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Message-ID: <e39e8f87ed5b4e9da2f08a0651801954e61f4b4e.camel@suse.de>
Subject: Re: [PATCH] dma-pool: Do not allocate pool memory from CMA
From:   Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Amit Pundir <amit.pundir@linaro.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        David Rientjes <rientjes@google.com>,
        linux-rpi-kernel@lists.infradead.org, jeremy.linton@arm.com,
        iommu@lists.linux-foundation.org,
        lkml <linux-kernel@vger.kernel.org>,
        John Stultz <john.stultz@linaro.org>,
        Sumit Semwal <sumit.semwal@linaro.org>
Date:   Tue, 28 Jul 2020 11:30:32 +0200
In-Reply-To: <20200728091335.GA23744@lst.de>
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On Tue, 2020-07-28 at 11:13 +0200, Christoph Hellwig wrote:
> On Mon, Jul 27, 2020 at 07:56:56PM +0200, Nicolas Saenz Julienne wrote:
> > Hi Christoph,
> > thanks for having a look at this!
> >=20
> > On Fri, 2020-07-24 at 15:41 +0200, Christoph Hellwig wrote:
> > > Yes, the iommu is an interesting case, and the current code is
> > > wrong for that.
> >=20
> > Care to expand on this? I do get that checking dma_coherent_ok() on mem=
ory
> > that'll later on be mapped into an iommu is kind of silly, although I t=
hink
> > harmless in Amir's specific case, since devices have wide enough dma-
ranges.=20
> > Is
> > there more to it?
>=20
> I think the problem is that it can lead to not finding suitable memory.
>=20
> > > Can you try the patch below?  It contains a modified version of Nicol=
as'
> > > patch to try CMA again for the expansion and a new (for now hackish) =
way
> > > to
> > > not apply the addressability check for dma-iommu allocations.
> > >=20
> > > diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> > > index 6bc74a2d51273e..ec5e525d2b9309 100644
> > > --- a/kernel/dma/pool.c
> > > +++ b/kernel/dma/pool.c
> > > @@ -3,7 +3,9 @@
> > >   * Copyright (C) 2012 ARM Ltd.
> > >   * Copyright (C) 2020 Google LLC
> > >   */
> > > +#include <linux/cma.h>
> > >  #include <linux/debugfs.h>
> > > +#include <linux/dma-contiguous.h>
> > >  #include <linux/dma-direct.h>
> > >  #include <linux/dma-noncoherent.h>
> > >  #include <linux/init.h>
> > > @@ -55,6 +57,31 @@ static void dma_atomic_pool_size_add(gfp_t gfp, si=
ze_t
> > > size)
> > >  		pool_size_kernel +=3D size;
> > >  }
> > > =20
> > > +static bool cma_in_zone(gfp_t gfp)
> > > +{
> > > +	phys_addr_t end;
> > > +	unsigned long size;
> > > +	struct cma *cma;
> > > +
> > > +	cma =3D dev_get_cma_area(NULL);
> > > +	if (!cma)
> > > +		return false;
> > > +
> > > +	size =3D cma_get_size(cma);
> > > +	if (!size)
> > > +		return false;
> > > +	end =3D cma_get_base(cma) - memblock_start_of_DRAM() + size - 1;
> > > +
> > > +	/* CMA can't cross zone boundaries, see cma_activate_area() */
> > > +	if (IS_ENABLED(CONFIG_ZONE_DMA) && (gfp & GFP_DMA) &&
> > > +	    end <=3D DMA_BIT_MASK(zone_dma_bits))
> > > +		return true;
> > > +	if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp & GFP_DMA32) &&
> > > +	    end <=3D DMA_BIT_MASK(32))
> > > +		return true;
> > > +	return true;
> >=20
> > IIUC this will always return true given a CMA is present. Which reverts=
 to
> > the
> > previous behaviour (previous as in breaking some rpi4 setups), isn't it=
?
>=20
> Was that really what broke the PI?  I'll try to get the split out series
> today, which might have a few more tweaks, and then we'll need to test it
> both on these rpi4 setups and Amits phone.

There was two issues with RPi:
 - Not validating that pool allocated memory was OK for the device
 - Locating all atomic pools in CMA, which doesn't work for all RPi4 device=
s*,
   and IMO misses the point of having multiple pools.

* With ACPI RPi4 we have CMA located in ZONE_DMA32, yet have an atomic pool
consumer, PCIe, that only wants memory in the [0 3GB] area, effectively nee=
ding
ZONE_DMA memory.


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