wrong usage of MAX_DMA_ADDRESS in bootmem.h
- From: Nicolas Pitre <nico@xxxxxxx>
- Date: Tue, 30 Sep 2008 15:35:01 -0400 (EDT)
I have implemented highmem for ARM. To catch wrong usage of __pa() and
__va() with out of range values, I added a range check when
CONFIG_DEBUG_HIGHMEM is set.
One issue is that bootmem.h uses __pa(MAX_DMA_ADDRESS). However
MAX_DMA_ADDRESS on ARM is defined as 0xffffffff because there is usually
no restriction on the maximum DMA-able address.
RMK suggested that those places should be using ISA_DMA_THRESHOLD
instead -- here's an excert of our conversation on this topic:
I suspect all those places which are doing __pa(MAX_DMA_ADDRESS) really
want to be using ISA_DMA_THRESHOLD - that's something to raise on LKML
if it's causing problems.
Given the definition I've just given, if there's no restrictions on
what can be DMA'd from, defining 'MAX_DMA_ADDRESS' to a constant well
in excess of the maximum amount of RAM is quite reasonable. Since most
ARM platforms don't have any restrictions on memory that can be DMA'd,
the existing code is perfectly reasonable and correct.
It falls apart when the range check on values passed to __pa() is
enabled in a highmem context.
As I say, having it in excess of the real amount of RAM fitted is not a
problem. Unfortunately, it makes the range check fall apart but I suspect
that's because of inappropriate use.
So what about this patch?
diff --git a/include/linux/bootmem.h b/include/linux/bootmem.h
index 95837bf..7a97ffe 100644
--- a/include/linux/bootmem.h
+++ b/include/linux/bootmem.h
@@ -96,21 +96,21 @@ extern void *__alloc_bootmem_low_node(pg_data_t *pgdat,
unsigned long goal);
#ifndef CONFIG_HAVE_ARCH_BOOTMEM_NODE
#define alloc_bootmem(x) \
- __alloc_bootmem(x, SMP_CACHE_BYTES, __pa(MAX_DMA_ADDRESS))
+ __alloc_bootmem(x, SMP_CACHE_BYTES, ISA_DMA_THRESHOLD)
#define alloc_bootmem_nopanic(x) \
- __alloc_bootmem_nopanic(x, SMP_CACHE_BYTES, __pa(MAX_DMA_ADDRESS))
+ __alloc_bootmem_nopanic(x, SMP_CACHE_BYTES, ISA_DMA_THRESHOLD)
#define alloc_bootmem_low(x) \
__alloc_bootmem_low(x, SMP_CACHE_BYTES, 0)
#define alloc_bootmem_pages(x) \
- __alloc_bootmem(x, PAGE_SIZE, __pa(MAX_DMA_ADDRESS))
+ __alloc_bootmem(x, PAGE_SIZE, ISA_DMA_THRESHOLD)
#define alloc_bootmem_pages_nopanic(x) \
- __alloc_bootmem_nopanic(x, PAGE_SIZE, __pa(MAX_DMA_ADDRESS))
+ __alloc_bootmem_nopanic(x, PAGE_SIZE, ISA_DMA_THRESHOLD)
#define alloc_bootmem_low_pages(x) \
__alloc_bootmem_low(x, PAGE_SIZE, 0)
#define alloc_bootmem_node(pgdat, x) \
- __alloc_bootmem_node(pgdat, x, SMP_CACHE_BYTES, __pa(MAX_DMA_ADDRESS))
+ __alloc_bootmem_node(pgdat, x, SMP_CACHE_BYTES, ISA_DMA_THRESHOLD)
#define alloc_bootmem_pages_node(pgdat, x) \
- __alloc_bootmem_node(pgdat, x, PAGE_SIZE, __pa(MAX_DMA_ADDRESS))
+ __alloc_bootmem_node(pgdat, x, PAGE_SIZE, ISA_DMA_THRESHOLD)
#define alloc_bootmem_low_pages_node(pgdat, x) \
__alloc_bootmem_low_node(pgdat, x, PAGE_SIZE, 0)
#endif /* !CONFIG_HAVE_ARCH_BOOTMEM_NODE */
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