From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752152AbbKJXog (ORCPT <rfc822;w@1wt.eu>);
	Tue, 10 Nov 2015 18:44:36 -0500
Received: from mail-ob0-f181.google.com ([209.85.214.181]:35749 "EHLO
	mail-ob0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751123AbbKJXob (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 10 Nov 2015 18:44:31 -0500
MIME-Version: 1.0
In-Reply-To: <1447194427.31884.100.camel@kernel.crashing.org>
References: <cover.1446162273.git.luto@kernel.org> <20151109133624-mutt-send-email-mst@redhat.com>
 <1447109937.31884.42.camel@kernel.crashing.org> <CALCETrX7Gkw3WrBHff=TpCFHj444E8hHcR6sAqOghQFBo5wp_A@mail.gmail.com>
 <1447121076.31884.61.camel@kernel.crashing.org> <CALCETrW5_bKCX5gKYaH5y4rvD9jrjY5O5d=oX8hHtAM9EE2Bew@mail.gmail.com>
 <1447133316.31884.67.camel@kernel.crashing.org> <CALCETrVPQc04Ah7FXcRMb4RhpUJ1WPCoC_4dbacB8a+u5XpmwA@mail.gmail.com>
 <1447151874.31884.82.camel@kernel.crashing.org> <CALCETrVkE3=KCxK-_bf-P8UfTS96Vck+QPE8EsLvP7THxpLe1A@mail.gmail.com>
 <1447194427.31884.100.camel@kernel.crashing.org>
From: Andy Lutomirski <luto@amacapital.net>
Date: Tue, 10 Nov 2015 15:44:10 -0800
Message-ID: <CALCETrWb9poeyxXhcbAbQkpcP-XYjWtz2w9iSPkKJH8rdzAj-A@mail.gmail.com>
Subject: Re: [PATCH v4 0/6] virtio core DMA API conversion
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Sebastian Ott <sebott@linux.vnet.ibm.com>,
        "David S. Miller" <davem@davemloft.net>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Cornelia Huck <cornelia.huck@de.ibm.com>,
        Joerg Roedel <jroedel@suse.de>, KVM <kvm@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        sparclinux@vger.kernel.org
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Nov 10, 2015 at 2:27 PM, Benjamin Herrenschmidt
<benh@kernel.crashing.org> wrote:
> On Tue, 2015-11-10 at 10:54 -0800, Andy Lutomirski wrote:
>>
>> Does that work on powerpc on existing kernels?
>>
>> Anyway, here's another crazy idea: make the quirk assume that the
>> IOMMU is bypasses if and only if the weak barriers bit is set on
>> systems that are missing the new DT binding.
>
> "New DT bindings" doesn't mean much ... how do we change DT bindings on
> existing machines with a FW in flash ?
>
> What about partition <-> partition virtio such as what we could do on
> PAPR systems. That would have the weak barrier bit.
>

Is it partition <-> partition, bypassing IOMMU?

I think I'd settle for just something that doesn't regress
non-experimental setups that actually work today and that allow new
setups (x86 with fixed QEMU and maybe something more complicated on
powerpc and/or sparc) to work in all cases.

We could certainly just make powerpc and sparc continue bypassing the
IOMMU until someone comes up with a way to fix it.  I'll send out some
patches that do that, and maybe that'll help this make progress.

--Andy