From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:59342)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1YIgA7-0006fB-Rq
	for qemu-devel@nongnu.org; Tue, 03 Feb 2015 11:17:20 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1YIgA4-0005zq-IO
	for qemu-devel@nongnu.org; Tue, 03 Feb 2015 11:17:15 -0500
Received: from mail-qa0-x235.google.com ([2607:f8b0:400d:c00::235]:37067)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <rth7680@gmail.com>) id 1YIgA4-0005zm-D2
	for qemu-devel@nongnu.org; Tue, 03 Feb 2015 11:17:12 -0500
Received: by mail-qa0-f53.google.com with SMTP id n4so34527880qaq.12
	for <qemu-devel@nongnu.org>; Tue, 03 Feb 2015 08:17:12 -0800 (PST)
Sender: Richard Henderson <rth7680@gmail.com>
Message-ID: <54D0F482.9020709@twiddle.net>
Date: Tue, 03 Feb 2015 08:17:06 -0800
From: Richard Henderson <rth@twiddle.net>
MIME-Version: 1.0
References: <1421428797-23697-1-git-send-email-fred.konrad@greensocs.com>
	<1421428797-23697-3-git-send-email-fred.konrad@greensocs.com>
In-Reply-To: <1421428797-23697-3-git-send-email-fred.konrad@greensocs.com>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [RFC 02/10] use a different translation block list
 for each cpu.
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: fred.konrad@greensocs.com, qemu-devel@nongnu.org, mttcg@greensocs.com
Cc: peter.maydell@linaro.org, pbonzini@redhat.com, mark.burton@greensocs.com, agraf@suse.de, jan.kiszka@siemens.com

On 01/16/2015 09:19 AM, fred.konrad@greensocs.com wrote:
> @@ -759,7 +760,9 @@ static void page_flush_tb_1(int level, void **lp)
>          PageDesc *pd = *lp;
>  
>          for (i = 0; i < V_L2_SIZE; ++i) {
> -            pd[i].first_tb = NULL;
> +            for (j = 0; j < MAX_CPUS; j++) {
> +                pd[i].first_tb[j] = NULL;
> +            }
>              invalidate_page_bitmap(pd + i);
>          }
>      } else {

Surely you've got to do some locking somewhere in order to be able to modify
another thread's cpu tb list.

I realize that we do have to solve this problem for x86, but for most other
targets we ought, in principal, be able to avoid it.  Which simply requires
that we not treat icache flushes as nops.

When the kernel has modified a page, like so, it will also have notified the
other cpus that like so,

        if (smp_call_function(ipi_flush_icache_page, mm, 1)) {

We ought to be able to leverage this to avoid some locking at the qemu level.


r~