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

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Date:	Mon, 11 Mar 2013 15:23:01 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Jan Kiszka <jan.kiszka@...mens.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

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.

Paolo
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