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Subject: Re: [PATCH] dma-pool: use single atomic pool for both DMA zones
To:     Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        David Rientjes <rientjes@google.com>
Cc:     linux-rpi-kernel@lists.infradead.org,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
References: <20200707122804.21262-1-nsaenzjulienne@suse.de>
From:   Jeremy Linton <jeremy.linton@arm.com>
Message-ID: <3ee7f5ec-46e3-6d36-820b-011e359e759d@arm.com>
Date:   Wed, 8 Jul 2020 18:16:19 -0500
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Hi,

On 7/7/20 7:28 AM, Nicolas Saenz Julienne wrote:
> When allocating atomic DMA memory for a device, the dma-pool core
> queries __dma_direct_optimal_gfp_mask() to check which atomic pool to
> use. It turns out the GFP flag returned is only an optimistic guess.
> The pool selected might sometimes live in a zone higher than the
> device's view of memory.
> 
> As there isn't a way to grantee a mapping between a device's DMA
> constraints and correct GFP flags this unifies both DMA atomic pools.
> The resulting pool is allocated in the lower DMA zone available, if any,
> so as for devices to always get accessible memory while having the
> flexibility of using dma_pool_kernel for the non constrained ones.

With the follow-on patch "dma-pool: Do not allocate pool memory from 
CMA" everything seems to be working fine now.

tested-by: Jeremy Linton <jeremy.linton@arm.com>

Thanks for fixing this!


> 
> Fixes: c84dc6e68a1d ("dma-pool: add additional coherent pools to map to gfp mask")
> Reported-by: Jeremy Linton <jeremy.linton@arm.com>
> Suggested-by: Robin Murphy <robin.murphy@arm.com>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> ---
>   kernel/dma/pool.c | 47 +++++++++++++++++++----------------------------
>   1 file changed, 19 insertions(+), 28 deletions(-)
> 
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> index 8cfa01243ed2..883f7a583969 100644
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -13,10 +13,11 @@
>   #include <linux/slab.h>
>   #include <linux/workqueue.h>
>   
> +#define GFP_ATOMIC_POOL_DMA	(IS_ENABLED(CONFIG_ZONE_DMA) ? GFP_DMA : \
> +				 IS_ENABLED(CONFIG_ZONE_DMA32) ? GFP_DMA32 : 0)
> +
>   static struct gen_pool *atomic_pool_dma __ro_after_init;
>   static unsigned long pool_size_dma;
> -static struct gen_pool *atomic_pool_dma32 __ro_after_init;
> -static unsigned long pool_size_dma32;
>   static struct gen_pool *atomic_pool_kernel __ro_after_init;
>   static unsigned long pool_size_kernel;
>   
> @@ -42,16 +43,13 @@ static void __init dma_atomic_pool_debugfs_init(void)
>   		return;
>   
>   	debugfs_create_ulong("pool_size_dma", 0400, root, &pool_size_dma);
> -	debugfs_create_ulong("pool_size_dma32", 0400, root, &pool_size_dma32);
>   	debugfs_create_ulong("pool_size_kernel", 0400, root, &pool_size_kernel);
>   }
>   
>   static void dma_atomic_pool_size_add(gfp_t gfp, size_t size)
>   {
> -	if (gfp & __GFP_DMA)
> +	if (gfp & GFP_ATOMIC_POOL_DMA)
>   		pool_size_dma += size;
> -	else if (gfp & __GFP_DMA32)
> -		pool_size_dma32 += size;
>   	else
>   		pool_size_kernel += size;
>   }
> @@ -132,12 +130,11 @@ static void atomic_pool_resize(struct gen_pool *pool, gfp_t gfp)
>   
>   static void atomic_pool_work_fn(struct work_struct *work)
>   {
> -	if (IS_ENABLED(CONFIG_ZONE_DMA))
> -		atomic_pool_resize(atomic_pool_dma,
> -				   GFP_KERNEL | GFP_DMA);
> -	if (IS_ENABLED(CONFIG_ZONE_DMA32))
> -		atomic_pool_resize(atomic_pool_dma32,
> -				   GFP_KERNEL | GFP_DMA32);
> +	gfp_t dma_gfp = GFP_ATOMIC_POOL_DMA;
> +
> +	if (dma_gfp)
> +		atomic_pool_resize(atomic_pool_dma, GFP_KERNEL | dma_gfp);
> +
>   	atomic_pool_resize(atomic_pool_kernel, GFP_KERNEL);
>   }
>   
> @@ -168,6 +165,7 @@ static __init struct gen_pool *__dma_atomic_pool_init(size_t pool_size,
>   
>   static int __init dma_atomic_pool_init(void)
>   {
> +	gfp_t dma_gfp = GFP_ATOMIC_POOL_DMA;
>   	int ret = 0;
>   
>   	/*
> @@ -185,18 +183,13 @@ static int __init dma_atomic_pool_init(void)
>   						    GFP_KERNEL);
>   	if (!atomic_pool_kernel)
>   		ret = -ENOMEM;
> -	if (IS_ENABLED(CONFIG_ZONE_DMA)) {
> +
> +	if (dma_gfp) {
>   		atomic_pool_dma = __dma_atomic_pool_init(atomic_pool_size,
> -						GFP_KERNEL | GFP_DMA);
> +							 GFP_KERNEL | dma_gfp);
>   		if (!atomic_pool_dma)
>   			ret = -ENOMEM;
>   	}
> -	if (IS_ENABLED(CONFIG_ZONE_DMA32)) {
> -		atomic_pool_dma32 = __dma_atomic_pool_init(atomic_pool_size,
> -						GFP_KERNEL | GFP_DMA32);
> -		if (!atomic_pool_dma32)
> -			ret = -ENOMEM;
> -	}
>   
>   	dma_atomic_pool_debugfs_init();
>   	return ret;
> @@ -206,14 +199,12 @@ postcore_initcall(dma_atomic_pool_init);
>   static inline struct gen_pool *dev_to_pool(struct device *dev)
>   {
>   	u64 phys_mask;
> -	gfp_t gfp;
> -
> -	gfp = dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
> -					  &phys_mask);
> -	if (IS_ENABLED(CONFIG_ZONE_DMA) && gfp == GFP_DMA)
> -		return atomic_pool_dma;
> -	if (IS_ENABLED(CONFIG_ZONE_DMA32) && gfp == GFP_DMA32)
> -		return atomic_pool_dma32;
> +
> +	if (atomic_pool_dma &&
> +	    dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
> +					&phys_mask))
> +			return atomic_pool_dma;
> +
>   	return atomic_pool_kernel;
>   }
>   
>