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.
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