linux-kernel - Re: [PATCH v2 3/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging

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Date:   Wed, 21 Nov 2018 19:02:20 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Nicolas Boichat <drinkcat@...omium.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Levin Alexander <Alexander.Levin@...rosoft.com>,
        Huaisheng Ye <yehs1@...ovo.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Yong Wu <yong.wu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Tomasz Figa <tfiga@...gle.com>, yingjoe.chen@...iatek.com
Subject: Re: [PATCH v2 3/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory,
 and improve debugging

On Wed 21-11-18 16:46:38, Will Deacon wrote:
> On Sun, Nov 11, 2018 at 05:03:41PM +0800, Nicolas Boichat wrote:
> > For level 1/2 pages, ensure GFP_DMA32 is used if CONFIG_ZONE_DMA32
> > is defined (e.g. on arm64 platforms).
> > 
> > For level 2 pages, allocate a slab cache in SLAB_CACHE_DMA32.
> > 
> > Also, print an error when the physical address does not fit in
> > 32-bit, to make debugging easier in the future.
> > 
> > Fixes: ad67f5a6545f ("arm64: replace ZONE_DMA with ZONE_DMA32")
> > Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
> > ---
> > 
> > Changes since v1:
> >  - Changed approach to use SLAB_CACHE_DMA32 added by the previous
> >    commit.
> >  - Use DMA or DMA32 depending on the architecture (DMA for arm,
> >    DMA32 for arm64).
> > 
> > drivers/iommu/io-pgtable-arm-v7s.c | 20 ++++++++++++++++----
> >  1 file changed, 16 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
> > index 445c3bde04800c..996f7b6d00b44a 100644
> > --- a/drivers/iommu/io-pgtable-arm-v7s.c
> > +++ b/drivers/iommu/io-pgtable-arm-v7s.c
> > @@ -161,6 +161,14 @@
> >  
> >  #define ARM_V7S_TCR_PD1			BIT(5)
> >  
> > +#ifdef CONFIG_ZONE_DMA32
> > +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA32
> > +#define ARM_V7S_TABLE_SLAB_CACHE SLAB_CACHE_DMA32
> > +#else
> > +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA
> > +#define ARM_V7S_TABLE_SLAB_CACHE SLAB_CACHE_DMA
> > +#endif
> 
> It's a bit grotty that GFP_DMA32 doesn't just map to GFP_DMA on 32-bit
> architectures, since then we wouldn't need this #ifdeffery afaict.

But GFP_DMA32 should map to GFP_KERNEL on 32b, no? Or what exactly is
going on in here?

-- 
Michal Hocko
SUSE Labs