Oliver Upton oliver.upton@linux.dev writes:
AmpereOne has an erratum in its implementation of FEAT_HAFDBS that required disabling the feature on the design. This was done by reporting the feature as not implemented in the ID register, although the corresponding control bits were not actually RES0. This does not align well with the requirements of the architecture, which mandates these bits be RES0 if HAFDBS isn't implemented.
The kernel's use of stage-1 is unaffected, as the HA and HD bits are only set if HAFDBS is detected in the ID register. KVM, on the other hand, relies on the RES0 behavior at stage-2 to use the same value for VTCR_EL2 on any cpu in the system. Mitigate the non-RES0 behavior by leaving VTCR_EL2.HA clear on affected systems.
Cc: stable@vger.kernel.org Cc: D Scott Phillips scott@os.amperecomputing.com Cc: Darren Hart darren@os.amperecomputing.com Signed-off-by: Oliver Upton oliver.upton@linux.dev
Acked-by: D Scott Phillips scott@os.amperecomputing.com