Re: [PATCH 10/13] hw/intc/arm_gicv3_its: Drop TableDesc and CmdQDesc valid fields

[Richard Henderson <richard.henderson@linaro.org>]

On 2/2/22 06:32, Peter Maydell wrote:
> 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>
> ---
>   include/hw/intc/arm_gicv3_its_common.h |  2 --
>   hw/intc/arm_gicv3_its.c                | 31 ++++++++++++--------------
>   2 files changed, 14 insertions(+), 19 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~