hw/intc/arm_gicv3: Insist that redist region capacity matches CPU count

Boards using the GICv3 need to configure it with both the total
number of CPUs and also the sizes of all the memory regions which
contain redistributors (one redistributor per CPU).  At the moment
the GICv3 checks that the number of CPUs specified is not too many to
fit in the defined redistributor regions, but in fact the code
assumes that the two match exactly.  For instance when we set the
GICR_TYPER.Last bit on the final redistributor in each region, we
assume that we don't need to consider the possibility of a region
being only half full of redistributors or even completely empty.  We
also assume in gicv3_redist_read() and gicv3_redist_write() that we
can calculate the CPU index from the offset within the MemoryRegion
and that this will always be in range.

Fortunately all the board code sets the redistributor region sizes to
exactly match the CPU count, so this isn't a visible bug.  We could
in theory make the GIC code handle non-full redistributor regions, or
have it automatically reduce the provided region sizes to match the
CPU count, but the simplest thing is just to strengthen the error
check and insist that the CPU count and redistributor region size
settings match exactly, since all the board code does that anyway.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220408141550.1271295-4-peter.maydell@linaro.org

1 files changed, 2 insertions, 2 deletions

diff --git a/hw/intc/arm_gicv3_common.c b/hw/intc/arm_gicv3_common.c
index 90204be25b..c797c82786 100644
--- a/hw/intc/arm_gicv3_common.c
+++ b/hw/intc/arm_gicv3_common.c
@@ -354,9 +354,9 @@ static void arm_gicv3_common_realize(DeviceState *dev, Error **errp)
     for (i = 0; i < s->nb_redist_regions; i++) {
         rdist_capacity += s->redist_region_count[i];
     }
-    if (rdist_capacity < s->num_cpu) {
+    if (rdist_capacity != s->num_cpu) {
         error_setg(errp, "Capacity of the redist regions(%d) "
-                   "is less than number of vcpus(%d)",
+                   "does not match the number of vcpus(%d)",
                    rdist_capacity, s->num_cpu);
         return;
     }