W dniu 2.05.2024 o 12:37, Peter Maydell pisze:
* what are the constraints on the Aff* fields (eg that kernel commit suggests Aff0 shouldn't be > 15)?
This one is apparently related to GICv3 -- if the GIC doesn't implement RangeSelector support in ICC_SGI0R_EL1 and other places (advertised via GICD_TYPER.RSS and ICC_CTLR_EL1.SS) then there's no way to send an SGI to a CPU whose Aff0 is outside [0..15], and so you shouldn't build a system with Aff0 > 15. QEMU's GICv3 doesn't implement the RSS functionality (though it wouldn't be hard to add if we really cared), so we should also keep Aff0 in [0..15].
Arm/virt uses 8 cores/cluster on GICv2 and 16 cores/cluster on GICv3 as this is amount of SGI target-list bits available.
Arm/sbsa-ref goes with 8 cores per cluster by use of ARM_DEFAULT_CPUS_PER_CLUSTER.
We have ARM_DEFAULT_CPUS_PER_CLUSTER = 8, which does keep us in that range. I don't think there's really a good reason for it to be 8 rather than 16: this might be legacy from GICv2?
GICv2 supported only 8 cores.
