> -----Original Message----- > From: Maarten Lankhorst [mailto:maarten.lankhorst at canonical.com] > Sent: Monday, May 13, 2013 5:01 PM > To: Inki Dae > Cc: Rob Clark; Daniel Vetter; DRI mailing list; linux-arm- > kernel at lists.infradead.org; linux-media at vger.kernel.org; linux-fbdev; > Kyungmin Park; myungjoo.ham; YoungJun Cho > Subject: Re: Introduce a new helper framework for buffer synchronization > > 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.
Hi Maarten, It seems that you say user should wait for a buffer like KDS does: KDS uses select() to postpone submitting new commands. But I think this way assumes that every data flows a DMA device to a CPU. For example, a CPU should keep polling for the completion of a buffer access by a DMA device. This means that the this way isn't considered for data flow to opposite case; CPU to DMA device. > 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(..); > Also I'm not clear to use our way yet and that is why I posted. As you mentioned, it seems like that using mmap() is more safe. But there is one issue it makes me confusing. For your hint, df.ctx = mmap(..), the issue is that dmabuf mmap can be used to map a dmabuf with user space. And the dmabuf means a physical memory region allocated by some allocator such as drm gem or ion. There might be my missing point so could you please give me more comments? Thanks, Inki Dae > ~Maarten
