fix(cm): change back owning security state when a feature is disabled
Patch fc7dca72ba656e5f147487b20f9f0fb6eb39e116 changed the owning
security states of the TRBE and SPE buffers to NS. The thinking was that
this would assist SMCCC feature availability to more easily determine
if the feature is enabled or disabled. However, that only changed bit 0
while the SMCCC feature only looks at bit 1 so this change is redundant.
It was also meant to tighten security but that was done by
73d98e37593f4a4044dd28f52127cdc890911c0c instead.
Annoyingly, FEAT_TRBE has TRBIDR_EL1 which reports that programming is
allowed when the current security state owns the buffer even when the
MDCR_EL3 setting disallows this in practice.
So revert the functional aspect of the patch as it causes linux panics
with ERRATA_A520_2938996. Keep the defines as they are used elsewhere.
Change-Id: I39463d585df89aee44d1996137616da85d678f41
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
diff --git a/lib/extensions/trbe/trbe.c b/lib/extensions/trbe/trbe.c
index d8eb4c2..24d88ae 100644
--- a/lib/extensions/trbe/trbe.c
+++ b/lib/extensions/trbe/trbe.c
@@ -35,13 +35,12 @@
u_register_t mdcr_el3_val = read_ctx_reg(state, CTX_MDCR_EL3);
/*
- * MDCR_EL3.{NSTBE,NSTB} = 0b0, 0b10
+ * MDCR_EL3.{NSTBE,NSTB} = 0b0, 0b00
* Disable access of trace buffer control registers from lower ELs in
- * any security state. Non-secure owns the buffer.
+ * any security state. Secure state owns the buffer.
*/
mdcr_el3_val &= ~(MDCR_NSTB(MDCR_NSTB_EL1));
mdcr_el3_val &= ~(MDCR_NSTBE_BIT);
- mdcr_el3_val |= MDCR_NSTB(MDCR_NSTB_EL3);
write_ctx_reg(state, CTX_MDCR_EL3, mdcr_el3_val);
}