On Fri, Mar 19, 2021 at 07:51:58AM +0100, Christoph Hellwig wrote:

On Thu, Mar 18, 2021 at 12:46:53PM -0700, Keith Busch wrote:

quoted

I don't think it should require user space modifications. Just mmap the
current resource as-is but let the driver allow read-only in the
precense of CONFIG_IO_STRICT_DEVMEM. The below is a rough idea of what I
had in mind (compile tested only, and a proper solution should restrict
access to a specific address range)

I think this is a horrible idea.  Userspace has no business touching
registers even read-only.  MMIO reads can have side effects as well,
intentional or unintentional, and we also open up a whole can of worms
of mismatched memory attributes.

I was thinking the driver wouldn't opt-in if there were read side
effects, but yeah, it's too fragile. I withdraw the suggestion.

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