= Proposed System Wide Change: AARCH64 - 48-bit VA =

Change owner(s):
* Jeremy Linton < jeremy DOT linton AT arm DOT com >

Enable 48bit VA on AARCH64

== Detailed Description ==
The current aarch64 kernel is using a 42-bit process virtual address
(VA) space and due to the way aarch64 paging works this limits the max
physical address as well. This is fairly limiting for some
applications, but aarch64 processors also have support for 48-bit
VA's. This is actually 1-bit more than the "47-bit" VA's currently
used on x86_64. This change is a fairly minor kernel configuration but
it has caused problems with mozjs and luajit based projects because
they have stored tags in their pointers in the 48th address bit. The
upstream mozjs project has been fixed, and there are a set of changes
outstanding for luajit. Futher there, have been patches applied to
rawhide to support it (bug #1242326, bug #1375305. bug #1375547), but
the packages dependent on js185 require a rebuild due to an ABI

== Scope ==
* Proposal owners:
The kernel config needs to be changed, and the core mozjs/luajit
tagging problems need to be resolved. This can either take the form of
patching the remaining mozjs packages that have not yet been patched
and rebuilding the affected js185 packages, or it can take the form of
moving dependent packages onto mozjs versions that have been patched.
Futher lua needs to either be updated to the latest mainline or the
critical patches need to be applied to the lua versions currently in

* Release engineering:
Release engineering needs to assure the js185 packages are rebuilt.
Peter Robinson has volunteered to assist in this.

* Policies and guidelines: N/A

* Trademark approval: N/A (not needed for this Change)
Jan Kuřík
Platform & Fedora Program Manager
Red Hat Czech s.r.o., Purkynova 99/71, 612 45 Brno, Czech Republic
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