kernel/arm/paging: zero out the bottom portion of the new pgdir

Change-Id: I899f288f451dd4c413403cd0e14a855f68355050
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4866
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Fredrik Holmqvist <fredrik.holmqvist@gmail.com>
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

ARM: sync up VM code with x86

No big functional reason for this, but rather keep it in sync now
then have to do lots of work later on, when there are major changes.
Once I have it fully fleshed out for ARM, I might take a look if
we can generalise it a little more, as there's lots of code
_exactly_ the same for both platforms (and other platforms in
progress using the same code).

* ARM: Major VM work
- This is mostly a copy of the x86 32bit paging method and infrastructure, this was copied for two reasons:
1) It is the most complete VM arch
2) The first ARM PAE patches have landed on alkml, so we will have to deal with it in the future as well,
and this infrastructure has proven to be ready ;)
- No protection features, or dirty/accessed tracking yet
- Lots of #if 0

but....

It boots all the way up to init_modules() now, and then dies because of a lack of (ARM) ELF relocation implementation!

Since at this point the VM can be fully initialised, I'm going to focus on CPU exceptions next, so we can get KDL to trigger
when it happens, and I can actually debug from there ;)


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@39206 a95241bf-73f2-0310-859d-f6bbb57e9c96

ARM: sync up VM code with x86

No big functional reason for this, but rather keep it in sync now
then have to do lots of work later on, when there are major changes.
Once I have it fully fleshed out for ARM, I might take a look if
we can generalise it a little more, as there's lots of code
_exactly_ the same for both platforms (and other platforms in
progress using the same code).

* ARM: Major VM work
- This is mostly a copy of the x86 32bit paging method and infrastructure, this was copied for two reasons:
1) It is the most complete VM arch
2) The first ARM PAE patches have landed on alkml, so we will have to deal with it in the future as well,
and this infrastructure has proven to be ready ;)
- No protection features, or dirty/accessed tracking yet
- Lots of #if 0

but....

It boots all the way up to init_modules() now, and then dies because of a lack of (ARM) ELF relocation implementation!

Since at this point the VM can be fully initialised, I'm going to focus on CPU exceptions next, so we can get KDL to trigger
when it happens, and I can actually debug from there ;)


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@39206 a95241bf-73f2-0310-859d-f6bbb57e9c96