get rid of mmio_ok checks

before this patch, hart access to debug module region was controlled in
two places:

1. pmp_ok performed the normal architectural PMP checks, but **bypassed** them
   for debug module region accesses while the hart was in debug mode.
2. mmio_ok **rejected** debug module region accesses from harts outside
   debug mode.  Processor-less debug_mmu accesses remained allowed.

This patch moves the control decision entirely to pmp_ok routine:
**allow** debug module regoin accesses in debug mode and **deny** them
otherwise.  This check is run before the no-PMP fast path, making
mmio_ok redundant.

Additionally, we flush the TLB on processor reset because it may
contain stale entries from the time while hart was in debug mode.

riscv/mmu.cc

@@ -158,20 +158,8 @@ static reg_t reg_from_bytes(size_t len, const uint8_t* bytes)
   return res;
 }
 
-bool mmu_t::mmio_ok(reg_t paddr, size_t len, access_type UNUSED type)
-{
-  // Disallow access to debug region when not in debug mode
-  if (proc && sim && sim->is_debug_module_access(paddr, len) && !proc->state.debug_mode)
-    return false;
-
-  return true;
-}
-
 bool mmu_t::mmio_fetch(reg_t paddr, size_t len, uint8_t* bytes)
 {
-  if (!mmio_ok(paddr, len, FETCH))
-    return false;
-
   return sim->mmio_fetch(paddr, len, bytes);
 }
 
@@ -191,9 +179,6 @@ bool mmu_t::mmio(reg_t paddr, size_t len, uint8_t* bytes, access_type type)
   bool naturally_aligned = (paddr & (len - 1)) == 0;
 
   if (power_of_2 && naturally_aligned) {
-    if (!mmio_ok(paddr, len, type))
-      return false;
-
     if (type == STORE)
       return sim->mmio_store(paddr, len, bytes);
     else
@@ -533,13 +518,13 @@ std::optional<base_pmpaddr_csr_t*> mmu_t::pmp_lookup(reg_t addr, reg_t len, size
 
 bool mmu_t::pmp_ok(reg_t addr, reg_t len, access_type type, reg_t mode, bool hlvx)
 {
-  if (!proc || proc->n_pmp == 0)
-    return true;
-
   // The debug module implementation relies on firmware (ROM) owned by spike.
-  // When executing code from this firmware we keep target PMP rules from
-  // blocking the simulator-owned debug firmware.
-  if (proc->state.debug_mode && sim && sim->is_debug_module_access(addr, len))
+  // The Debug Module address region is hidden from normal software.
+  // A hart can access it only in debug mode.
+  if (proc && sim && sim->is_debug_module_access(addr, len))
+    return proc->state.debug_mode;
+
+  if (!proc || proc->n_pmp == 0)
     return true;
 
   if (auto pmp = pmp_lookup(addr, len, 0, proc->n_pmp); pmp.has_value())

riscv/mmu.h

@@ -444,7 +444,6 @@ private:
   bool mmio_load(reg_t paddr, size_t len, uint8_t* bytes);
   bool mmio_store(reg_t paddr, size_t len, const uint8_t* bytes);
   bool mmio(reg_t paddr, size_t len, uint8_t* bytes, access_type type);
-  bool mmio_ok(reg_t paddr, size_t len, access_type type);
 
   void check_triggers(triggers::operation_t operation,
     reg_t addr, bool virt, std::size_t data_size, const std::uint8_t* bytes);

riscv/processor.cc

@@ -150,6 +150,7 @@ void processor_t::reset()
 {
   xlen = isa.get_max_xlen();
   state.reset(this, isa.get_max_isa());
+  mmu->flush_tlb();
   if (any_vector_extensions())
     VU.reset();
   in_wfi = false;