Because there is no write-only hardware page protection on ia32,
a write-only page fault is handled just like a read/write one.
But the mi vm layer distinguishes between the write-only and the
read/write protections, so if the fault takes place in a write-only
region, the vm layer would think that the write-only operation is
trying to read from a write-only address and violates the page protection.
As a consequence, if you want to use the sound device in mmapped mode,
you'll have to map the playback buffer read/write instead of write-only.

I'd like to reverse the way read/write and write-only page faults
are handled, i.e., handle both of them like a write-only fault. Does
anyone know any reason why I shouldn't do that?  I'm currently running
a kernel with this modification and I have seen no ill-effect so far.


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