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 S1755684Ab3LDLIS (ORCPT <rfc822;w@1wt.eu>);
	Wed, 4 Dec 2013 06:08:18 -0500
Received: from smtp.citrix.com ([66.165.176.89]:52677 "EHLO SMTP.CITRIX.COM"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1755485Ab3LDLIQ (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 4 Dec 2013 06:08:16 -0500
X-IronPort-AV: E=Sophos;i="4.93,824,1378857600"; 
   d="scan'208";a="80446932"
Message-ID: <1386155291.17466.19.camel@kazak.uk.xensource.com>
Subject: Re: [PATCH] xen/pvhvm: If xen_platform_pci=0 is set don't blow up.
From: Ian Campbell <Ian.Campbell@citrix.com>
To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        <xen-devel@lists.xenproject.org>, <linux-kernel@vger.kernel.org>,
        <boris.ostrovsky@oracle.com>, <david.vrabel@citrix.com>,
        <leosilva@linux.vnet.ibm.com>, <ashley@ashleylai.com>,
        <peterhuewe@gmx.de>, <mail@srajiv.net>, <tpmdd@selhorst.net>,
        <tpmdd@sirrix.com>, <dmitry.torokhov@gmail.com>, <bhelgaas@google.com>,
        <plagnioj@jcrosoft.com>, <tomi.valkeinen@ti.com>,
        <tpmdd-devel@lists.sourceforge.net>, <linux-input@vger.kernel.org>,
        <netdev@vger.kernel.org>, <linux-pci@vger.kernel.org>,
        <linux-fbdev@vger.kernel.org>
Date: Wed, 4 Dec 2013 11:08:11 +0000
In-Reply-To: <alpine.DEB.2.02.1312041104110.7093@kaball.uk.xensource.com>
References: <1386105246-14337-1-git-send-email-konrad.wilk@oracle.com>
	  <1386149848.13256.86.camel@kazak.uk.xensource.com>
	  <alpine.DEB.2.02.1312041049310.7093@kaball.uk.xensource.com>
	 <1386154783.17466.14.camel@kazak.uk.xensource.com>
	 <alpine.DEB.2.02.1312041104110.7093@kaball.uk.xensource.com>
Organization: Citrix Systems, Inc.
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.4.4-3 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
X-Originating-IP: [10.80.2.80]
X-DLP: MIA2
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 2013-12-04 at 11:05 +0000, Stefano Stabellini wrote:
> On Wed, 4 Dec 2013, Ian Campbell wrote:
> > On Wed, 2013-12-04 at 10:51 +0000, Stefano Stabellini wrote:
> > > On Wed, 4 Dec 2013, Ian Campbell wrote:
> > > > > +bool xen_has_pv_devices(void)
> > > > > +{
> > > > > +	if (!xen_domain())
> > > > > +		return false;
> > > > > +
> > > > > +	if (xen_hvm_domain()) {
> > > > > +		/* User requested no unplug, so no PV drivers. */
> > > > > +		if (xen_emul_unplug & XEN_UNPLUG_NEVER)
> > > > > +			return false;
> > > > 
> > > > I think you need
> > > > 		if (xen_emul_unpug & XEN_UNPLUG_UNNECESSARY)
> > > > 			return true;
> > > > don't you?
> > > 
> > > XEN_UNPLUG_UNNECESSARY was introduced to enable the platform PCI device
> > > even if it didn't respond properly to the unplug protocol.
> > > The corresponding parameter is called "unnecessary" because if you pass
> > > it to the kernel you mean that it is unnecessary to unplug the emulated
> > > devices but you can use the pv devices anyway.
> > > 
> > > So no, we shouldn't check for XEN_UNPLUG_UNNECESSARY here.
> > 
> > Oh, we will eventually fall through to the return true, so it does
> > actually work out OK.
> > 
> > I'd still be in favour of handling each option explicitly, for clarity.
> > Which means checking for XEN_UNPLUG_UNNECESSARY.
> 
> I think is wrong to check for any xen_emul_unpug options in this function.
> The xen_emul_unpug options should be used to set the right value of
> xen_platform_pci_unplug. (See my other reply.)

Whichever one we check we should still be checking explicitly for the
"unnecessary" case, for clarity if nothing else.

TBH I think the split between xen_emul_unplug and
xen_platform_pci_unplug is a bit artificial. There should be one value
which is static to platform-pci-unplug.c and accessor functions should
be provided for other code to use. Open coding all those accesses to
xen_platform_pci_unplug in every driver is just too error prone.

Ian.