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     type##_t load_reserved_##type(reg_t addr) { \
  58       load_reservation = addr; \
  59       return load_##type(addr); \
  60     }
  61
  62   // load value from memory at aligned address; zero extend to register width
  63   load_func(uint8)
  64   load_func(uint16)
  65   load_func(uint32)
  66   load_func(uint64)
  67
  68   // load value from memory at aligned address; sign extend to register width
  69   load_func(int8)
  70   load_func(int16)
  71   load_func(int32)
  72   load_func(int64)
  73
  74   // template for functions that store an aligned value to memory
  75   #define store_func(type) \
  76     void store_##type(reg_t addr, type##_t val) { \
  77       if(unlikely(addr % sizeof(type##_t))) \
  78       { \
  79         badvaddr = addr; \
  80         throw trap_store_address_misaligned; \
  81       } \
  82       reg_t paddr = translate(addr, sizeof(type##_t), true, false); \
  83       *(type##_t*)(mem + paddr) = val; \
  84     } \
  85     reg_t store_conditional_##type(reg_t addr, type##_t val) { \
  86       if (addr == load_reservation) { \
  87         store_##type(addr, val); \
  88         return 0; \
  89       } else return 1; \
  90     }
  91
  92   // store value to memory at aligned address
  93   store_func(uint8)
  94   store_func(uint16)
  95   store_func(uint32)
  96   store_func(uint64)
  97
  98   struct insn_fetch_t
  99   {
 100     insn_func_t func;
 101     insn_t insn;
 102   };
 103
 104   // load instruction from memory at aligned address.
 105   inline insn_fetch_t load_insn(reg_t addr)
 106   {
 107     reg_t idx = (addr/sizeof(insn_t::itype)) % ICACHE_ENTRIES;
 108     if (unlikely(icache_tag[idx] != addr))
 109     {
 110       reg_t paddr = translate(addr, sizeof(insn_t::itype), false, true);
 111       insn_fetch_t fetch;
 112       fetch.insn.itype = *(decltype(insn_t::itype)*)(mem + paddr);
 113       fetch.func = proc->decode_insn(fetch.insn);
 114
 115       reg_t idx = (paddr/sizeof(insn_t::itype)) % ICACHE_ENTRIES;
 116       icache_tag[idx] = addr;
 117       icache_data[idx] = fetch;
 118
 119       if (tracer.interested_in_range(paddr, paddr + sizeof(insn_t::itype), false, true))
 120       {
 121         icache_tag[idx] = -1;
 122         tracer.trace(paddr, sizeof(insn_t::itype), false, true);
 123       }
 124     }
 125     return icache_data[idx];
 126   }
 127
 128   reg_t get_badvaddr() { return badvaddr; }
 129   reg_t get_ptbr() { return ptbr; }
 130   void set_ptbr(reg_t addr) { ptbr = addr & ~(PGSIZE-1); flush_tlb(); }
 131   void set_processor(processor_t* p) { proc = p; flush_tlb(); }
 132
 133   void flush_tlb();
 134   void flush_icache();
 135   void yield_load_reservation() { load_reservation = -1; }
 136
 137   void register_memtracer(memtracer_t*);
 138
 139 private:
 140   char* mem;
 141   size_t memsz;
 142   reg_t load_reservation;
 143   reg_t badvaddr;
 144   reg_t ptbr;
 145   processor_t* proc;
 146   memtracer_list_t tracer;
 147
 148   // implement an instruction cache for simulator performance
 149   static const reg_t ICACHE_ENTRIES = 256;
 150   insn_fetch_t icache_data[ICACHE_ENTRIES];
 151
 152   // implement a TLB for simulator performance
 153   static const reg_t TLB_ENTRIES = 256;
 154   reg_t tlb_data[TLB_ENTRIES];
 155   reg_t tlb_insn_tag[TLB_ENTRIES];
 156   reg_t tlb_load_tag[TLB_ENTRIES];
 157   reg_t tlb_store_tag[TLB_ENTRIES];
 158   reg_t icache_tag[ICACHE_ENTRIES];
 159
 160   // finish translation on a TLB miss and upate the TLB
 161   reg_t refill_tlb(reg_t addr, reg_t bytes, bool store, bool fetch);
 162
 163   // perform a page table walk for a given virtual address
 164   pte_t walk(reg_t addr);
 165
 166   // translate a virtual address to a physical address
 167   reg_t translate(reg_t addr, reg_t bytes, bool store, bool fetch)
 168   {
 169     reg_t idx = (addr >> PGSHIFT) % TLB_ENTRIES;
 170
 171     reg_t* tlb_tag = fetch ? tlb_insn_tag : store ? tlb_store_tag :tlb_load_tag;
 172     reg_t expected_tag = addr & ~(PGSIZE-1);
 173     if(likely(tlb_tag[idx] == expected_tag))
 174       return ((uintptr_t)addr & (PGSIZE-1)) + tlb_data[idx];
 175
 176     return refill_tlb(addr, bytes, store, fetch);
 177   }
 178
 179   friend class processor_t;
 180 };
 181
 182 #endif