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 <vector>
  13
  14 // virtual memory configuration
  15 typedef reg_t pte_t;
  16 const reg_t LEVELS = sizeof(pte_t) == sizeof(uint64_t) ? 3 : 2;
  17 const reg_t PGSHIFT = 13;
  18 const reg_t PGSIZE = 1 << PGSHIFT;
  19 const reg_t PTIDXBITS = PGSHIFT - (sizeof(pte_t) == 8 ? 3 : 2);
  20 const reg_t VPN_BITS = PTIDXBITS * LEVELS;
  21 const reg_t PPN_BITS = 8*sizeof(reg_t) - PGSHIFT;
  22 const reg_t VA_BITS = VPN_BITS + PGSHIFT;
  23
  24 // page table entry (PTE) fields
  25 #define PTE_T    0x001 // Entry is a page Table descriptor
  26 #define PTE_E    0x002 // Entry is a page table Entry
  27 #define PTE_R    0x004 // Referenced
  28 #define PTE_D    0x008 // Dirty
  29 #define PTE_UX   0x010 // User eXecute permission
  30 #define PTE_UW   0x020 // User Read permission
  31 #define PTE_UR   0x040 // User Write permission
  32 #define PTE_SX   0x080 // Supervisor eXecute permission
  33 #define PTE_SW   0x100 // Supervisor Read permission
  34 #define PTE_SR   0x200 // Supervisor Write permission
  35 #define PTE_PERM (PTE_SR | PTE_SW | PTE_SX | PTE_UR | PTE_UW | PTE_UX)
  36 #define PTE_PPN_SHIFT  13 // LSB of physical page number in the PTE
  37
  38 // this class implements a processor's port into the virtual memory system.
  39 // an MMU and instruction cache are maintained for simulator performance.
  40 class mmu_t
  41 {
  42 public:
  43   mmu_t(char* _mem, size_t _memsz);
  44   ~mmu_t();
  45
  46   // template for functions that load an aligned value from memory
  47   #define load_func(type) \
  48     type##_t load_##type(reg_t addr) { \
  49       if(unlikely(addr % sizeof(type##_t))) \
  50       { \
  51         badvaddr = addr; \
  52         throw trap_load_address_misaligned; \
  53       } \
  54       reg_t paddr = translate(addr, sizeof(type##_t), false, false); \
  55       return *(type##_t*)(mem + paddr); \
  56     }
  57
  58   // load value from memory at aligned address; zero extend to register width
  59   load_func(uint8)
  60   load_func(uint16)
  61   load_func(uint32)
  62   load_func(uint64)
  63
  64   // load value from memory at aligned address; sign extend to register width
  65   load_func(int8)
  66   load_func(int16)
  67   load_func(int32)
  68   load_func(int64)
  69
  70   // template for functions that store an aligned value to memory
  71   #define store_func(type) \
  72     void store_##type(reg_t addr, type##_t val) { \
  73       if(unlikely(addr % sizeof(type##_t))) \
  74       { \
  75         badvaddr = addr; \
  76         throw trap_store_address_misaligned; \
  77       } \
  78       reg_t paddr = translate(addr, sizeof(type##_t), true, false); \
  79       *(type##_t*)(mem + paddr) = val; \
  80     }
  81
  82   // store value to memory at aligned address
  83   store_func(uint8)
  84   store_func(uint16)
  85   store_func(uint32)
  86   store_func(uint64)
  87
  88   struct insn_fetch_t
  89   {
  90     insn_t insn;
  91     insn_func_t func;
  92   };
  93
  94   // load instruction from memory at aligned address.
  95   // (needed because instruction alignment requirement is variable
  96   // if RVC is supported)
  97   // returns the instruction at the specified address, given the current
  98   // RVC mode.  func is set to a pointer to a function that knows how to
  99   // execute the returned instruction.
 100   inline insn_fetch_t load_insn(reg_t addr, bool rvc)
 101   {
 102     #ifdef RISCV_ENABLE_RVC
 103     if(addr % 4 == 2 && rvc) // fetch across word boundary
 104     {
 105       reg_t addr_lo = translate(addr, 2, false, true);
 106       insn_fetch_t fetch;
 107       fetch.insn.bits = *(uint16_t*)(mem + addr_lo);
 108       fetch.func = get_insn_func(fetch.insn, sr);
 109
 110       if(!INSN_IS_RVC(fetch.insn.bits))
 111       {
 112         reg_t addr_hi = translate(addr+2, 2, false, true);
 113         fetch.insn.bits |= (uint32_t)*(uint16_t*)(mem + addr_hi) << 16;
 114       }
 115       return fetch;
 116     }
 117     else
 118     #endif
 119     {
 120       reg_t idx = (addr/sizeof(insn_t)) % ICACHE_ENTRIES;
 121       insn_fetch_t fetch;
 122       if (unlikely(icache_tag[idx] != addr))
 123       {
 124         reg_t paddr = translate(addr, sizeof(insn_t), false, true);
 125         fetch.insn = *(insn_t*)(mem + paddr);
 126         fetch.func = get_insn_func(fetch.insn, sr);
 127
 128         reg_t idx = (paddr/sizeof(insn_t)) % ICACHE_ENTRIES;
 129         icache_tag[idx] = addr;
 130         icache_data[idx] = fetch.insn;
 131         icache_func[idx] = fetch.func;
 132
 133         if (tracer.interested_in_range(paddr, paddr + sizeof(insn_t), false, true))
 134         {
 135           icache_tag[idx] = -1;
 136           tracer.trace(paddr, sizeof(insn_t), false, true);
 137         }
 138       }
 139       fetch.insn = icache_data[idx];;
 140       fetch.func = icache_func[idx];
 141       return fetch;
 142     }
 143   }
 144
 145   // get the virtual address that caused a fault
 146   reg_t get_badvaddr() { return badvaddr; }
 147
 148   // get/set the page table base register
 149   reg_t get_ptbr() { return ptbr; }
 150   void set_ptbr(reg_t addr) { ptbr = addr & ~(PGSIZE-1); flush_tlb(); }
 151   // keep the MMU in sync with processor mode
 152   void set_sr(uint32_t _sr) { sr = _sr; }
 153
 154   // flush the TLB and instruction cache
 155   void flush_tlb();
 156   void flush_icache();
 157
 158   void register_memtracer(memtracer_t*);
 159
 160 private:
 161   char* mem;
 162   size_t memsz;
 163   reg_t badvaddr;
 164   reg_t ptbr;
 165   uint32_t sr;
 166   memtracer_list_t tracer;
 167
 168   // implement a TLB for simulator performance
 169   static const reg_t TLB_ENTRIES = 256;
 170   reg_t tlb_data[TLB_ENTRIES];
 171   reg_t tlb_insn_tag[TLB_ENTRIES];
 172   reg_t tlb_load_tag[TLB_ENTRIES];
 173   reg_t tlb_store_tag[TLB_ENTRIES];
 174
 175   // implement an instruction cache for simulator performance
 176   static const reg_t ICACHE_ENTRIES = 256;
 177   insn_t icache_data[ICACHE_ENTRIES];
 178   insn_func_t icache_func[ICACHE_ENTRIES];
 179   reg_t icache_tag[ICACHE_ENTRIES];
 180
 181   // finish translation on a TLB miss and upate the TLB
 182   reg_t refill_tlb(reg_t addr, reg_t bytes, bool store, bool fetch);
 183
 184   // perform a page table walk for a given virtual address
 185   pte_t walk(reg_t addr);
 186
 187   // translate a virtual address to a physical address
 188   reg_t translate(reg_t addr, reg_t bytes, bool store, bool fetch)
 189   {
 190     reg_t idx = (addr >> PGSHIFT) % TLB_ENTRIES;
 191
 192     reg_t* tlb_tag = fetch ? tlb_insn_tag : store ? tlb_store_tag :tlb_load_tag;
 193     reg_t expected_tag = addr & ~(PGSIZE-1);
 194     if(likely(tlb_tag[idx] == expected_tag))
 195       return ((uintptr_t)addr & (PGSIZE-1)) + tlb_data[idx];
 196
 197     return refill_tlb(addr, bytes, store, fetch);
 198   }
 199
 200   friend class processor_t;
 201 };
 202
 203 #endif