linux-kernel - RE: [PATCH v2 1/1] drivers:hv:vmbus drivers:hv:vmbus Allow for more than one MMIO range for children

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Date:	Sat, 7 Feb 2015 04:57:48 +0000
From:	Jake Oshins <jakeo@...rosoft.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	KY Srinivasan <kys@...rosoft.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>
Subject: RE: [PATCH v2 1/1] drivers:hv:vmbus drivers:hv:vmbus Allow for more
 than one MMIO range for children

> > -----Original Message-----
> > From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> > Sent: Friday, February 6, 2015 7:04 AM
> > To: Jake Oshins
> > Cc: gregkh@...uxfoundation.org; KY Srinivasan; linux-kernel@...r.kernel.org;
> > devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com
> > Subject: Re: [PATCH v2 1/1] drivers:hv:vmbus drivers:hv:vmbus Allow for more
> > than one MMIO range for children
<snip>
> >
> > Sorry for beeing late with this message but I'm seeing issues with this
> > commit. I added some debug to figure out what's going on and here is
> > what I see:
> >
> > With Gen1 VM we end up doing request_resource for two ranges:
> > f8000000 - fffbffff
> > fe0000000 - fffefffff
> >
> > request_resource() fails (as we already have PCI device at f8000000 I
> > suppose?) but we don't check the return value. release_resource on
> > module unload crashes the kernel:
> > [   78.314344] BUG: unable to handle kernel NULL pointer dereference at
> > 0000000000000030
> > [   78.315021] IP: [<ffffffff8107fac5>] release_resource+0x25/0x90
> > [   78.315021] PGD 78c67067 PUD 78c5a067 PMD 0
> > [   78.315021] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
> > [   78.315021] Modules linked in: hv_vmbus(-)
> > ...
> > If I'm not mistaken, before the change we didn't do any
> > request_resource() for Gen1 VMs at all.
> >
> > With Gen2 VM we do request_resource for fe0000000 - fffffffff range
> > only, that means this commit doesn't change anything.
> >
> > Can you please take a look? I'd like to help but I don't completely
> > understand the essense of the change wrt Gen1 VMs with PCI devices.
> >
> 
> I'll take a look immediately.
> 
> Thanks,
> Jake

I looked at this and I realize that I need to fix this problem structurally.  The intent is that VMBus-enumerated paravirtual "devices" suballocate from everything granted to the ACPI node above VMBus, in its _CRS object.  But since PCI devices also have to suballocate from those ranges, I need a different approach.  I'll work up a fix for this and send it around for review.

-- Jake Oshins

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