From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:51223)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <aarcange@redhat.com>) id 1Uz9df-0004T0-4w
	for qemu-devel@nongnu.org; Tue, 16 Jul 2013 14:06:19 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <aarcange@redhat.com>) id 1Uz9dW-0008W0-Jh
	for qemu-devel@nongnu.org; Tue, 16 Jul 2013 14:06:15 -0400
Date: Tue, 16 Jul 2013 20:06:03 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
Message-ID: <20130716180603.GD23279@redhat.com>
References: <1373995321-2470-1-git-send-email-aarcange@redhat.com>
	<20130716173844.GC19826@otherpad.lan.raisama.net>
	<51E586E6.1060001@redhat.com> <51E5876B.2040500@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <51E5876B.2040500@redhat.com>
Subject: Re: [Qemu-devel] [PATCH] fix guest physical bits to match host,
 to go beyond 1TB guests
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: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-stable@nongnu.org, Eduardo Habkost <ehabkost@redhat.com>, Gleb Natapov <gleb@redhat.com>, qemu-devel@nongnu.org

-On Tue, Jul 16, 2013 at 07:48:27PM +0200, Paolo Bonzini wrote:
> Il 16/07/2013 19:46, Paolo Bonzini ha scritto:
> >>> >> (see PUD with bit >=40 set)
> >> > 
> >> > I am not sure I understand what caused this: if we are advertising 40
> >> > physical bits to the guest, why are we ending up with a PUD with
> >> > bit >= 40 set?
> > Because we create a guest that has bigger memory than what we advertise
> > in CPUID.
> > 
> 
> Also, note that the guest does not really care about this CPUID.  It is
> only used by KVM itself to decide which bits in the page tables are
> reserved.

Yes, I suppose guests thinks if there's >1TB of RAM there are enough
bits in the pagetables to map whatever RAM "range" was found.

About migrating >1TB guests it will be possible as soon as qemu starts
to use the remap_anon_pages+MADV_USERFAULT two features I posted on
linux-kernel recently. With those two features, qemu should start to
provide postcopy live migration by default and after pre-copy is
complete, it will never need to freeze a guest in the source node
anymore.