On Thu, Aug 15, 2024 at 06:00:15PM +0100, Catalin Marinas wrote:
On Thu, Aug 01, 2024 at 01:06:31PM +0100, Mark Brown wrote:
- If EL2 is present:
- GCSCR_EL2 must be initialised to 0.
- If the kernel is entered at EL1 and EL2 is present:
- GCSCR_EL1 must be initialised to 0.
- GCSCRE0_EL1 must be initialised to 0.
Currently booting.rst doesn't list *_EL1 registers to be initialised when the kernel is entered at EL1, that would usually be the responsibility of EL1. The exception is some bits in SCTLR_EL1 around not entering with the MMU and caches enabled. But here I think it makes sense to add these GCS registers since if some random bits are set, they can affect kernels (and user apps) that don't have GCS support.
Right, exactly - the trouble here is that if we enter EL1 with GCS enabled we aren't able to do function calls until we either disable GCS or configure the MMU and allocate a GCS. This means that all existing kernels which haven't heard of GCS require that GCS be disabled prior to starting, they'll just fault within a couple of instructions whenever they reach the EL for which GCS is enabled so it seems sensible to just require that this is set up. It is hard to envision a scenario in which it would be reasonable to start in a different configuration.
Now I think about it I should move those two to not depend on EL2 being present, that's just cut'n'paste.
Don't we need HCRX_EL2.GCSEn to be set when entered at EL1?
Yes, if we want GCS to do anything. I've added this.