[PATCH] x86_64: make GART PTEs uncacheable

["Joachim Deguara" <joachim.deguara@amd.com>]

This patches fixes the silent data corruption problems being seen using the 
GART iommu where 4kB of data where incorrect (seen mostly on Nvidia CK804 
systems).  This fix, to mark the memory regin the GART PTEs reside on as 
uncacheable, also brings the code in line with the AGP specification.

Signed-off-by: Joachim Deguara <joachim.deguara@amd.com>

---
diff --git a/arch/x86_64/kernel/pci-gart.c b/arch/x86_64/kernel/pci-gart.c
index 2bac8c6..0bae862 100644
--- a/arch/x86_64/kernel/pci-gart.c
+++ b/arch/x86_64/kernel/pci-gart.c
@@ -519,7 +519,11 @@ static __init int init_k8_gatt(struct ag
 	gatt_size = (aper_size >> PAGE_SHIFT) * sizeof(u32); 
 	gatt = (void *)__get_free_pages(GFP_KERNEL, get_order(gatt_size)); 
 	if (!gatt) 
-		panic("Cannot allocate GATT table"); 
+		panic("Cannot allocate GATT table");
+	if (change_page_attr_addr((unsigned long)gatt, gatt_size >> PAGE_SHIFT, 
PAGE_KERNEL_NOCACHE))
+		panic("Could not set GART PTEs to uncacheable pages");
+	global_flush_tlb();
+
 	memset(gatt, 0, gatt_size); 
 	agp_gatt_table = gatt;