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

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Message-ID: <CANMq1KCHGZ2vEWg+OQQ-SwvHcU-oMp4qKzEYfLwRYD5ZmRdRsA@mail.gmail.com>
Date:   Thu, 22 Nov 2018 09:20:46 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     mhocko@...nel.org
Cc:     Will Deacon <will.deacon@....com>,
        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 Mailing List <linux-arm-kernel@...ts.infradead.org>,
        iommu@...ts.linux-foundation.org,
        lkml <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 Thu, Nov 22, 2018 at 2:02 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> 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?

GFP_DMA32 will fail due to check_slab_flags (aka GFP_SLAB_BUG_MASK
before patch 1/3 of this series)... But yes, it may be neater if there
was transparent remapping of GFP_DMA32/SLAB_CACHE_DMA32 to
GFP_DMA/SLAB_CACHE_DMA on 32-bit arch...

> --
> Michal Hocko
> SUSE Labs