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From: Catalin Marinas <catalin.marinas@arm.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>, Will Deacon <will@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	iommu@lists.linux-foundation.org,
	Rob Herring <robh+dt@kernel.org>,
	linux-rpi-kernel@lists.infradead.org,
	Frank Rowand <frowand.list@gmail.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 1/4] of/fdt: Update zone_dma_bits when running in bcm2711
Date: Mon, 12 Oct 2020 09:47:47 +0100	[thread overview]
Message-ID: <20201012084746.GA9844@gaia> (raw)
In-Reply-To: <20201012064715.GA2548@lst.de>

On Mon, Oct 12, 2020 at 08:47:15AM +0200, Christoph Hellwig wrote:
> On Fri, Oct 09, 2020 at 06:10:52PM +0100, Catalin Marinas wrote:
> > kdump wants DMA-able memory and,
> 
> DMAable by whom?  The only way to guranteed DMAable memory is to use
> the DMA memory allocator(s) and pass a specific device to them.  Everyting
> else is just fundamentally broken.  Note that even when device is not
> DMAable we can still use swiotlb to access it.

What I meant is that the new kexec'ed kernel needs some memory in the
ZONE_DMA range, currently set to the bottom 30-bit even for platforms
that can cope with the whole 32-bit range (anything other than RPi4).
The memory range available to the kdump kernels is limited to what
reserve_crashkernel() allocated, which may not fit in the lower 1GB.

There are two ongoing threads (complementary):

1. Change the arm64 reserve_crashkernel() similar to x86 which allocates
   memory above 4G with a small block in the ZONE_DMA range.

2. Allow zone_dma_bits to be 32 for arm64 platforms other than RPi4.

The second point also fixes some regressions with CMA reservations that
could no longer fit in the lower 1GB.

-- 
Catalin


  reply	other threads:[~2020-10-12  8:47 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-01 16:17 [PATCH 0/4] arm64: Default to 32-bit wide ZONE_DMA Nicolas Saenz Julienne
2020-10-01 16:17 ` [PATCH 1/4] of/fdt: Update zone_dma_bits when running in bcm2711 Nicolas Saenz Julienne
2020-10-01 17:15   ` Catalin Marinas
2020-10-01 17:23     ` Catalin Marinas
2020-10-01 17:31       ` Nicolas Saenz Julienne
2020-10-01 20:02         ` Rob Herring
2020-10-02 11:55         ` Catalin Marinas
2020-10-08 10:05           ` Nicolas Saenz Julienne
2020-10-08 10:13             ` Catalin Marinas
2020-10-08 19:43               ` Ard Biesheuvel
2020-10-09  3:59                 ` Jeremy Linton
2020-10-09  8:37                   ` Nicolas Saenz Julienne
2020-10-09  7:10             ` Christoph Hellwig
2020-10-09  7:37               ` Ard Biesheuvel
2020-10-09  8:36                 ` Nicolas Saenz Julienne
2020-10-09  9:13                   ` Ard Biesheuvel
2020-10-09 13:33                     ` Nicolas Saenz Julienne
2020-10-09 15:24                     ` Lorenzo Pieralisi
2020-10-09 16:23                       ` Ard Biesheuvel
2020-10-09 17:10                         ` Catalin Marinas
2020-10-10 10:36                           ` Ard Biesheuvel
2020-10-10 10:53                             ` Nicolas Saenz Julienne
2020-10-10 12:38                               ` Catalin Marinas
2020-10-12  6:47                           ` Christoph Hellwig
2020-10-12  8:47                             ` Catalin Marinas [this message]
2020-10-02  9:05   ` kernel test robot
2020-10-01 16:17 ` [PATCH 2/4] dma-direct: Turn zone_dma_bits default value into a define Nicolas Saenz Julienne
2020-10-01 16:17 ` [PATCH 3/4] arm64: Default to 32-bit ZONE_DMA Nicolas Saenz Julienne
2020-10-01 17:19   ` Catalin Marinas
2020-10-01 16:17 ` [PATCH 4/4] mm: Update DMA zones description Nicolas Saenz Julienne
2020-10-01 17:19   ` Catalin Marinas

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