linux-kernel - Re: [PATCH v2 1/2] iommu/dma: Respect __GFP_DMA and __GFP

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Message-ID: <20170726091545.GC15833@8bytes.org>
Date:   Wed, 26 Jul 2017 11:15:46 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v2 1/2] iommu/dma: Respect __GFP_DMA and __GFP_DMA32 in
 incoming GFP flags

On Tue, Jul 04, 2017 at 10:55:55PM +0900, 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.
> 
> Signed-off-by: Tomasz Figa <tfiga@...omium.org>

Isn't it better to mask out __GFP_DMA and __GFP_DMA32 in the allocation
flags and only take them into account for iova allocation?

When the IOMMU re-maps the DMA to this memory it doesn't matter where it
is in system memory.



	Joerg