Messages in this thread |  | | From | Simon Que <> | Date | Tue, 03 Apr 2018 01:27:36 +0000 | Subject | Looking for way to program external MMU from userspace (or viable alternative) |
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Hi kernel community,
We have an external PCIe board with a custom coprocessor on it. We also have code for a kernel driver for it. We have thought about upstreaming it, but we realized that we can instead convert the driver to a userspace driver using UIO.
However, there's one aspect of the system and driver that doesn't seem to be covered by UIO. The external board has a MMU and a DMA interface that allows it to copy data between the host system's RAM and its own internal memory.
The current kernel driver code looks up the physical address of a page of user-allocated memory by traversing the page table, and then writing the physical address to the external MMU. If we were to move the driver to userspace, this procedure would require exposing the physical address to user space, which insecure and thus a no-go.
What possibilities are there for programming the MMU from a userspace driver?
For reference, here is the existing kernel driver code -- start from apex_driver.c. https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/981313
Simon
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