Commit d12b524f authored Sep 20, 2011 by Thadeu Lima de Souza Cascardo Committed by Benjamin Herrenschmidt Sep 23, 2011

powerpc: Reserve iommu page 0

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>

parent 25c29f9e

arch/powerpc/kernel/iommu.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -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);