From: Christoph Hellwig <hch@lst.de>
To: Alexander Graf <graf@amazon.com>
Cc: iommu@lists.linux-foundation.org,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
x86@kernel.org, Christoph Hellwig <hch@lst.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
Mark Rutland <mark.rutland@arm.com>,
dwmw@amazon.com, benh@amazon.com,
Jan Kiszka <jan.kiszka@siemens.com>,
alcioa@amazon.com, aggh@amazon.com, aagch@amazon.com,
dhr@amazon.com
Subject: Re: [PATCH] swiotlb: Allow swiotlb to live at pre-defined address
Date: Thu, 26 Mar 2020 18:05:16 +0100 [thread overview]
Message-ID: <20200326170516.GB6387@lst.de> (raw)
In-Reply-To: <20200326162922.27085-1-graf@amazon.com>
On Thu, Mar 26, 2020 at 05:29:22PM +0100, Alexander Graf wrote:
> The swiotlb is a very convenient fallback mechanism for bounce buffering of
> DMAable data. It is usually used for the compatibility case where devices
> can only DMA to a "low region".
>
> However, in some scenarios this "low region" may be bound even more
> heavily. For example, there are embedded system where only an SRAM region
> is shared between device and CPU. There are also heterogeneous computing
> scenarios where only a subset of RAM is cache coherent between the
> components of the system. There are partitioning hypervisors, where
> a "control VM" that implements device emulation has limited view into a
> partition's memory for DMA capabilities due to safety concerns.
>
> This patch adds a command line driven mechanism to move all DMA memory into
> a predefined shared memory region which may or may not be part of the
> physical address layout of the Operating System.
>
> Ideally, the typical path to set this configuration would be through Device
> Tree or ACPI, but neither of the two mechanisms is standardized yet. Also,
> in the x86 MicroVM use case, we have neither ACPI nor Device Tree, but
> instead configure the system purely through kernel command line options.
>
> I'm sure other people will find the functionality useful going forward
> though and extend it to be triggered by DT/ACPI in the future.
I'm totally against hacking in a kernel parameter for this. We'll need
a proper documented DT or ACPI way. We also need to feed this information
into the actual DMA bounce buffering decisions and not just the swiotlb
placement.
next prev parent reply other threads:[~2020-03-26 17:05 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-26 16:29 [PATCH] swiotlb: Allow swiotlb to live at pre-defined address Alexander Graf
2020-03-26 17:05 ` Christoph Hellwig [this message]
2020-03-26 17:11 ` Alexander Graf
2020-03-26 17:16 ` David Woodhouse
2020-03-30 13:24 ` Mark Rutland
2020-03-27 6:05 ` kbuild test robot
2020-03-27 9:58 ` Jan Kiszka
2020-03-28 11:57 ` Dave Young
2020-03-30 6:06 ` Kairui Song
2020-03-30 13:40 ` Konrad Rzeszutek Wilk
2020-03-30 20:42 ` Alexander Graf
2020-03-30 23:37 ` Anthony Yznaga
2020-03-31 1:59 ` Dave Young
2020-03-31 2:16 ` Baoquan He
2020-03-31 1:46 ` Dave Young
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