Messages in this thread Patch in this message | | | Date | Tue, 30 Sep 2008 15:35:01 -0400 (EDT) | From | Nicolas Pitre <> | Subject | wrong usage of MAX_DMA_ADDRESS in bootmem.h |
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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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