From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Claire Chang <tientzu@chromium.org>
Cc: heikki.krogerus@linux.intel.com, peterz@infradead.org,
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"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
Joerg Roedel <joro@8bytes.org>,
" <iommu@lists.linux-foundation.org>,
xypron.glpk@gmx.de, Robin Murphy <robin.murphy@arm.com>
Subject: Re: [RFC PATCH v3 5/6] dt-bindings: of: Add restricted DMA pool
Date: Thu, 7 Jan 2021 13:00:32 -0500 [thread overview]
Message-ID: <20210107180032.GB16519@char.us.oracle.com> (raw)
In-Reply-To: <CALiNf2_dV13jbHqLt-r1eK+dtOcAKBGcWQCVMQn+eL6MuOrETQ@mail.gmail.com>
On Fri, Jan 08, 2021 at 01:39:43AM +0800, Claire Chang wrote:
> On Thu, Jan 7, 2021 at 2:58 AM Konrad Rzeszutek Wilk
> <konrad.wilk@oracle.com> 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.
> > >
> > > 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.
> >
> > Heya!
> >
> > I think I am missing something obvious here so please bear with my
> > questions:
> >
> > - This code adds the means of having the SWIOTLB pool tied to a specific
> > memory correct?
>
> It doesn't affect the existing SWIOTLB. It just utilizes the existing SWIOTLB
> code to create another DMA pool tied to a specific memory region for a given set
> of devices. It bounces the streaming DMA (map/unmap) in and out of that region
> and does the memory allocation (dma_direct_alloc) from the same region.
Right, so why can't it follow the same mechanism that Xen SWIOTLB does - which
had exactly the same problem (needed special handling on the pool) - and do
a similar code?
>
> >
> >
> > - Nothing stops the physical device from bypassing the SWIOTLB buffer.
> > That is if an errant device screwed up the length or DMA address, the
> > SWIOTLB would gladly do what the device told it do?
>
> So the system needs to provide a way to lock down the memory access, e.g. MPU.
OK! Would it be prudent to have this in the description above perhaps?
>
> >
> > - This has to be combined with SWIOTLB-force-ish to always use the
> > bounce buffer, otherwise you could still do DMA without using
> > SWIOTLB (by not hitting the criteria for needing to use SWIOTLB)?
>
> Since restricted DMA is for the devices that are not behind an IOMMU, I change
> the criteria
> `if (unlikely(swiotlb_force == SWIOTLB_FORCE))`
> to
> `if (unlikely(swiotlb_force == SWIOTLB_FORCE) || dev->dma_io_tlb_mem)`
> in dma_direct_map_page().
>
> Also, even if SWIOTLB=force, the restricted DMA pool is preferred if available
> (get_io_tlb_mem in https://lore.kernel.org/patchwork/patch/1360995/).
>
> Thanks!
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next prev parent reply other threads:[~2021-01-07 18:04 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 [this message]
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
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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