tree cbcb3f3e5677f24ad29c3ba3aea862f1432addee
parent bd1066894861939eb53b90fac16b61261d1b4e1e
author Barret Rhoden <brho@cs.berkeley.edu> 1581702902 -0500
committer Barret Rhoden <brho@cs.berkeley.edu> 1583266410 -0500

dma: add user DMA arenas

These are arenas of user virtual addresses.  The kernel can allocate
them.  When we run a kernel driver for a device in the user's address
space, these arenas will be used for DMA addresses.  i.e. addresses the
device can access.

I might be able to use these for UCQs or something in the future.  In
essence, they are kernel-allocated and kernel-freed userspace memory.

Arguably, we could try to use arenas to do the user VA allocation, and
then hook in to the specific item (e.g. anon memory, file cache,
preexisting page) in a second step.  In that sense, do_mmap() would call
the UVA arena allocator.

For now, just have the arena be a wrapper interface around do_mmap() is
fine. (arena->do_mmap, versus do_mmap->arena + other magic).

Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>