor
>> patches, there's no way to use it as the names would suggest), so
>> perhaps the right thing to do is to rename the states (old names kept
>> for backwards compatibility only) and work from there.
>>
> I do not see how renaming clarify things. From userspace point of view
> KVM_MP_STATE_SIPI_RECEIVED does not exists.

Not really true---we do exit with that state and EINTR when we get a
SIPI.  Perhaps that can be changed.

> If AP is hard reset
> userspase makes it UNINIT, if soft reset it makes it INIT_RECEIVED, if
> BSP it makes it running no matter what type of reset.

The current name just suggests . 
And when getting an INIT in the in-kernel LAPIC, this:

-			vcpu->arch.mp_state = KVM_MP_STATE_INIT_RECEIVED;
+			vcpu->arch.mp_state = kvm_vcpu_is_bsp(vcpu) ?
+				KVM_MP_STATE_SIPI_RECEIVED :
+				KVM_MP_STATE_INIT_RECEIVED;

makes much less sense than this:

-			vcpu->arch.mp_state = KVM_MP_STATE_WAIT_FOR_SIPI;
+			vcpu->arch.mp_state = kvm_vcpu_is_bsp(vcpu) ?
+				KVM_MP_STATE_RESET_NOW :
+				KVM_MP_STATE_WAIT_FOR_SIPI;

However, there's also Jan's plans for nVMX.  Peeking at his queue (see
http://git.kiszka.org/?p=linux-kvm.git;a=commitdiff;h=037fb24ec) I think
it's better to always reflect INITs to the hypervisor like I did in these
patches.

Paolo
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