Re: [PATCH 1/1] drivers: dma-contiguous: Ensure cma reserve region never cross the low/high mem boundary

[Laura Abbott]

On 11/16/2016 06:19 AM, Jason Liu wrote:
> If the cma reserve region goes through the device-tree method,
> also need ensure the cma reserved region not cross the low/high
> mem boundary. This patch did the similar fix as commit:16195dd
> ("mm: cma: Ensure that reservations never cross the low/high mem boundary")
> 
> Signed-off-by: Jason Liu <jason.hui.liu@xxxxxxx>
> Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/base/dma-contiguous.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/base/dma-contiguous.c b/drivers/base/dma-contiguous.c
> index e167a1e1..2bc093c 100644
> --- a/drivers/base/dma-contiguous.c
> +++ b/drivers/base/dma-contiguous.c
> @@ -244,6 +244,7 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
>  {
>  	phys_addr_t align = PAGE_SIZE << max(MAX_ORDER - 1, pageblock_order);
>  	phys_addr_t mask = align - 1;
> +	phys_addr_t highmem_start;
>  	unsigned long node = rmem->fdt_node;
>  	struct cma *cma;
>  	int err;
> @@ -256,6 +257,32 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
>  		pr_err("Reserved memory: incorrect alignment of CMA region\n");
>  		return -EINVAL;
>  	}
> +#ifdef CONFIG_X86
> +	/*
> +	 * high_memory isn't direct mapped memory so retrieving its physical
> +	 * address isn't appropriate.  But it would be useful to check the
> +	 * physical address of the highmem boundary so it's justfiable to get
> +	 * the physical address from it.  On x86 there is a validation check for
> +	 * this case, so the following workaround is needed to avoid it.
> +	 */
> +	highmem_start = __pa_nodebug(high_memory);
> +#else
> +	highmem_start = __pa(high_memory);
> +#endif

The inline #ifdef is not great style, we shouldn't be spreading it around.

> +
> +	/*
> +	 * All pages in the reserved area must come from the same zone.
> +	 * If the reserved region crosses the low/high memory boundary,
> +	 * try to fix it up and then fall back to allocate from the low mem
> +	 */
> +	if (rmem->base < highmem_start &&
> +		(rmem->base + rmem->size) > highmem_start) {
> +		memblock_free(rmem->base, rmem->size);
> +		rmem->base = memblock_alloc_range(rmem->size, align, 0,
> +						highmem_start, MEMBLOCK_NONE);
> +		if (!rmem->base)
> +			return -ENOMEM;
> +	}

Given the alloc happened in the of code, it seems bad form to be
bringing the free and re-alloc here. Perhaps we should be doing the
limiting and checking in the reserved mem code?

If there is no other solution, at the least this deserves a pr_warn
so users know why a reason specified may not be getting requested.

>  
>  	err = cma_init_reserved_mem(rmem->base, rmem->size, 0, &cma);
>  	if (err) {
> 


Thanks,
Laura