Advertise FEAT_MEC in AA64MMFR3 ID register for the Arm64 cpu max as a
first step to fully support FEAT_MEC.

The FEAT_MEC is an extension to FEAT_RME that implements multiple
Memory Encryption Contexts (MEC) so the memory in a realm can be
encrypted and accessing it from the wrong encryption context is not
possible. An encryption context allow the selection of a memory
encryption engine.

At this point, no real memory encryption is supported, but most software
stacks that rely on FEAT_MEC to run should work properly.

Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
---
 docs/system/arm/emulation.rst | 3 +++
 target/arm/tcg/cpu64.c        | 1 +
 2 files changed, 4 insertions(+)

diff --git a/docs/system/arm/emulation.rst b/docs/system/arm/emulation.rst
index 1c597d8673..d207a9f266 100644
--- a/docs/system/arm/emulation.rst
+++ b/docs/system/arm/emulation.rst
@@ -89,6 +89,9 @@ the following architecture extensions:
 - FEAT_LSE (Large System Extensions)
 - FEAT_LSE2 (Large System Extensions v2)
 - FEAT_LVA (Large Virtual Address space)
+- FEAT_MEC (Memory Encryption Contexts)
+
+  * This is a register-only implementation without encryption.
 - FEAT_MixedEnd (Mixed-endian support)
 - FEAT_MixedEndEL0 (Mixed-endian support at EL0)
 - FEAT_MOPS (Standardization of memory operations)
diff --git a/target/arm/tcg/cpu64.c b/target/arm/tcg/cpu64.c
index 173528175a..2c63940878 100644
--- a/target/arm/tcg/cpu64.c
+++ b/target/arm/tcg/cpu64.c
@@ -1249,6 +1249,7 @@ void aarch64_max_tcg_initfn(Object *obj)
 
     FIELD_DP64_IDREG(isar, ID_AA64MMFR3, TCRX, 1);       /* FEAT_TCR2 */
     FIELD_DP64_IDREG(isar, ID_AA64MMFR3, SCTLRX, 1);     /* FEAT_SCTLR2 */
+    FIELD_DP64_IDREG(isar, ID_AA64MMFR3, MEC, 1);        /* FEAT_MEC */
     FIELD_DP64_IDREG(isar, ID_AA64MMFR3, SPEC_FPACC, 1); /* FEAT_FPACC_SPEC */
 
     t = GET_IDREG(isar, ID_AA64ZFR0);
-- 
2.34.1

On 7/9/25 12:03, Gustavo Romero wrote:
> At this point, no real memory encryption is supported, but most software
> stacks that rely on FEAT_MEC to run should work properly.

s/most //?

Anyway,
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~

Hi Richard!

On 7/9/25 17:54, Richard Henderson wrote:
> On 7/9/25 12:03, Gustavo Romero wrote:
>> At this point, no real memory encryption is supported, but most software
>> stacks that rely on FEAT_MEC to run should work properly.
> 
> s/most //?
> 
> Anyway,
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

Thanks a lot for the reviews :)

I'm sending v5 addressing your comments.


Cheers
Gustavo