linux-kernel - Re: [PATCH 12/21] dma-iommu: factor atomic pool allocations into helpers

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Date:   Tue, 9 Apr 2019 18:59:32 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     Joerg Roedel <joro@...tes.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/21] dma-iommu: factor atomic pool allocations into
 helpers

On 27/03/2019 08:04, Christoph Hellwig wrote:
> This keeps the code together and will simplify compiling the code
> out on architectures that are always dma coherent.

And this is where things take a turn in the direction I just can't get 
on with - I'm looking at the final result and the twisty maze of little 
disjoint helpers all overlapping each other in functionality is really 
difficult to follow. And I would *much* rather have things rely on 
compile-time constant optimisation than spend the future having to fix 
the #ifdefed parts for arm64 whenever x86-centric changes fail to test them.

Conceptually, everything except the iommu_dma_alloc_remap() case is more 
or less just dma_direct_alloc() with an IOMMU mapping on top - if we 
could pass that an internal flag to say "don't fail or bounce because of 
masks" it seems like that approach could end up being quite a bit 
simpler (I did once have lofty plans to refactor the old arm64 code in 
such a way...)

Robin.

> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   drivers/iommu/dma-iommu.c | 51 +++++++++++++++++++++++++++++----------
>   1 file changed, 38 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 2013c650718a..8ec69176673d 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -673,6 +673,35 @@ static int iommu_dma_get_sgtable_remap(struct sg_table *sgt, void *cpu_addr,
>   			GFP_KERNEL);
>   }
>   
> +static void iommu_dma_free_pool(struct device *dev, size_t size,
> +		void *vaddr, dma_addr_t dma_handle)
> +{
> +	__iommu_dma_unmap(iommu_get_domain_for_dev(dev), dma_handle, size);
> +	dma_free_from_pool(vaddr, PAGE_ALIGN(size));
> +}
> +
> +static void *iommu_dma_alloc_pool(struct device *dev, size_t size,
> +		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
> +{
> +	bool coherent = dev_is_dma_coherent(dev);
> +	struct page *page;
> +	void *vaddr;
> +
> +	vaddr = dma_alloc_from_pool(PAGE_ALIGN(size), &page, gfp);
> +	if (!vaddr)
> +		return NULL;
> +
> +	*dma_handle = __iommu_dma_map(dev, page_to_phys(page), size,
> +			dma_info_to_prot(DMA_BIDIRECTIONAL, coherent, attrs),
> +			iommu_get_domain_for_dev(dev));
> +	if (*dma_handle == DMA_MAPPING_ERROR) {
> +		dma_free_from_pool(vaddr, PAGE_ALIGN(size));
> +		return NULL;
> +	}
> +
> +	return vaddr;
> +}
> +
>   static void iommu_dma_sync_single_for_cpu(struct device *dev,
>   		dma_addr_t dma_handle, size_t size, enum dma_data_direction dir)
>   {
> @@ -981,21 +1010,18 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
>   		 * get the virtually contiguous buffer we need by way of a
>   		 * physically contiguous allocation.
>   		 */
> -		if (coherent) {
> -			page = alloc_pages(gfp, get_order(size));
> -			addr = page ? page_address(page) : NULL;
> -		} else {
> -			addr = dma_alloc_from_pool(size, &page, gfp);
> -		}
> -		if (!addr)
> +		if (!coherent)
> +			return iommu_dma_alloc_pool(dev, iosize, handle, gfp,
> +					attrs);
> +
> +		page = alloc_pages(gfp, get_order(size));
> +		if (!page)
>   			return NULL;
>   
> +		addr = page_address(page);
>   		*handle = __iommu_dma_map_page(dev, page, 0, iosize, ioprot);
>   		if (*handle == DMA_MAPPING_ERROR) {
> -			if (coherent)
> -				__free_pages(page, get_order(size));
> -			else
> -				dma_free_from_pool(addr, size);
> +			__free_pages(page, get_order(size));
>   			addr = NULL;
>   		}
>   	} else if (attrs & DMA_ATTR_FORCE_CONTIGUOUS) {
> @@ -1049,8 +1075,7 @@ static void iommu_dma_free(struct device *dev, size_t size, void *cpu_addr,
>   	 * Hence how dodgy the below logic looks...
>   	 */
>   	if (dma_in_atomic_pool(cpu_addr, size)) {
> -		__iommu_dma_unmap_page(dev, handle, iosize, 0, 0);
> -		dma_free_from_pool(cpu_addr, size);
> +		iommu_dma_free_pool(dev, size, cpu_addr, handle);
>   	} else if (attrs & DMA_ATTR_FORCE_CONTIGUOUS) {
>   		struct page *page = vmalloc_to_page(cpu_addr);
>   
>