As a part of a research project, I'm trying to build publish/subscribe
shared memory semantics where the idea is to first map an vm_object as
read/write to a publisher's memory space, and then a COW shadow of
that later to the subscriber processes' memory space.
I've got to the point where the code works most of the time, but at
certain scenarios (which are hard to classify and seem slightly
random) the mapping goes wrong, and either the subscriber process has
no physical mapping at the supposed address or there appears some
random page. To me it appears as if the vm_object, vm_map etc data
structures are OK, but somehow the pmaps don't get right. I'm
currently using 7.1 RELEASE on amd64, but I'm planning to try the same
on -CURRENT as soon as I get it properly ported. I even tried calling
pmap_enter_object explicitly before returning to the user space, but
it doesn't seem to help.
Another thing is that there may be some bugs related OBJ_ONEMAPPING.
We need to explicitly clear it at places, and sometimes artificially
bump up the vm_object reference count to avoid code related to
ONEMAPPING from trashing the object's mappings. Is this a known issue?
Any advice?
--Pekka Nikander
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