riscv/mmu.h

   1 // See LICENSE for license details.
   2
   3 #ifndef _RISCV_MMU_H
   4 #define _RISCV_MMU_H
   5
   6 #include "decode.h"
   7 #include "trap.h"
   8 #include "common.h"
   9 #include "config.h"
  10 #include "processor.h"
  11 #include "memtracer.h"
  12 #include <stdlib.h>
  13 #include <vector>
  14
  15 // virtual memory configuration
  16 #define PGSHIFT 12
  17 const reg_t PGSIZE = 1 << PGSHIFT;
  18
  19 struct insn_fetch_t
  20 {
  21   insn_func_t func;
  22   insn_t insn;
  23 };
  24
  25 struct icache_entry_t {
  26   reg_t tag;
  27   reg_t pad;
  28   insn_fetch_t data;
  29 };
  30
  31 // this class implements a processor's port into the virtual memory system.
  32 // an MMU and instruction cache are maintained for simulator performance.
  33 class mmu_t
  34 {
  35 public:
  36   mmu_t(char* _mem, size_t _memsz);
  37   ~mmu_t();
  38
  39   // template for functions that load an aligned value from memory
  40   #define load_func(type) \
  41     type##_t load_##type(reg_t addr) __attribute__((always_inline)) { \
  42       void* paddr = translate(addr, sizeof(type##_t), false, false); \
  43       return *(type##_t*)paddr; \
  44     }
  45
  46   // load value from memory at aligned address; zero extend to register width
  47   load_func(uint8)
  48   load_func(uint16)
  49   load_func(uint32)
  50   load_func(uint64)
  51
  52   // load value from memory at aligned address; sign extend to register width
  53   load_func(int8)
  54   load_func(int16)
  55   load_func(int32)
  56   load_func(int64)
  57
  58   // template for functions that store an aligned value to memory
  59   #define store_func(type) \
  60     void store_##type(reg_t addr, type##_t val) { \
  61       void* paddr = translate(addr, sizeof(type##_t), true, false); \
  62       *(type##_t*)paddr = val; \
  63     }
  64
  65   // store value to memory at aligned address
  66   store_func(uint8)
  67   store_func(uint16)
  68   store_func(uint32)
  69   store_func(uint64)
  70
  71   static const reg_t ICACHE_ENTRIES = 1024;
  72
  73   inline size_t icache_index(reg_t addr)
  74   {
  75     // for instruction sizes != 4, this hash still works but is suboptimal
  76     return (addr / 4) % ICACHE_ENTRIES;
  77   }
  78
  79   // load instruction from memory at aligned address.
  80   icache_entry_t* access_icache(reg_t addr) __attribute__((always_inline))
  81   {
  82     reg_t idx = icache_index(addr);
  83     icache_entry_t* entry = &icache[idx];
  84     if (likely(entry->tag == addr))
  85       return entry;
  86
  87     char* iaddr = (char*)translate(addr, 1, false, true);
  88     insn_bits_t insn = *(uint16_t*)iaddr;
  89     int length = insn_length(insn);
  90
  91     if (likely(length == 4)) {
  92       if (likely(addr % PGSIZE < PGSIZE-2))
  93         insn |= (insn_bits_t)*(int16_t*)(iaddr + 2) << 16;
  94       else
  95         insn |= (insn_bits_t)*(int16_t*)translate(addr + 2, 1, false, true) << 16;
  96     } else if (length == 2) {
  97       insn = (int16_t)insn;
  98     } else if (length == 6) {
  99       insn |= (insn_bits_t)*(int16_t*)translate(addr + 4, 1, false, true) << 32;
 100       insn |= (insn_bits_t)*(uint16_t*)translate(addr + 2, 1, false, true) << 16;
 101     } else {
 102       static_assert(sizeof(insn_bits_t) == 8, "insn_bits_t must be uint64_t");
 103       insn |= (insn_bits_t)*(int16_t*)translate(addr + 6, 1, false, true) << 48;
 104       insn |= (insn_bits_t)*(uint16_t*)translate(addr + 4, 1, false, true) << 32;
 105       insn |= (insn_bits_t)*(uint16_t*)translate(addr + 2, 1, false, true) << 16;
 106     }
 107
 108     insn_fetch_t fetch = {proc->decode_insn(insn), insn};
 109     icache[idx].tag = addr;
 110     icache[idx].data = fetch;
 111
 112     reg_t paddr = iaddr - mem;
 113     if (!tracer.empty() && tracer.interested_in_range(paddr, paddr + 1, false, true))
 114     {
 115       icache[idx].tag = -1;
 116       tracer.trace(paddr, length, false, true);
 117     }
 118     return &icache[idx];
 119   }
 120
 121   inline insn_fetch_t load_insn(reg_t addr)
 122   {
 123     return access_icache(addr)->data;
 124   }
 125
 126   void set_processor(processor_t* p) { proc = p; flush_tlb(); }
 127
 128   void flush_tlb();
 129   void flush_icache();
 130
 131   void register_memtracer(memtracer_t*);
 132
 133 private:
 134   char* mem;
 135   size_t memsz;
 136   processor_t* proc;
 137   memtracer_list_t tracer;
 138
 139   // implement an instruction cache for simulator performance
 140   icache_entry_t icache[ICACHE_ENTRIES];
 141
 142   // implement a TLB for simulator performance
 143   static const reg_t TLB_ENTRIES = 256;
 144   char* tlb_data[TLB_ENTRIES];
 145   reg_t tlb_insn_tag[TLB_ENTRIES];
 146   reg_t tlb_load_tag[TLB_ENTRIES];
 147   reg_t tlb_store_tag[TLB_ENTRIES];
 148
 149   // finish translation on a TLB miss and upate the TLB
 150   void* refill_tlb(reg_t addr, reg_t bytes, bool store, bool fetch);
 151
 152   // perform a page table walk for a given VA; set referenced/dirty bits
 153   reg_t walk(reg_t addr, bool supervisor, bool store, bool fetch);
 154
 155   // translate a virtual address to a physical address
 156   void* translate(reg_t addr, reg_t bytes, bool store, bool fetch)
 157     __attribute__((always_inline))
 158   {
 159     reg_t idx = (addr >> PGSHIFT) % TLB_ENTRIES;
 160     reg_t expected_tag = addr >> PGSHIFT;
 161     reg_t* tags = fetch ? tlb_insn_tag : store ? tlb_store_tag :tlb_load_tag;
 162     reg_t tag = tags[idx];
 163     void* data = tlb_data[idx] + addr;
 164
 165     if (unlikely(addr & (bytes-1)))
 166       store ? throw trap_store_address_misaligned(addr) :
 167       fetch ? throw trap_instruction_address_misaligned(addr) :
 168       throw trap_load_address_misaligned(addr);
 169
 170     if (likely(tag == expected_tag))
 171       return data;
 172
 173     return refill_tlb(addr, bytes, store, fetch);
 174   }
 175
 176   friend class processor_t;
 177 };
 178
 179 #endif