[Xen-devel] compat mode argument translation area

["Jan Beulich" <JBeulich@xxxxxxxx>]

Hi Keir,

this, originally having been at a fixed location outside of Xen virtual
address ranges, has seen a number of changes over the years, with
the net effect that right now we're requiring an order-1 allocation
from the Xen heap. Obviously it would be much better if this got
populated with order-0 allocations from the domain heap.

Considering that there's going to be one such area per vCPU (less
those vCPU-s that don't need translation, i.e. 64-bit PV ones), it
seems undesirable to me to use vmap() for this purpose.

Instead I wonder whether we shouldn't go back to putting this at
a fixed address (5Gb or 8Gb) at least for PV guests, thus reducing
the virtual address range pressure (compared to the vmap()
approach as well as for the case that these areas might need
extending). Was there any other reason that you moved them out
of such a fixed area than wanting to use mostly the same code
for PV and HVM (which ought to be possible now that there's a
base pointer stored for each vCPU)?

An alternative might be to use another per-domain L3 slot for this.

Jan


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