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5 State Enable Access Control

When Smstateen is implemented, the mstateen0.CTR bit controls access to CTR register state from privilege modes less privileged than M-mode. When mstateen0.CTR=1, accesses to CTR register state behave as described in Section 2 and Section 3 above, while SCTRCLR behaves as described in Section 4.1. When mstateen0.CTR=0 and the privilege mode is less privileged than M-mode, the following operations raise an illegal-instruction exception:

  • Attempts to access sctrctl, vsctrctl, sctrdepth, or sctrstatus
  • Attempts to access sireg* when siselect is in 0x200..0x2FF, or vsireg* when vsiselect is in 0x200..0x2FF
  • Execution of the SCTRCLR instruction

When mstateen0.CTR=0, qualified control transfers executed in privilege modes less privileged than M-mode will continue to implicitly update entry registers and sctrstatus.

If the H extension is implemented and mstateen0.CTR=1, the hstateen0.CTR bit controls access to supervisor CTR state when V=1. This state includes sctrctl (really vsctrctl), sctrstatus, and sireg* (really vsireg*) when siselect (really vsiselect) is in 0x200..0x2FF. hstateen0.CTR is read-only 0 when mstateen0.CTR=0.

When mstateen0.CTR=1 and hstateen0.CTR=1, VS-mode accesses to supervisor CTR state behave as described in Section 2 and Section 3 above, while SCTRCLR behaves as described in Section 4.1. When mstateen0.CTR=1 and hstateen0.CTR=0, both VS-mode accesses to supervisor CTR state and VS-mode execution of SCTRCLR raise a virtual-instruction exception.

note

_sctrdepth_ is not included in the above list of supervisor CTR state controlled by hstateen0.CTR since accesses to sctrdepth from VS-mode raise a virtual-instruction exception regardless of the value of hstateen0.CTR.

When hstateen0.CTR=0, qualified control transfers executed while V=1 will continue to implicitly update entry registers and sctrstatus.

The CTR bit is bit 54 in mstateen0 and hstateen0.

note

See the Sscsrind spec for how bit 60 in mstateen0 and hstateen0 can also restrict access to sireg*/siselect and vsireg*/vsiselect from privilege modes less privileged than M-mode.