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Date: Mon, 13 May 2013 10:00:52 +0200
From: Maarten Lankhorst <maarten.lankhorst@canonical.com>
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To: Inki Dae <inki.dae@samsung.com>
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Subject: Re: Introduce a new helper framework for buffer synchronization
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Op 09-05-13 09:33, Inki Dae schreef:
> Hi all,
>
> This post introduces a new helper framework based on dma fence. And the
> purpose of this post is to collect other opinions and advices before RFC
> posting.
>
> First of all, this helper framework, called fence helper, is in progress
> yet so might not have enough comments in codes and also might need to be
> more cleaned up. Moreover, we might be missing some parts of the dma fence.
> However, I'd like to say that all things mentioned below has been tested
> with Linux platform and worked well.

> ....
>
> And tutorial for user process.
>         just before cpu access
>                 struct dma_buf_fence *df;
>
>                 df->type = DMA_BUF_ACCESS_READ or DMA_BUF_ACCESS_WRITE;
>                 ioctl(fd, DMA_BUF_GET_FENCE, &df);
>
>         after memset or memcpy
>                 ioctl(fd, DMA_BUF_PUT_FENCE, &df);
NAK.

Userspace doesn't need to trigger fences. It can do a buffer idle wait, and postpone submitting new commands until after it's done using the buffer.
Kernel space doesn't need the root hole you created by giving a dereferencing a pointer passed from userspace.
Your next exercise should be to write a security exploit from the api you created here. It's the only way to learn how to write safe code. Hint: df.ctx = mmap(..);

~Maarten