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Date: Mon, 11 May 2015 17:21:34 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 23/31] ich9: implement SMI_LOCK
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To: Laszlo Ersek <lersek@redhat.com>, kraxel@redhat.com
Cc: qemu-devel@nongnu.org, mst@redhat.com



On 11/05/2015 17:17, Laszlo Ersek wrote:
> If I understand correctly, this makes SMI_LOCK lock down the GBL_SMI_EN
> bit (and my OVMF patch that relies on that / tests it is satisfied too).
> 
> But, it doesn't seem to lock down APMC_EN. According to the ICH9 spec,
> it doesn't need to -- however when we discussed this earlier (see
> Message-Id: <553F4D23.3060305@redhat.com>), the idea was to lock down
> APMC_EN as well. (And I don't understand why the ICH9 spec / hw
> implementation doesn't lock APMC_EN; without that, APM_CNT won't
> necessarily trigger an SMI.)

I don't think it should.  See here
<https://lists.gnu.org/archive/html/qemu-devel/2015-04/msg02758.html>
where I wrote explicitly "Even if the OS tries to maliciously set
APMC_EN to 0 (SMI_LOCK doesn't lock APMC_EN)...".

Paolo