From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([140.186.70.92]:52320)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1R8Saf-0003jc-SL
	for qemu-devel@nongnu.org; Tue, 27 Sep 2011 04:00:37 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1R8Sae-0000aS-LM
	for qemu-devel@nongnu.org; Tue, 27 Sep 2011 04:00:33 -0400
Received: from mail-bw0-f45.google.com ([209.85.214.45]:59330)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@gmail.com>) id 1R8Sae-0000aH-99
	for qemu-devel@nongnu.org; Tue, 27 Sep 2011 04:00:32 -0400
Received: by bkbzv15 with SMTP id zv15so6822499bkb.4
	for <qemu-devel@nongnu.org>; Tue, 27 Sep 2011 01:00:31 -0700 (PDT)
Date: Tue, 27 Sep 2011 08:08:02 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20110927070802.GA8740@stefanha-thinkpad.localdomain>
References: <87litcs1ly.fsf@ginnungagap.bsc.es>
	<20110926075159.GA6455@stefanha-thinkpad.localdomain>
	<87r533piq5.fsf@ginnungagap.bsc.es>
	<87d3enp4f3.fsf@ginnungagap.bsc.es>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <87d3enp4f3.fsf@ginnungagap.bsc.es>
Subject: Re: [Qemu-devel] Help writing a trivial device
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: qemu-devel@nongnu.org
Cc: Avi Kivity <avi@redhat.com>

On Mon, Sep 26, 2011 at 08:03:12PM +0200, Lluís Vilanova wrote:
> #if 1                                   /* KVM doesn't like it */
>     s->data_ptr = g_malloc(s->size);
>     memory_region_init_ram_ptr(&s->data, &s->dev.qdev, "backdoor.data",
>                                s->size, s->data_ptr);
>     pci_register_bar(&s->dev, 1, PCI_BASE_ADDRESS_SPACE_MEMORY, &s->data);
> #endif

Have you tried page-aligning data_ptr with qemu_memalign() or doing an
anonymous mmap instead of g_malloc()?

>>From virt/kvm/kvm_main.c:__kvm_set_memory_region():

/* General sanity checks */
if (mem->memory_size & (PAGE_SIZE - 1))
	goto out;
if (mem->guest_phys_addr & (PAGE_SIZE - 1))
	goto out;
/* We can read the guest memory with __xxx_user() later on. */
if (user_alloc &&
    ((mem->userspace_addr & (PAGE_SIZE - 1)) ||
     !access_ok(VERIFY_WRITE,
		(void __user *)(unsigned long)mem->userspace_addr,
		mem->memory_size)))
	goto out;

Stefan