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

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Message-ID: <513E158B.80506@siemens.com>
Date:	Mon, 11 Mar 2013 18:34:03 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Paolo Bonzini <pbonzini@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mtosatti@...hat.com" <mtosatti@...hat.com>
Subject: Re: [PATCH] x86: kvm: reset the bootstrap processor when it gets
 an INIT

On 2013-03-11 18:23, Gleb Natapov wrote:
> On Mon, Mar 11, 2013 at 04:36:33PM +0100, Jan Kiszka wrote:
>> On 2013-03-11 15:23, Paolo Bonzini wrote:
>>> Il 11/03/2013 15:05, Gleb Natapov ha scritto:
>>>> On Mon, Mar 11, 2013 at 03:01:40PM +0100, Jan Kiszka wrote:
>>>>>> We are not moving away from mp_state, we are moving away from using
>>>>>> mp_state for signaling because with nested virt INIT does not always
>>>>>> change mp_state, not only that it can change mp_state long after signal
>>>>>> is received after vmx off is done.
>>>>>
>>>>> Right.
>>>>>
>>>>> BTW, for that to happen, we will also need to influence the INIT level.
>>>>> Unless I misread the spec, INIT is blocked while in root mode, and if
>>>>> you deassert INIT before leaving root (vmxoff, vmenter), nothing
>>>>> actually happens. So what matters is the INIT signal level at the exit
>>>>> of root mode.
>>>>>
>>>> You are talking about INIT# signal received via CPU pin, right? I think
>>>> INIT send by IPI cannot go away.
>>>
>>> Neither can go away.  For INIT sent by IPI, 10.4.7 says:
>>>
>>> Only the Pentium and P6 family processors support the INIT-deassert IPI.
>>> An INIT-disassert IPI has no affect on the state of the APIC, other than
>>> to reload the arbitration ID register with the value in the APIC ID
>>> register.
>>>
>>> 18.27.1 also says that "In the local APIC, NMI and INIT (except for INIT
>>> deassert) are always treated as edge triggered interrupts".
>>>
>>>
>>> For INIT#, the ICH9 chipset says that "INIT# is driven low for 16 PCI
>>> clocks" when a soft reset is requested.  So we can guess that INIT# is
>>> also edge-triggered.
>>
>> Ah, ok. So, virtually, INIT stays asserted until it can be delivered in
>> form of a reset or a vmexit.
>>
> vmexit clears it?

It has to. Otherwise, it would hit the host on vmxoff.

The spec says: "The INIT signal is blocked whenever a logical processor
is in VMX root operation. It is not blocked in VMX non-root operation.
Instead, INITs cause VM exits [...]."

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux
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