Commit 850fc430 authored by Danesh Petigara's avatar Danesh Petigara Committed by Linus Torvalds

mm: cma: fix CMA aligned offset calculation

The CMA aligned offset calculation is incorrect for non-zero order_per_bit

For example, if cma->order_per_bit=1, cma->base_pfn= 0x2f800000 and
align_order=12, the function returns a value of 0x17c00 instead of 0x400.

This patch fixes the CMA aligned offset calculation.

The previous calculation was wrong and would return too-large values for
the offset, so that when cma_alloc looks for free pages in the bitmap with
the requested alignment > order_per_bit, it starts too far into the bitmap
and so CMA allocations will fail despite there actually being plenty of
free pages remaining.  It will also probably have the wrong alignment.
With this change, we will get the correct offset into the bitmap.

One affected user is powerpc KVM, which has kvm_cma->order_per_bit set to

[ changelog additions]
Signed-off-by: default avatarDanesh Petigara <>
Reviewed-by: default avatarGregory Fong <>
Acked-by: default avatarMichal Nazarewicz <>
Cc: <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 44fc8057
......@@ -64,15 +64,17 @@ static unsigned long cma_bitmap_aligned_mask(struct cma *cma, int align_order)
return (1UL << (align_order - cma->order_per_bit)) - 1;
* Find a PFN aligned to the specified order and return an offset represented in
* order_per_bits.
static unsigned long cma_bitmap_aligned_offset(struct cma *cma, int align_order)
unsigned int alignment;
if (align_order <= cma->order_per_bit)
return 0;
alignment = 1UL << (align_order - cma->order_per_bit);
return ALIGN(cma->base_pfn, alignment) -
(cma->base_pfn >> cma->order_per_bit);
return (ALIGN(cma->base_pfn, (1UL << align_order))
- cma->base_pfn) >> cma->order_per_bit;
static unsigned long cma_bitmap_maxno(struct cma *cma)
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