Re: [PATCH] dma-pool: Only allocate from CMA when in same memory zone

[Nicolas Saenz Julienne]

Hi Chritoph,

On Fri, 2020-07-10 at 16:10 +0200, Nicolas Saenz Julienne wrote:
> There is no guarantee to CMA's placement, so allocating a zone specific
> atomic pool from CMA might return memory from a completely different
> memory zone. To get around this double check CMA's placement before
> allocating from it.
> 
> Fixes: c84dc6e68a1d ("dma-pool: add additional coherent pools to map to gfp
> mask")
> Reported-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> ---
> 
> This is a code intensive alternative to "dma-pool: Do not allocate pool
> memory from CMA"[1].

I see you applied "dma-pool: Do not allocate pool memory from CMA" on your
tree. Do you want me to send a v2 of this patch taking that into account
targeting v5.9? or you'd rather just follow another approach?

Regards,
Nicolas

> 
> [1] https://lkml.org/lkml/2020/7/8/1108
> 
>  kernel/dma/pool.c | 36 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 35 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> index 8cfa01243ed2..ccf3eeb77e00 100644
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -3,6 +3,7 @@
>   * Copyright (C) 2012 ARM Ltd.
>   * Copyright (C) 2020 Google LLC
>   */
> +#include <linux/cma.h>
>  #include <linux/debugfs.h>
>  #include <linux/dma-direct.h>
>  #include <linux/dma-noncoherent.h>
> @@ -56,6 +57,39 @@ static void dma_atomic_pool_size_add(gfp_t gfp, size_t
> size)
>  		pool_size_kernel += size;
>  }
>  
> +static bool cma_in_zone(gfp_t gfp)
> +{
> +	u64 zone_dma_end, zone_dma32_end;
> +	phys_addr_t base, end;
> +	unsigned long size;
> +	struct cma *cma;
> +
> +	cma = dev_get_cma_area(NULL);
> +	if (!cma)
> +		return false;
> +
> +	size = cma_get_size(cma);
> +	if (!size)
> +		return false;
> +	base = cma_get_base(cma) - memblock_start_of_DRAM();
> +	end = base + size - 1;
> +
> +	zone_dma_end = IS_ENABLED(CONFIG_ZONE_DMA) ? DMA_BIT_MASK(zone_dma_bits)
> : 0;
> +	zone_dma32_end = IS_ENABLED(CONFIG_ZONE_DMA32) ? DMA_BIT_MASK(32) : 0;
> +
> +	/* CMA can't cross zone boundaries, see cma_activate_area() */
> +	if (IS_ENABLED(CONFIG_ZONE_DMA) && gfp & GFP_DMA &&
> +	   end <= zone_dma_end)
> +		return true;
> +	else if (IS_ENABLED(CONFIG_ZONE_DMA32) && gfp & GFP_DMA32 &&
> +		base > zone_dma_end && end <= zone_dma32_end)
> +		return true;
> +	else if (base > zone_dma32_end)
> +		return true;
> +
> +	return false;
> +}
> +
>  static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
>  			      gfp_t gfp)
>  {
> @@ -70,7 +104,7 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t
> pool_size,
>  	do {
>  		pool_size = 1 << (PAGE_SHIFT + order);
>  
> -		if (dev_get_cma_area(NULL))
> +		if (cma_in_zone(gfp))
>  			page = dma_alloc_from_contiguous(NULL, 1 << order,
>  							 order, false);
>  		else

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