From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@novell.com>
Subject: RE: iommu=0 leading to panic when system defaults
	to using x2apic
Date: Tue, 14 Dec 2010 08:21:51 +0000
Message-ID: <4D07372F0200007800027BBF@vpn.id2.novell.com>
References: <4D0215E0020000780002734A@vpn.id2.novell.com>
	<C927C3C4.C5DD%keir@xen.org>
	<4D0224E602000078000273AD@vpn.id2.novell.com>
	<749B9D3DBF0F054390025D9EAFF47F22317AA2F4@shsmsx501.ccr.corp.intel.com>
	<4D0257D7020000780002747B@vpn.id2.novell.com>
	<987664A83D2D224EAE907B061CE93D530193BB9EB8@orsmsx505.amr.corp.intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: quoted-printable
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <987664A83D2D224EAE907B061CE93D530193BB9EB8@orsmsx505.amr.corp.intel.com>
Content-Disposition: inline
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Allen M Kay <allen.m.kay@intel.com>, Yang Z Zhang <yang.z.zhang@intel.com>
Cc: Keir Fraser <keir@xen.org>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Weidong Han <weidong.han@intel.com>
List-Id: xen-devel@lists.xenproject.org

>>> On 10.12.10 at 19:26, "Kay, Allen M" <allen.m.kay@intel.com> wrote:
> The architectural requirement is actually between interrupt remapping =
and=20
> x2apic.  Since interrupt remapping is part of the VT-d feature so =
current=20
> software requires all VT-d features enabled in order for x2apic to be =
enabled.
>=20
> Strictly speaking DMA remapping is not required for x2apic.  However, =
queued=20
> invalidation is required since interrupt remapping requires queued=20
> invalidation.  So x2apic dependency is as follows:
>=20
>     x2apic->interrupt remapping->queued invalidation
>=20
> Due to historical reasons, the new VT-d features were built on top of =
the old=20
> ones as they become available.  Is there a requirement to separate this =
out? =20
> If so, we will need to re-design iommu boot parameter which took a while =
to=20
> get it right so most systems can now boot successfully.

And why is it that Xen panics when the BIOS pre-enabled x2apic
mode without also enabling interrupt re-mapping, while Linux
(afaict from looking at 2.6.32 code and output from an affected
machine) simply enables interrupt re-mapping in this case?

Thanks, Jan