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:

quoted

+  - If EL2 is present:

quoted

+    - GCSCR_EL2 must be initialised to 0.

quoted

+ - 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.