linux-kernel - Re: [PATCH 1/2] iommu/dma: Respect __GFP_DMA and __GFP

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Date:   Tue, 27 Jun 2017 12:01:21 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Tomasz Figa <tfiga@...omium.org>, iommu@...ts.linux-foundation.org
Cc:     linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH 1/2] iommu/dma: Respect __GFP_DMA and __GFP_DMA32 in
 incoming GFP flags

On 27/06/17 08:28, Tomasz Figa wrote:
> Current implementation of __iommu_dma_alloc_pages() keeps adding
> __GFP_HIGHMEM to GFP flags regardless of whether other zone flags are
> already included in the incoming flags. If __GFP_DMA or __GFP_DMA32 is
> set at the same time as __GFP_HIGHMEM, the allocation fails due to
> invalid zone flag combination.
> 
> Fix this by checking for __GFP_DMA and __GFP_DMA32 in incoming GFP flags
> and adding __GFP_HIGHMEM only if they are not present.

Wouldn't it make more sense to strip off the ZONE_DMA* related flags,
since the whole point here is that we don't care where the pages come from?

Robin.

> Signed-off-by: Tomasz Figa <tfiga@...omium.org>
> ---
>  drivers/iommu/dma-iommu.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 9d1cebe7f6cb..29965a092a69 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -445,8 +445,14 @@ static struct page **__iommu_dma_alloc_pages(unsigned int count,
>  	if (!pages)
>  		return NULL;
>  
> -	/* IOMMU can map any pages, so himem can also be used here */
> -	gfp |= __GFP_NOWARN | __GFP_HIGHMEM;
> +	/*
> +	 * IOMMU can map any pages, so himem can also be used here,
> +	 * unless another DMA zone is explicitly requested.
> +	 */
> +	if (!(gfp & (__GFP_DMA | __GFP_DMA32)))
> +		gfp |= __GFP_HIGHMEM;
> +
> +	gfp |= __GFP_NOWARN;
>  
>  	while (count) {
>  		struct page *page = NULL;
>