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

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Date:	Mon, 11 Mar 2013 16:36:33 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
CC:	Gleb Natapov <gleb@...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 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.

Jan

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