x86: max_low_pfn_mapped fix, #1

fix crash on Ingo's big box:

calling  pci_iommu_init+0x0/0x17
PCI-DMA: Disabling AGP.
PCI-DMA: aperture base @ d0000000 size 65536 KB
PCI-DMA: using GART IOMMU.
PCI-DMA: Reserving 64MB of IOMMU area in the AGP aperture
BUG: unable to handle kernel paging request at ffff88000003be88
IP: [<ffffffff8026d377>] __alloc_pages_internal+0xc3/0x3f2
PGD 202063 PUD 206063 PMD 22fc00163 PTE 3b162
Oops: 0000 [1] SMP

and e820 is:

 BIOS-e820: 0000000000000000 - 000000000009ac00 (usable)
 BIOS-e820: 000000000009ac00 - 00000000000a0000 (reserved)
 BIOS-e820: 00000000000ca000 - 0000000000100000 (reserved)
 BIOS-e820: 0000000000100000 - 000000007ff70000 (usable)
 BIOS-e820: 000000007ff70000 - 000000007ff86000 (ACPI data)
 BIOS-e820: 000000007ff86000 - 0000000080000000 (ACPI NVS)
 BIOS-e820: 0000000080000000 - 00000000cfe00000 (usable)
 BIOS-e820: 00000000cfe00000 - 00000000d0000000 (reserved)
 BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)
 BIOS-e820: 00000000fec00000 - 00000000fec10000 (reserved)
 BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
 BIOS-e820: 00000000fff80000 - 0000000100000000 (reserved)
 BIOS-e820: 0000000100000000 - 0000000830000000 (usable)

system has 32 GB RAM installed.

max_low_pfn_mapped is 0xcfe00, and GART aperture is not mapped.

So try to use init_memory_mapping to map that area, because the iommu
thinks that area is ram ...

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/pci-gart_64.c

@@ -630,6 +630,7 @@ static __init int init_k8_gatt(struct agp_kern_info *info)
 	struct pci_dev *dev;
 	void *gatt;
 	int i, error;
+	unsigned long start_pfn, end_pfn;
 
 	printk(KERN_INFO "PCI-DMA: Disabling AGP.\n");
 	aper_size = aper_base = info->aper_size = 0;
@@ -674,6 +675,16 @@ static __init int init_k8_gatt(struct agp_kern_info *info)
 
 	printk(KERN_INFO "PCI-DMA: aperture base @ %x size %u KB\n",
 	       aper_base, aper_size>>10);
+
+	/* need to map that range */
+	end_pfn = (aper_base>>PAGE_SHIFT) + (aper_size>>PAGE_SHIFT);
+	if (end_pfn > max_low_pfn_mapped) {
+		start_pfn = max_low_pfn_mapped;
+		max_low_pfn_mapped = init_memory_mapping(start_pfn<<PAGE_SHIFT,
+							 end_pfn<<PAGE_SHIFT);
+		if (max_pfn_mapped < max_low_pfn_mapped)
+			max_pfn_mapped = max_low_pfn_mapped;
+	}
 	return 0;
 
  nommu: