pmp: do not suppress pmpcfg writes for OFF or empty-range TOR entries under MML - #2495
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… under MML
With mseccfg.MML=1 and mseccfg.RLB=0, is_mml_m_exec_cfg checked only the L
bit and the {R,W,X} permission bits, ignoring the A (address-matching) field.
This caused three classes of writes to be incorrectly suppressed:
1. A=OFF, L=1, X=1 -- OFF creates no PMP rule; the write must not be blocked.
2. A=NA4, G=1, L=1, X=1 -- NA4 is converted to OFF when G>0, same as above.
3. A=TOR, L=1, X=1, pmpaddr[i-1] >= pmpaddr[i] -- empty range, no rule exists.
The Smepmp specification (v20260120, section 3.1) restricts writes only when
the resulting entry would produce a valid M-mode-only or Shared-Region rule.
An entry with A=OFF or an empty TOR range matches no address in any mode and
therefore cannot grant M-mode execute access.
Fix:
- is_mml_m_exec_cfg: add pmp_cfg.mode != PMP_MODE_OFF to the guard, covering
cases 1 and 2. The previous code silenced the unused mode field with a
parity reduction; that dummy assignment is removed.
- pmp_cfg_wr_suppress: add a tor_range_nonempty signal, generated per-region
inside the existing genvar loop:
* For region 0 the implicit TOR base is 0, so the range is non-empty iff
pmpaddr[0] != 0.
* For region i > 0, the range is non-empty iff pmpaddr[i-1] < pmpaddr[i].
Suppression is gated on tor_range_nonempty, covering case 3.
Fixes lowRISC#2491
Signed-off-by: Dev Tyagi <devtyagi3909@gmail.com>
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Fixes #2491
Root cause
is_mml_m_exec_cfgchecked only theLbit and the{R,W,X}permission bits, ignoring the address-matching field (A).pmp_cfg.modewas explicitly silenced with a parity reduction (logic unused_cfg = ^{pmp_cfg.mode}), making the suppression blind to whether the entry actually creates a PMP rule.This caused three classes of writes to be incorrectly suppressed under
MML=1, RLB=0:A=OFF, L=1, X=1A=NA4, G=1, L=1, X=1A=TOR, L=1, X=1, pmpaddr[i-1] >= pmpaddr[i]The Smepmp specification (section 3.1, v20260120) restricts writes only when the resulting entry produces a valid M-mode-only or Shared-Region rule. An entry with
A=OFFor an empty TOR range matches no address in any privilege mode.Fix
is_mml_m_exec_cfg: addpmp_cfg.mode != PMP_MODE_OFFto the guard. Removes the dummyunused_cfgparity assignment. Covers cases 1 and 2.pmp_cfg_wr_suppress: addtor_range_nonemptyper-region inside the existing genvar loop:pmpaddr[0] != 0pmpaddr[i-1] < pmpaddr[i]Suppression is gated on
tor_range_nonempty, covering case 3.