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

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Message-ID: <CABPqkBSmes+ee19iVh0EHvMQ=7TAzN3Fx1BKdOZ-2iuk5L0ugw@mail.gmail.com>
Date:	Sun, 16 Mar 2014 14:08:16 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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.

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?
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