feat(cpufeat): add ENABLE_FEAT_LS64_ACCDATA
Armv8.6 introduced the FEAT_LS64 extension, which provides a 64 *byte*
store instruction. A related instruction is ST64BV0, which will replace
the lowest 32 bits of the data with a value taken from the ACCDATA_EL1
system register (so that EL0 cannot alter them).
Using that ST64BV0 instruction and accessing the ACCDATA_EL1 system
register is guarded by two SCR_EL3 bits, which we should set to avoid a
trap into EL3, when lower ELs use one of those.
Add the required bits and pieces to make this feature usable:
- Add the ENABLE_FEAT_LS64_ACCDATA build option (defaulting to 0).
- Add the CPUID and SCR_EL3 bit definitions associated with FEAT_LS64.
- Add a feature check to check for the existing four variants of the
LS64 feature and detect future extensions.
- Add code to save and restore the ACCDATA_EL1 register on
secure/non-secure context switches.
- Enable the feature with runtime detection for FVP and Arm FPGA.
Please note that the *basic* FEAT_LS64 feature does not feature any trap
bits, it's only the addition of the ACCDATA_EL1 system register that
adds these traps and the SCR_EL3 bits.
Change-Id: Ie3e2ca2d9c4fbbd45c0cc6089accbb825579138a
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index cd10cd6..ab0b94d 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -499,6 +499,11 @@
The flag is automatically disabled when the target
architecture is AArch32.
+- ``ENABLE_FEAT_LS64_ACCDATA``: Numeric value to enable access and save and
+ restore the ACCDATA_EL1 system register, at EL2 and below. This flag can
+ take the values 0 to 2, to align with the ``ENABLE_FEAT`` mechanism.
+ Default value is ``0``.
+
- ``ENABLE_MPMM``: Boolean option to enable support for the Maximum Power
Mitigation Mechanism supported by certain Arm cores, which allows the SoC
firmware to detect and limit high activity events to assist in SoC processor