From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:37304)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kraxel@redhat.com>) id 1Ykpip-0006DH-72
	for qemu-devel@nongnu.org; Wed, 22 Apr 2015 04:09:28 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <kraxel@redhat.com>) id 1Ykpil-0000Z2-7c
	for qemu-devel@nongnu.org; Wed, 22 Apr 2015 04:09:27 -0400
Received: from mx1.redhat.com ([209.132.183.28]:40849)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <kraxel@redhat.com>) id 1Ykpil-0000Yu-06
	for qemu-devel@nongnu.org; Wed, 22 Apr 2015 04:09:23 -0400
Received: from int-mx13.intmail.prod.int.phx2.redhat.com
	(int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26])
	by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id t3M89Lqu011522
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256
	verify=FAIL)
	for <qemu-devel@nongnu.org>; Wed, 22 Apr 2015 04:09:21 -0400
Message-ID: <1429690157.14806.43.camel@nilsson.home.kraxel.org>
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Wed, 22 Apr 2015 10:09:17 +0200
In-Reply-To: <1429628650.21164.24.camel@nilsson.home.kraxel.org>
References: <1429521560-2743-1-git-send-email-kraxel@redhat.com>
	<1429521560-2743-5-git-send-email-kraxel@redhat.com>
	<55365C33.2090101@redhat.com>
	<1429628650.21164.24.camel@nilsson.home.kraxel.org>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH 5/6] [wip] tseg, part1, not (yet) tested
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Laszlo Ersek <lersek@redhat.com>
Cc: pbonzini@redhat.com, qemu-devel@nongnu.org, mst@redhat.com

  Hi,

> tseg is just normal ram (yes, located at the end of memory), but (once
> tseg is enabled) only cpus in smm mode are allowed to access it.
> Likewise busmaster dma access is rejected, so non-smm code can't use the
> sata controller to access this indirectly.

Update:  Seems tseg can be anywhere, there is a "tseg memory base"
register @ 0xac in pci config space.

Placing it at the end of memory is just what the bios is supposed to do
by default.  And it makes sense to place it there.

<quote>
This register contains the base address of TSEG DRAM memory. BIOS
determines the base of TSEG memory by subtracting the TSEG size (PCI
Device 0, offset 9Eh, bits 2:1) from graphics GTT stolen base (PCI
Device 0, offset A8h, bits 31:20).

Once D_LCK has been set, these bits becomes read only.
</quote>

"GTT stolen base" equals "top of below-4g memory" for us because we
emulate the chipset variant without graphics in qemu.

cheers,
  Gerd