Re: [patch] Ignore MCFG if the mmconfig area isn't reserved in thee820 table

[Arjan van de Ven]

On Thu, 2006-03-23 at 20:02 +0100, Arjan van de Ven wrote:
> > That is e820_mapped(address, address+size, E820_RESERVED)
> > 
> > And not having a size is definitely wrong on i386 too.
> 
> s/wrong/not selective enough/
> 
> and e820_mapped doesn't check this either anyway, at least not the way
> you imply it does.
> 
> I'll do a new patch using this for x86_64 though, no need to make a
> second function like this.


There have been several machines that don't have a working MMCONFIG,
often because of a buggy MCFG table in the ACPI bios. This patch adds a
simple sanity check that detects a whole bunch of these cases, and when
it detects it, linux now boots rather than crash-and-burns. The accuracy
of this detection can in principle be improved if there was a "is this
entire range in e820 with THIS attribute", but no such function exist
and the complexity needed for this is not really worth it; this simple
check already catches most cases anyway.

Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>

diff -purN linux-2.6.16/arch/i386/kernel/setup.c linux-2.6.16-mmconfig/arch/i386/kernel/setup.c
--- linux-2.6.16/arch/i386/kernel/setup.c	2006-03-20 06:53:29.000000000 +0100
+++ linux-2.6.16-mmconfig/arch/i386/kernel/setup.c	2006-03-23 20:06:22.000000000 +0100
@@ -1377,6 +1377,27 @@ static void __init register_memory(void)
 		pci_mem_start, gapstart, gapsize);
 }
 
+/*
+ * Check if an address is reserved in the e820 map
+ */
+int is_e820_reserved(u64 address)
+{
+	int	      i;
+	i = e820.nr_map;
+	while (--i >= 0) {
+		unsigned long long start = e820.map[i].addr;
+		unsigned long long end = start + e820.map[i].size;
+
+		if (address <=end && address >= start) {
+			if (e820.map[i].type == E820_RESERVED)
+				return 1;
+			else
+				return 0;
+		}
+	}
+	return 0;
+}
+
 /* Use inline assembly to define this because the nops are defined 
    as inline assembly strings in the include files and we cannot 
    get them easily into strings. */
diff -purN linux-2.6.16/arch/i386/pci/mmconfig.c linux-2.6.16-mmconfig/arch/i386/pci/mmconfig.c
--- linux-2.6.16/arch/i386/pci/mmconfig.c	2006-03-20 06:53:29.000000000 +0100
+++ linux-2.6.16-mmconfig/arch/i386/pci/mmconfig.c	2006-03-23 20:06:22.000000000 +0100
@@ -12,6 +12,7 @@
 #include <linux/pci.h>
 #include <linux/init.h>
 #include <linux/acpi.h>
+#include <asm/e820.h>
 #include "pci.h"
 
 #define mmcfg_virt_addr ((void __iomem *) fix_to_virt(FIX_PCIE_MCFG))
@@ -183,6 +184,17 @@ static int __init pci_mmcfg_init(void)
 	    (pci_mmcfg_config[0].base_address == 0))
 		goto out;
 
+	/*
+	 * several bioses have a buggy MCFG table. While this is hard
+	 * to test for conclusively, we know the value is defective
+	 * if the memory isn't marked reserved in the e820 table
+	 */
+	if (!is_e820_reserved(pci_mmcfg_config[0].base_address)) {
+		printk(KERN_INFO "PCI: BIOS Bug: MCFG area is not reserved\n");
+		printk(KERN_INFO "PCI: Not using MMCONFIG.\n");
+		goto out;
+	}
+
 	printk(KERN_INFO "PCI: Using MMCONFIG\n");
 	raw_pci_ops = &pci_mmcfg;
 	pci_probe = (pci_probe & ~PCI_PROBE_MASK) | PCI_PROBE_MMCONF;
diff -purN linux-2.6.16/arch/x86_64/kernel/e820.c linux-2.6.16-mmconfig/arch/x86_64/kernel/e820.c
--- linux-2.6.16/arch/x86_64/kernel/e820.c	2006-03-20 06:53:29.000000000 +0100
+++ linux-2.6.16-mmconfig/arch/x86_64/kernel/e820.c	2006-03-23 20:05:33.000000000 +0100
@@ -80,6 +80,11 @@ static inline int bad_addr(unsigned long
 	return 0;
 } 
 
+/* 
+ * This function returns 1 if any part of the <start, end> range is in the
+ * E820 map having "type". There may be parts in this range that are not in 
+ * E820 at all and/or parts with different types in addition.
+ */
 int __init e820_mapped(unsigned long start, unsigned long end, unsigned type) 
 { 
 	int i;
diff -purN linux-2.6.16/arch/x86_64/pci/mmconfig.c linux-2.6.16-mmconfig/arch/x86_64/pci/mmconfig.c
--- linux-2.6.16/arch/x86_64/pci/mmconfig.c	2006-03-20 06:53:29.000000000 +0100
+++ linux-2.6.16-mmconfig/arch/x86_64/pci/mmconfig.c	2006-03-23 20:08:21.000000000 +0100
@@ -9,6 +9,7 @@
 #include <linux/init.h>
 #include <linux/acpi.h>
 #include <linux/bitmap.h>
+#include <asm/e820.h>
 #include "pci.h"
 
 #define MMCONFIG_APER_SIZE (256*1024*1024)
@@ -161,6 +162,19 @@ static int __init pci_mmcfg_init(void)
 	    (pci_mmcfg_config[0].base_address == 0))
 		return 0;
 
+	/*
+	 * several bioses have a buggy MCFG table. While this is hard
+	 * to test for conclusively, we know the value is defective
+	 * if the memory isn't marked reserved in the e820 table
+	 */
+	if (!e820_mapped(pci_mmcfg_config[0].base_address,
+			pci_mmcfg_config[0].base_address + MMCONFIG_APER_SIZE, 
+			E820_RESERVED)) {
+		printk(KERN_INFO "PCI: BIOS Bug: MCFG area is not reserved\n");
+		printk(KERN_INFO "PCI: Not using MMCONFIG.\n");
+		return 0;
+	}
+
 	/* RED-PEN i386 doesn't do _nocache right now */
 	pci_mmcfg_virt = kmalloc(sizeof(*pci_mmcfg_virt) * pci_mmcfg_config_num, GFP_KERNEL);
 	if (pci_mmcfg_virt == NULL) {
diff -purN linux-2.6.16/include/asm-i386/e820.h linux-2.6.16-mmconfig/include/asm-i386/e820.h
--- linux-2.6.16/include/asm-i386/e820.h	2006-03-20 06:53:29.000000000 +0100
+++ linux-2.6.16-mmconfig/include/asm-i386/e820.h	2006-03-23 20:06:22.000000000 +0100
@@ -35,6 +35,9 @@ struct e820map {
 };
 
 extern struct e820map e820;
+
+extern int is_e820_reserved(u64 address);
+
 #endif/*!__ASSEMBLY__*/
 
 #endif/*__E820_HEADER*/

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