Message-ID: <20080825073125.GA27950@elte.hu>
Date:	Mon, 25 Aug 2008 09:31:25 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	David Witbrodt <dawitbro@...global.net>,
	Linux-kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: HPET regression in 2.6.26 versus 2.6.25 -- found another user
	with the same regression


* Yinghai Lu <yhlu.kernel@...il.com> wrote:

> this one should work. please apply this one only.
> 
> YH
>
> [PATCH] x86: check hpet with BAR v2

great. I've cleaned it up a bit (see the final commit below) and queued 
it up in tip/x86/urgent for some testing. But there are a few open 
questions, and an Ack/feedback from Jesse/Linus would be nice as well:

- the forced insertion and the embedded knowledge about iomem_resource
  and ioport_resource looks ugly to me.

- we should also extend this to other platform resource types that we 
  know about: ioapic address(es) might be a prime candidate. (local 
  APICs are CPU entities and should never show up as PCI devices) The 
  mmconfig range is already properly accounted for by the PCI code 
  itself, right?

- plus a more highlevel approach would be nice as well i think - making 
  sure that the hpet driver runs before any of the PCI code, and 
  inserting a special "sticky" resource there which would keep any 
  potential followup generic PCI resource that overlaps this resource 
  untouched. (with a proper kernel warning emitted as well - such 
  situations are likely BIOS bugs.)

Possibly not for v2.6.27 though.

	Ingo

----------->
>From f3865e9710bd4ac5750feae628469f998e49d0b4 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..562ec4d 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -33,6 +33,7 @@
 #include <linux/bootmem.h>
 
 #include <asm/pat.h>
+#include <asm/hpet.h>
 
 #include "pci.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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