Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932098Ab1EYXiE (ORCPT ); Wed, 25 May 2011 19:38:04 -0400 Received: from mga09.intel.com ([134.134.136.24]:6530 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754351Ab1EYXh6 (ORCPT ); Wed, 25 May 2011 19:37:58 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.65,270,1304319600"; d="p7s'?scan'208";a="4937934" From: "Woodhouse, David" To: Thomas Gleixner CC: Ingo Molnar , "Song, Youquan" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "hpa@zytor.com" , "hpa@linux.intel.com" , "Kay, Allen M" , "Siddha, Suresh B" , "Sankaran, Rajesh" , "Mallick, Asit K" , "Liu, Kent" , Youquan Song Date: Thu, 26 May 2011 00:37:50 +0100 Subject: Re: [PATCH v4] x86, vt-d: enable x2apic opt out Thread-Topic: [PATCH v4] x86, vt-d: enable x2apic opt out Thread-Index: AcwbNMOay65JVompRrC18IUJrua3rA== Message-ID: <1306366670.2029.46.camel@i7.infradead.org> References: <1306341418-10645-1-git-send-email-youquan.song@intel.com> <20110525205843.GC28397@elte.hu> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: yes X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: multipart/signed; micalg=sha1; protocol="application/x-pkcs7-signature"; boundary="=-tJBxkfpXP31SWzSLlUDW" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10469 Lines: 164 --=-tJBxkfpXP31SWzSLlUDW Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2011-05-25 at 23:01 +0100, Thomas Gleixner wrote: > On Wed, 25 May 2011, Ingo Molnar wrote: > > So why isnt the x2apic disabled in the CPUID? That's the canonical=20 > > way to unsupport a particular non-working CPU hw feature. A valid question. Rajesh? > Because some committee decided to make it an ACPI feature. > That's broken by design, but you can't change the stupid spec retroactive= ly. You can ask for clarification of the stupid spec though. :) Is it *really* tied to interrupt-remapping, as the wording in the spec implies? In particular, what about the case where VT-d has been disabled in the BIOS so there is *no* DMAR table at all, and hence nowhere for this 'opt out' bit to be set? Currently, it looks like we still enable x2apic in that case. We have a *build* time dependency which means you can't build x2apic support unless you also build interrupt-remapping support. But unless there's a lot of dead code in our x2apic support, it looks like we still enable x2apic at run time if we didn't enable IR for various reasons. Is that going to make these broken BIOSes fall over too? If so, it really does look like the placement of this bit in the DMAR table is entirely wrong. Rajesh, can you tell use *exactly* what is the BIOS brokenness that this hack was invented to work around? --=20 David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation --=-tJBxkfpXP31SWzSLlUDW Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIVTDCCAz0w ggKmoAMCAQICAwWw/zANBgkqhkiG9w0BAQUFADBOMQswCQYDVQQGEwJVUzEQMA4GA1UEChMHRXF1 aWZheDEtMCsGA1UECxMkRXF1aWZheCBTZWN1cmUgQ2VydGlmaWNhdGUgQXV0aG9yaXR5MB4XDTA2 MDIxNjE4MDEzMFoXDTE2MDIxOTE4MDEzMFowUjELMAkGA1UEBhMCVVMxGjAYBgNVBAoTEUludGVs IENvcnBvcmF0aW9uMScwJQYDVQQDEx5JbnRlbCBFeHRlcm5hbCBCYXNpYyBQb2xpY3kgQ0EwggEi MA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQDBpd/XOb9QVqEZ8mQ1042TdOIq3ATDIsV2xDyt 30yLyMR5Wjtus0bn3B+he89BiNO/LP6+rFzEwlD55PlX+HLGIKeNNG97dqyc30FElEUjZzTZFq2N 4e3kVJ/XAEEgANzV8v9qp7qWwxugPgfc3z9BkYot+CifozexHLb/hEZj+yISCU61kRZvuSQ0E11y 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