Currently we track in the TableDesc and CmdQDesc structs the state of
the GITS_BASER<n> and GITS_CBASER Valid bits.  However we aren't very
consistent abut checking the valid field: we test it in update_cte()
and update_dte(), but not anywhere else we look things up in tables.

The GIC specification says that it is UNPREDICTABLE if a guest fails
to set any of these Valid bits before enabling the ITS via
GITS_CTLR.Enabled.  So we can choose to handle Valid == 0 as
equivalent to a zero-length table.  This is in fact how we're already
catching this case in most of the table-access paths: when Valid is 0
we leave the num_entries fields in TableDesc or CmdQDesc set to zero,
and then the out-of-bounds check "index >= num_entries" that we have
to do anyway before doing any of these table lookups will always be
true, catching the no-valid-table case without any extra code.

So we can remove the checks on the valid field from update_cte()
and update_dte(): since these happen after the bounds check there
was never any case when the test could fail. That means the valid
fields would be entirely unused, so just remove them.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220201193207.2771604-11-peter.maydell@linaro.org