[PATCH] [1/8] GBPAGES: Handle kernel near memory hole in clear_kernel_mapping

[Andi Kleen]

This was a long standing obscure problem in the relocatable kernel. The
AMD GART driver needs to unmap part of the GART in the kernel direct mapping to 
prevent cache corruption. With the relocatable kernel it is in theory possible 
that the separate kernel text mapping straddles that area too. 

Normally it should not happen because GART tends to be >= 2GB, and the kernel 
is normally not loaded that high, but it is possible in theory. 

Teach clear_kernel_mapping() about this case.

This will become more important once the kernel mapping uses 1GB pages.

Cc: ebiederm@xxxxxxxxxxxx
Cc: vgoyal@xxxxxxxxxx

Signed-off-by: Andi Kleen <ak@xxxxxxx>

---
 arch/x86/mm/init_64.c |   20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

Index: linux/arch/x86/mm/init_64.c
===================================================================
--- linux.orig/arch/x86/mm/init_64.c
+++ linux/arch/x86/mm/init_64.c
@@ -411,7 +411,8 @@ void __init paging_init(void)
    from the CPU leading to inconsistent cache lines. address and size
    must be aligned to 2MB boundaries. 
    Does nothing when the mapping doesn't exist. */
-void __init clear_kernel_mapping(unsigned long address, unsigned long size) 
+static void __init
+__clear_kernel_mapping(unsigned long address, unsigned long size)
 {
 	unsigned long end = address + size;
 
@@ -441,6 +442,23 @@ void __init clear_kernel_mapping(unsigne
 	__flush_tlb_all();
 } 
 
+#define overlaps(as,ae,bs,be) ((ae) >= (bs) && (as) <= (be))
+
+void __init clear_kernel_mapping(unsigned long address, unsigned long size)
+{
+	int sh = PMD_SHIFT;
+	unsigned long kernel = __pa(__START_KERNEL_map);
+
+	if (overlaps(kernel>>sh, (kernel + KERNEL_TEXT_SIZE)>>sh,
+			__pa(address)>>sh, __pa(address + size)>>sh)) {
+		printk(KERN_INFO
+			"Kernel at %lx overlaps memory hole at %lx-%lx\n",
+				kernel, __pa(address), __pa(address+size));
+		__clear_kernel_mapping(__START_KERNEL_map+__pa(address), size);
+	}
+	__clear_kernel_mapping(address, size);
+}
+
 /*
  * Memory hotplug specific functions
  */
--
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