Re: [PATCH v2] KVM: x86: Convert INIT and SIPI signals into synchronously handled requests

[Jan Kiszka <jan.kiszka@web.de>]

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On 2013-03-06 07:12, Paolo Bonzini wrote:
> 
>> On Tue, Mar 05, 2013 at 08:16:41PM -0300, Marcelo Tosatti wrote:
>>> On Mon, Mar 04, 2013 at 10:41:43PM +0100, Jan Kiszka wrote:
>>>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>>>
>>>> A VCPU sending INIT or SIPI to some other VCPU races for setting
>>>> the
>>>> remote VCPU's mp_state. When we were unlucky,
>>>> KVM_MP_STATE_INIT_RECEIVED
>>>> was overwritten by kvm_emulate_halt and, thus, got lost.
>>>>
>>>> Fix this by raising requests on the sender side that will then be
>>>> handled synchronously over the target VCPU context.
>>>>
>>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>>>
>>> Why is kvm_emulate_halt being executed from
>>> KVM_MP_STATE_INIT_RECEIVED/KVM_MP_STATE_SIPI_RECEIVED again?
>>>
>>> Why is it not true that the only valid transition from
>>> KVM_MP_STATE_HALTED is from KVM_MP_STATE_RUNNABLE?
>>
>> See Paolo's table, it is. So why fix a race which should not be
>> happening in the first place.
> 
> The bad transition happens exactly because of the race.
> Are you saying you prefer the solution with cmpxchg?

I think we are past that point in our discussion and should really
separate signal (INIT/SIPI) from state (INIT/SIPI_RECEIVED etc.).

Jan



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