On Mon, Aug 19, 2024 at 04:44:52PM +0100, Mark Brown wrote:

On Mon, Aug 19, 2024 at 12:46:13PM +0100, Catalin Marinas wrote:

quoted

On Thu, Aug 01, 2024 at 01:06:46PM +0100, Mark Brown wrote:

quoted

quoted

+	/*
+	 * Ensure that GCS changes are observable by/from other PEs in
+	 * case of migration.
+	 */
+	if (task_gcs_el0_enabled(current) || task_gcs_el0_enabled(next))
+		gcsb_dsync();

quoted

Could we do the sysreg writing under this 'if' block? If no app is using
GCS (which would be the case for a while), it looks like unnecessary
sysreg accesses.

Yes, that should be fine I think.

I forgot when writing the above that we always allow reads from
GCSPR_EL0 in order to avoid corner cases for unwinders in the case of
asynchronous disable.  I'd expect that to be cheap to access though.