[Xen-devel] 32bit/PAE guest on 64bit hypervisor work

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

While originally I expected to get at least the fundamentals of this done
without need to change the ABI in any form, I quickly ran into issues with
the GDT layout (since the guest usable selectors are published I consider
them part of the ABI): Obviously, the selector values used to run a 32bit
guest should match those of the 32bit hv, and hence the GDT layout
needs to be changed for the 64bit hv. This is despite context switches
between 32bit and 64bit guests needing to switch the GDT, since
__HYPERVISOR_DS32 overlaps 32bit's FLAT_RING1_CS32. The GDT
switching itself will be necessary because the 32bit guest must not be
able to use FLAT_RING3_CS64.

Further, in order to prevent the patch(es) from growing unusably
large, will it be acceptable to submit incremental pieces of this work
without the whole thing working, yet?

Thanks, Jan

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