On Thu, Oct 23, 2014 at 05:33:47PM +0300, Laurent Pinchart wrote:
> Commit 95b0e655f914 ("ARM: mm: don't limit default CMA region only to
> low memory") extended CMA memory reservation to allow usage of high
> memory. It relied on commit f7426b983a6a ("mm: cma: adjust address limit
> to avoid hitting low/high memory boundary") to ensure that the reserved
> block never crossed the low/high memory boundary. While the
> implementation correctly lowered the limit, it failed to consider the
> case where the base..limit range crossed the low/high memory boundary
> with enough space on each side to reserve the requested size on either
> low or high memory.
>
> Rework the base and limit adjustment to fix the problem. The function
> now starts by rejecting the reservation altogether for fixed
> reservations that cross the boundary, then adjust the limit if
> reservation from high memory is impossible, and finally first try to
> reserve from high memory first and then falls back to low memory.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx>
> ---
> mm/cma.c | 58 ++++++++++++++++++++++++++++++++++++++++++++--------------
> 1 file changed, 44 insertions(+), 14 deletions(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index 6b14346..b83597b 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -247,23 +247,38 @@ int __init cma_declare_contiguous(phys_addr_t base,
> return -EINVAL;
>
> /*
> - * adjust limit to avoid crossing low/high memory boundary for
> + * Adjust limit and base to avoid crossing low/high memory boundary for
> * automatically allocated regions
> */
> - if (((limit == 0 || limit > memblock_end) &&
> - (memblock_end - size < highmem_start &&
> - memblock_end > highmem_start)) ||
> - (!fixed && limit > highmem_start && limit - size < highmem_start)) {
> - limit = highmem_start;
> - }
>
> - if (fixed && base < highmem_start && base+size > highmem_start) {
> + /*
> + * If allocating at a fixed base the request region must not cross the
> + * low/high memory boundary.
> + */
> + if (fixed && base < highmem_start && base + size > highmem_start) {
> ret = -EINVAL;
> pr_err("Region at %08lx defined on low/high memory boundary (%08lx)\n",
> (unsigned long)base, (unsigned long)highmem_start);
> goto err;
> }
>
> + /*
> + * If the limit is unspecified or above the memblock end, its effective
> + * value will be the memblock end. Set it explicitly to simplify further
> + * checks.
> + */
> + if (limit == 0 || limit > memblock_end)
> + limit = memblock_end;
> +
> + /*
> + * If the limit is above the highmem start by less than the reserved
> + * size allocation in highmem won't be possible. Lower the limit to the
> + * lowmem end.
> + */
> + if (limit > highmem_start && limit - size < highmem_start)
> + limit = highmem_start;
> +
> +
How about removing this check?
Without this check, memblock_alloc_range would be failed and we can
go fallback correctly. So, this is redundant, IMO.
Thanks.
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