From: Rob Herring <robh@kernel.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Grant Likely <grant.likely@arm.com>,
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Marek Szyprowski <m.szyprowski@samsung.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Saravana Kannan <saravanak@google.com>,
Heinrich Schuchardt <xypron.glpk@gmx.de>,
Joerg Roedel <joro@8bytes.org>,
"Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
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Juergen Gross <jgross@suse.com>,
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Tomasz Figa <tfiga@chromium.org>,
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linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Thiago Jung Bauermann <bauerman@linux.ibm.com>
Subject: Re: [RFC PATCH v3 5/6] dt-bindings: of: Add restricted DMA pool
Date: Wed, 20 Jan 2021 15:31:17 -0600 [thread overview]
Message-ID: <CAL_JsqKjTqcCbCLksRbCh7=f-A3Y09A3jNqtUApaA+p=RKd_Eg@mail.gmail.com> (raw)
In-Reply-To: <313f8052-a591-75de-c4c2-ee9ea8f02e7f@arm.com>
On Wed, Jan 20, 2021 at 11:30 AM Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 2021-01-20 16:53, Rob Herring wrote:
> > On Wed, Jan 06, 2021 at 11:41:23AM +0800, Claire Chang wrote:
> >> Introduce the new compatible string, restricted-dma-pool, for restricted
> >> DMA. One can specify the address and length of the restricted DMA memory
> >> region by restricted-dma-pool in the device tree.
> >
> > If this goes into DT, I think we should be able to use dma-ranges for
> > this purpose instead. Normally, 'dma-ranges' is for physical bus
> > restrictions, but there's no reason it can't be used for policy or to
> > express restrictions the firmware has enabled.
>
> There would still need to be some way to tell SWIOTLB to pick up the
> corresponding chunk of memory and to prevent the kernel from using it
> for anything else, though.
Don't we already have that problem if dma-ranges had a very small
range? We just get lucky because the restriction is generally much
more RAM than needed.
In any case, wouldn't finding all the dma-ranges do this? We're
already walking the tree to find the max DMA address now.
> >> Signed-off-by: Claire Chang <tientzu@chromium.org>
> >> ---
> >> .../reserved-memory/reserved-memory.txt | 24 +++++++++++++++++++
> >> 1 file changed, 24 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> >> index e8d3096d922c..44975e2a1fd2 100644
> >> --- a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> >> +++ b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> >> @@ -51,6 +51,20 @@ compatible (optional) - standard definition
> >> used as a shared pool of DMA buffers for a set of devices. It can
> >> be used by an operating system to instantiate the necessary pool
> >> management subsystem if necessary.
> >> + - restricted-dma-pool: This indicates a region of memory meant to be
> >> + used as a pool of restricted DMA buffers for a set of devices. The
> >> + memory region would be the only region accessible to those devices.
> >> + When using this, the no-map and reusable properties must not be set,
> >> + so the operating system can create a virtual mapping that will be used
> >> + for synchronization. The main purpose for restricted DMA is to
> >> + mitigate the lack of DMA access control on systems without an IOMMU,
> >> + which could result in the DMA accessing the system memory at
> >> + unexpected times and/or unexpected addresses, possibly leading to data
> >> + leakage or corruption. The feature on its own provides a basic level
> >> + of protection against the DMA overwriting buffer contents at
> >> + unexpected times. However, to protect against general data leakage and
> >> + system memory corruption, the system needs to provide way to restrict
> >> + the DMA to a predefined memory region.
> >> - vendor specific string in the form <vendor>,[<device>-]<usage>
> >> no-map (optional) - empty property
> >> - Indicates the operating system must not create a virtual mapping
> >> @@ -120,6 +134,11 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
> >> compatible = "acme,multimedia-memory";
> >> reg = <0x77000000 0x4000000>;
> >> };
> >> +
> >> + restricted_dma_mem_reserved: restricted_dma_mem_reserved {
> >> + compatible = "restricted-dma-pool";
> >> + reg = <0x50000000 0x400000>;
> >> + };
> >> };
> >>
> >> /* ... */
> >> @@ -138,4 +157,9 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
> >> memory-region = <&multimedia_reserved>;
> >> /* ... */
> >> };
> >> +
> >> + pcie_device: pcie_device@0,0 {
> >> + memory-region = <&restricted_dma_mem_reserved>;
> >
> > PCI hosts often have inbound window configurations that limit the
> > address range and translate PCI to bus addresses. Those windows happen
> > to be configured by dma-ranges. In any case, wouldn't you want to put
> > the configuration in the PCI host node? Is there a usecase of
> > restricting one PCIe device and not another?
>
> The general design seems to accommodate devices having their own pools
> such that they can't even snoop on each others' transient DMA data. If
> the interconnect had a way of wiring up, say, PCI RIDs to AMBA NSAIDs,
> then in principle you could certainly apply that to PCI endpoints too
> (presumably you'd also disallow them from peer-to-peer transactions at
> the PCI level too).
At least for PCI, I think we can handle this. We have the BDF in the
3rd address cell in dma-ranges. The Openfirmware spec says those are 0
in the case of ranges. It doesn't talk about dma-ranges though. But I
think we could extend it to allow for BDF. Though typically with PCIe
every device is behind its own bridge and each bridge node can have a
dma-ranges.
Rob
next prev parent reply other threads:[~2021-01-20 21:33 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-06 3:41 [RFC PATCH v3 0/6] Restricted DMA Claire Chang
2021-01-06 3:41 ` [RFC PATCH v3 1/6] swiotlb: Add io_tlb_mem struct Claire Chang
2021-01-13 11:50 ` Christoph Hellwig
2021-01-06 3:41 ` [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool Claire Chang
2021-01-06 7:50 ` Greg KH
2021-01-13 11:51 ` Christoph Hellwig
2021-01-13 12:29 ` Greg KH
2021-01-13 12:37 ` Christoph Hellwig
2021-01-06 18:52 ` Konrad Rzeszutek Wilk
2021-01-07 17:39 ` Claire Chang
2021-01-07 17:57 ` Konrad Rzeszutek Wilk
2021-01-07 18:09 ` Florian Fainelli
2021-01-07 21:19 ` Konrad Rzeszutek Wilk
2021-01-12 23:52 ` Florian Fainelli
2021-01-25 5:26 ` Jon Masters
2021-01-13 1:53 ` Robin Murphy
2021-01-13 0:03 ` Florian Fainelli
2021-01-13 13:59 ` Nicolas Saenz Julienne
2021-01-13 15:27 ` Robin Murphy
2021-01-13 17:43 ` Florian Fainelli
2021-01-13 18:03 ` Robin Murphy
2021-01-13 12:42 ` Christoph Hellwig
2021-01-14 9:06 ` Claire Chang
2021-01-06 3:41 ` [RFC PATCH v3 3/6] swiotlb: Use restricted DMA pool if available Claire Chang
2021-01-12 23:39 ` Florian Fainelli
2021-01-13 12:44 ` Christoph Hellwig
2021-01-06 3:41 ` [RFC PATCH v3 4/6] swiotlb: Add restricted DMA alloc/free support Claire Chang
2021-01-12 23:41 ` Florian Fainelli
2021-01-13 12:48 ` Christoph Hellwig
2021-01-13 18:27 ` Robin Murphy
2021-01-13 18:32 ` Christoph Hellwig
2021-01-06 3:41 ` [RFC PATCH v3 5/6] dt-bindings: of: Add restricted DMA pool Claire Chang
2021-01-06 18:57 ` Konrad Rzeszutek Wilk
2021-01-07 17:39 ` Claire Chang
2021-01-07 18:00 ` Konrad Rzeszutek Wilk
2021-01-07 18:14 ` Florian Fainelli
2021-01-12 7:47 ` Claire Chang
2021-01-20 16:53 ` Rob Herring
2021-01-20 17:30 ` Robin Murphy
2021-01-20 21:31 ` Rob Herring [this message]
2021-01-21 1:09 ` Robin Murphy
2021-01-21 15:48 ` Rob Herring
2021-01-21 17:29 ` Robin Murphy
2021-01-06 3:41 ` [RFC PATCH v3 6/6] of: Add plumbing for " Claire Chang
2021-01-12 23:48 ` Florian Fainelli
2021-01-14 9:08 ` Claire Chang
2021-01-14 18:52 ` Florian Fainelli
2021-01-15 3:46 ` Claire Chang
2021-01-06 18:48 ` [RFC PATCH v3 0/6] Restricted DMA Florian Fainelli
2021-01-07 17:38 ` Claire Chang
2021-01-07 17:42 ` Claire Chang
2021-01-07 17:59 ` Florian Fainelli
2021-01-12 7:48 ` Claire Chang
2021-01-12 18:01 ` Florian Fainelli
2021-01-13 2:29 ` Tomasz Figa
2021-01-13 3:56 ` Florian Fainelli
2021-01-13 4:25 ` Tomasz Figa
2021-01-13 4:41 ` Florian Fainelli
2021-02-09 6:27 ` Claire Chang
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