[PATCH AUTOSEL 5.2 01/76] powerpc: fix off by one in max_zone_pfn initialization for ZONE_DMA

[Sasha Levin]

From: Andrea Arcangeli <aarcange at redhat.com>

[ Upstream commit 03800e0526ee25ed7c843ca1e57b69ac2a5af642 ]

25078dc1f74be16b858e914f52cc8f4d03c2271a first introduced an off by
one error in the ZONE_DMA initialization of PPC_BOOK3E_64=y and since
9739ab7eda459f0669ec9807e0d9be5020bab88c the off by one applies to
PPC32=y too. This simply corrects the off by one and should resolve
crashes like below:

[   65.179101] page 0x7fff outside node 0 zone DMA [ 0x0 - 0x7fff ]

Unfortunately in various MM places "max" means a non inclusive end of
range. free_area_init_nodes max_zone_pfn parameter is one case and
MAX_ORDER is another one (unrelated) that comes by memory.

Reported-by: Zorro Lang <zlang at redhat.com>
Fixes: 25078dc1f74b ("powerpc: use mm zones more sensibly")
Fixes: 9739ab7eda45 ("powerpc: enable a 30-bit ZONE_DMA for 32-bit pmac")
Signed-off-by: Andrea Arcangeli <aarcange at redhat.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
Link: https://lore.kernel.org/r/20190625141727.2883-1-aarcange@redhat.com
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 arch/powerpc/mm/mem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 2540d3b2588c3..2eda1ec36f552 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -249,7 +249,7 @@ void __init paging_init(void)
 
 #ifdef CONFIG_ZONE_DMA
 	max_zone_pfns[ZONE_DMA]	= min(max_low_pfn,
-			((1UL << ARCH_ZONE_DMA_BITS) - 1) >> PAGE_SHIFT);
+				      1UL << (ARCH_ZONE_DMA_BITS - PAGE_SHIFT));
 #endif
 	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
 #ifdef CONFIG_HIGHMEM
-- 
2.20.1