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Subject: Re: DMA Engine: Transfer From Userspace
To:     Vinod Koul <vkoul@kernel.org>
Cc:     Federico Vaga <federico.vaga@cern.ch>,
        Dan Williams <dan.j.williams@intel.com>,
        dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
        "Luck, Tony" <tony.luck@intel.com>
References: <5614531.lOV4Wx5bFT@harkonnen>
 <fe199e18-be45-cadc-8bad-4a83ed87bfba@intel.com>
 <20200621072457.GA2324254@vkoul-mobl>
From:   Dave Jiang <dave.jiang@intel.com>
Message-ID: <581f1761-e582-c770-169a-ee3374baf25c@intel.com>
Date:   Wed, 24 Jun 2020 17:42:24 -0700
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On 6/21/2020 12:24 AM, Vinod Koul wrote:
> On 19-06-20, 16:31, Dave Jiang wrote:
>>
>>
>> On 6/19/2020 3:47 PM, Federico Vaga wrote:
>>> Hello,
>>>
>>> is there the possibility of using a DMA engine channel from userspace?
>>>
>>> Something like:
>>> - configure DMA using ioctl() (or whatever configuration mechanism)
>>> - read() or write() to trigger the transfer
>>>
>>
>> I may have supposedly promised Vinod to look into possibly providing
>> something like this in the future. But I have not gotten around to do that
>> yet. Currently, no such support.
> 
> And I do still have serious reservations about this topic :) Opening up
> userspace access to DMA does not sound very great from security point of
> view.

What about doing it with DMA engine that supports PASID? That way the user can 
really only trash its own address space and kernel is protected.


> 
> Federico, what use case do you have in mind?
> 
> We should keep in mind dmaengine is an in-kernel interface providing
> services to various subsystems, so you go thru the respective subsystem
> kernel interface (network, display, spi, audio etc..) which would in
> turn use dmaengine.
>