We already do this on the 64bit side. We reuse the kernel and the
identity parts from the core kernel page tables but it is actually
a distinct page table.
x86_64 has not had the identity mappings mapped in any of the
normal page tables since the relocatable kernel support was merged
a while ago.
Only on the 32bit side does this still remain an issue. I don't know
if what we can do optimization wise there. Emulating the 64bit code
and having a dedicated top level pgd (as part of the trampoline)
and then a mapping into it the kernel identity mapping and the kernel
mapping (which are the same on 32bit) should work fairly easily.
It is just a handful of pgd entries, and then in the actual kernel
entry code we reload %cr3 with the appropriate kernel page table
and we should be fine. No need for an explicit zap there at all.
Eric
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