linux-kernel - Re: Info: mapping multiple BARs. Your kernel is fine.

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Message-ID: <1425376.F2qgSAxAbW@vostro.rjw.lan>
Date:	Mon, 17 Mar 2014 01:09:39 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	lkml <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Linux PCI <linux-pci@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: Info: mapping multiple BARs. Your kernel is fine.

On Sunday, March 16, 2014 02:08:16 PM Stephane Eranian wrote:
> Rafael,
> 
> Thanks for the analysis.
> 
> On Sun, Mar 16, 2014 at 12:55 PM, Borislav Petkov <bp@...en8.de> wrote:
> > On Sat, Mar 15, 2014 at 03:15:04PM +0100, Rafael J. Wysocki wrote:
> >> I've just gone throught this.
> >
> > Thanks.
> >
> >> So the problem is that we have the PNP "system" driver whose only purpose seems
> >> to be to reserve system resources so that the PCI layer doesn't assign them to
> >> new devices on hotplug (disclaimer: I didn't invent it, I only read the code and
> >> comments in there).
> >>
> >> It does that for ACPI device objects having the "PNP0C02" and "PNP0C01" IDs.
> >
> > Right, pnp 00:01 is PNP0C02.
> >
> >> Apparently, snb_uncore_imc_init_box() steps on a range already reserved by that
> >> driver on your box.  And this doesn't seem to be a coincidence, because the ACPI
> >> device object in question probably *does* correspond to the memory controller
> >> that the uncore driver attempts to use.
> >>
> >> I'm not sure how to address that right now to be honest.  Arguably, the PNP
> >> "system" driver should be replaced with something saner, but still the
> >> resources it claims need to be kept out of reach of the PCI's resource
> >> allocation code.
> >
> > Well, I'm only conjecturing here but there should be a way for the
> > uncore code to tell the PNP "system" driver to free this resource
> > because uncore is going to use it now. Or something to that effect.
> >
> I agree. The snb_uncore_imc() is making real (good) use of the device.
> It needs to own it. So we need a way to free the resource from the PNP
> system or  a way to tell PNP need to grab it on systems with the
> snb_uncore_imc() support. Does that kind of API exist?
> 
> Where do I look to prevent PNP from grabbing the IMC?

drivers/pnp/system.c is the driver in question and system_pnp_probe() makes
the reservations via reserve_resources_of_dev(), so you'd need to modify that.

I'm not sure what's the right way to go here, though.

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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