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powerpc: Reserve iommu page 0

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Some devices have a dma-window that starts at the address 0. This allows
DMA addresses to be mapped to this address and returned to drivers as a
valid DMA address. Some drivers may not behave well in this case, since
the address 0 is considered an error or not allocated.

The solution to avoid this kind of error from happening is reserve the
page addressed as 0 so it cannot be allocated for a DMA mapping.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Thadeu Lima de Souza Cascardo 2011-09-20 03:07:24 +00:00 committed by Benjamin Herrenschmidt
parent 25c29f9e32
commit d12b524f8b
1 changed files with 8 additions and 0 deletions
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8
arch/powerpc/kernel/iommu.c
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@ -501,6 +501,14 @@ struct iommu_table *iommu_init_table(struct iommu_table *tbl, int nid)
tbl->it_map = page_address(page);
memset(tbl->it_map, 0, sz);
/*
* Reserve page 0 so it will not be used for any mappings.
* This avoids buggy drivers that consider page 0 to be invalid
* to crash the machine or even lose data.
*/
if (tbl->it_offset == 0)
set_bit(0, tbl->it_map);
tbl->it_hint = 0;
tbl->it_largehint = tbl->it_halfpoint;
spin_lock_init(&tbl->it_lock);