Message-ID: <513DBF45.9030803@redhat.com>
Date: Mon, 11 Mar 2013 12:25:57 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130219 Thunderbird/17.0.3
MIME-Version: 1.0
To: Gleb Natapov <gleb@redhat.com>
CC: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, mtosatti@redhat.com,
        jan.kiszka@siemens.com
Subject: Re: [PATCH] x86: kvm: reset the bootstrap processor when it gets
 an INIT
References: <1362811713-25830-1-git-send-email-pbonzini@redhat.com> <20130310114646.GM11223@redhat.com> <513C9E82.1020304@redhat.com> <20130310153540.GL24444@redhat.com> <513CC08B.2040800@redhat.com> <20130310181035.GM24444@redhat.com> <513DAE8F.3050102@redhat.com> <20130311102852.GE31619@redhat.com>
In-Reply-To: <20130311102852.GE31619@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2150
Lines: 54

Il 11/03/2013 11:28, Gleb Natapov ha scritto:
>> Not really true---we do exit with that state and EINTR when we get a
>> SIPI.  Perhaps that can be changed.
>
> That's implementation detail. We can jump to the beginning of the
> function instead. Nowhere we document that entering
> KVM_MP_STATE_SIPI_RECEIVED state cause KVM_RUN return with EINTR.

Yes, that would be nice.

>>> 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;
>>
> Both of them are equally incorrect. INIT should cause reset, and only if
> vmx is off. An userspace reset is also completely broken in that regard.
> Renaming things gives us nothing, only bring unneeded churn. If the
> names were internal I wouldn't mind, but they are APIs.
> 
>> 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.
>>
> The commit was before we decided that we should not abuse mp_state for
> signaling.

Agreed, but we still have the problem of how to signal from userspace.
For that do you have any other suggestion than mp_state?  And if we keep
mp_state to signal from userspace, giving INIT_RECEIVED the
"wait-for-SIPI" semantics would be wrong.

Paolo

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/