Date:	Mon, 25 Aug 2008 09:17:09 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Yinghai Lu <yhlu.kernel@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Bernhard Walle <bwalle@...e.de>,
	Vivek Goyal <vgoyal@...hat.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: only put e820 ram entries in resource tree


* Eric W. Biederman <ebiederm@...ssion.com> wrote:

> Yinghai Lu <yhlu.kernel@...il.com> writes:
> 
> > may need user to have new kexec tools that could create e820 table
> > from /sys/firmware/memmap instead of /proc/iomem for second kernel
> 
> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> 
> /proc/iomem is mostly about io resources which you have just removed. 
> It is totally the wrong thing to only register RAM resource!

see the RFC commit below for more details - about the problem and 
various solutions we are thinking about. The core problem is that the 
problem was hard to find and hard to debug - it took the exception 
debugging effort of David Witbrodt to track it down.

So we are trying structural fixes to improve the situation. Just 
reverting the e820 changes breaks other things and is not the real fix 
anyway: the real fix is to increase communication between PC platform 
devices/drivers and the PCI code. DMI driven quirks are too limited as 
well - more such systems are suspected.
 
For now we've got the patch below from Yinghai - which hooks directly 
into the x86 PCI discovery and reallocation code. While that's already 
better than the initial DMI quirk, i think the real fix should go one 
level higher, to the resource manager.

i'd rather see the e820 reserved entries show up there (losing system 
setup information is almost always a bad idea - and the e820 map is 
central enough to be one of the more reliable BIOS-provided data 
structures), but with a different resource property: a 'sticky' resource 
bit which would cause overlapping PCI devices that already have their 
BAR programmed stay there. We already have a certain amount of support 
for 'container' resources (bridge resources for example).

That would automatically protect any hpet (or, in theory, ioapic) 
platform devices from the PCI code's currently blind resource 
reprogramming logic. These platform devices are not PCI enumerated so we 
cannot just make the platform drivers themselves be PCI drivers, and 
they are special in many regards. (often they are not PCI devices at 
all)

Note that this is only about the (BIOS provided) e820 map. The core 
problem is, inserting e820 map reserved entries as 'real' resources can 
break real devices.

	Ingo

---------------->
>From 1521c6b7a96e8d79c424216d9118859a017a4e9e Mon Sep 17 00:00:00 2001
From: Yinghai Lu <yhlu.kernel@...il.com>
Date: Sun, 24 Aug 2008 21:41:28 -0700
Subject: [PATCH] x86: fix HPET regression in 2.6.26 versus 2.6.25, check hpet against BAR v2

David Witbrodt tracked down (and bisected) a bootup hang on his system
to the following problem: a BIOS bug made the hpet device visible as a
generic PCI device. If e820 reserved entries happen to be registered
first in the resource tree [which v2.6.26 started doing - to fix other
bugs], then the PCI code will reallocate that device's BAR to some other
address - breaking timer IRQs and hanging the system.

( Normally hpet devices are hidden by the BIOS from the OS's PCI discovery
  via chipset magic. Sometimes the hpet is not a PCI device at all. )

Solve this fundamental fragility by making the non-PCI platform driver
insert resources into the resource tree even if it overlaps the e820
reserved entry, to keep the resource manager from updating the BAR.

NOTE: this is an RFC for now, there might be other, better approaches
      as well:

 - introduce a new resource type that is 'sticky': it would keep BARs
   that are embedded in it from being reallocated.

or

 - update the hpet_address from the PCI code. This is risky though: these
   PCI devices are often non-generic and might break if we change their
   BAR.

or

 - do not insert e820 reserved entries at all. This would have
   disadvantages as well: if there's some special non-RAM ACPI or SMM
   area known to the system and enumerated in the e820 map, we must not
   allow the PCI code from possibly allocating a resource into that
   region.

[ mingo@...e.hu: cleanups ]

Bisected-by: David Witbrodt <dawitbro@...global.net>
Signed-off-by: Yinghai Lu <yhlu.kernel@...il.com>
Tested-by: David Witbrodt <dawitbro@...global.net>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/pci/i386.c |   44 ++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 44 insertions(+), 0 deletions(-)

diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index 5807d1b..57be547 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -28,6 +28,7 @@
 #include <linux/kernel.h>
 #include <linux/pci.h>
 #include <linux/init.h>
+#include <linux/hpet.h>
 #include <linux/ioport.h>
 #include <linux/errno.h>
 #include <linux/bootmem.h>
@@ -78,6 +79,47 @@ pcibios_align_resource(void *data, struct resource *res,
 EXPORT_SYMBOL(pcibios_align_resource);
 
 /*
+ * Make sure we protect magic platform devices such as hpet,
+ * even if they show up in PCI discovery. (which should really
+ * not happen, but it does on some broken BIOSen)
+ */
+static int check_platform(struct pci_dev *dev, struct resource *res)
+{
+	unsigned long base;
+	unsigned long size;
+
+	base = res->start;
+	size = (res->start == 0 && res->end == res->start) ? 0 :
+		 (res->end - res->start + 1);
+
+	if (!base || !size)
+		return 0;
+
+#ifdef CONFIG_HPET_TIMER
+	/* for hpet */
+	if (base == hpet_address && (res->flags & IORESOURCE_MEM)) {
+		struct resource *root = NULL;
+
+		WARN("BAR has HPET at %08lx-%08lx\n", base, base + size - 1);
+		/*
+		 * forcibly insert it into the
+		 * resource tree
+		 */
+		if (res->flags & IORESOURCE_MEM)
+			root = &iomem_resource;
+		else if (res->flags & IORESOURCE_IO)
+			root = &ioport_resource;
+
+		if (root)
+			insert_resource(root, res);
+		return 1;
+	}
+#endif
+
+	return 0;
+}
+
+/*
  *  Handle resources of PCI devices.  If the world were perfect, we could
  *  just allocate all the resource regions and do nothing more.  It isn't.
  *  On the other hand, we cannot just re-allocate all devices, as it would
@@ -171,6 +213,8 @@ static void __init pcibios_allocate_resources(int pass)
 					r->flags, disabled, pass);
 				pr = pci_find_parent_resource(dev, r);
 				if (!pr || request_resource(pr, r) < 0) {
+					if (check_platform(dev, r))
+						continue;
 					dev_err(&dev->dev, "BAR %d: can't "
 						"allocate resource\n", idx);
 					/* We'll assign a new address later */
--
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