1 files changed, 389 insertions, 0 deletions
diff --git a/kernel/vm.c b/kernel/vm.c
new file mode 100644
index 0000000..0ea6bca
--- /dev/null
+++ b/kernel/vm.c
@@ -0,0 +1,389 @@
+#include "param.h"
+#include "types.h"
+#include "memlayout.h"
+#include "elf.h"
+#include "riscv.h"
+#include "defs.h"
+#include "fs.h"
+
+/*
+ * the kernel's page table.
+ */
+pagetable_t kernel_pagetable;
+
+extern char etext[];  // kernel.ld sets this to end of kernel code.
+
+extern char trampout[]; // trampoline.S
+
+/*
+ * create a direct-map page table for the kernel and
+ * turn on paging. called early, in supervisor mode.
+ * the page allocator is already initialized.
+ */
+void
+kvminit()
+{
+  kernel_pagetable = (pagetable_t) kalloc();
+  memset(kernel_pagetable, 0, PGSIZE);
+
+  // uart registers
+  mappages(kernel_pagetable, UART0, PGSIZE,
+           UART0, PTE_R | PTE_W);
+
+  // CLINT
+  mappages(kernel_pagetable, CLINT, 0x10000,
+           CLINT, PTE_R | PTE_W);
+
+  // PLIC
+  mappages(kernel_pagetable, PLIC, 0x4000000,
+           PLIC, PTE_R | PTE_W);
+
+  // map kernel text executable and read-only.
+  mappages(kernel_pagetable, KERNBASE, (uint64)etext-KERNBASE,
+           KERNBASE, PTE_R | PTE_X);
+
+  // map kernel data and the physical RAM we'll make use of.
+  mappages(kernel_pagetable, (uint64)etext, PHYSTOP-(uint64)etext,
+           (uint64)etext, PTE_R | PTE_W);
+
+  // map the qemu -initrd fs.img ramdisk
+  mappages(kernel_pagetable, RAMDISK, FSSIZE * BSIZE,
+           RAMDISK, PTE_R | PTE_W);
+
+  // map the trampoline for trap entry/exit to
+  // the highest virtual address in the kernel.
+  mappages(kernel_pagetable, TRAMPOLINE, PGSIZE,
+           (uint64)trampout, PTE_R | PTE_X);
+}
+
+// Switch h/w page table register to the kernel's page table,
+// and enable paging.
+void
+kvminithart()
+{
+  w_satp(MAKE_SATP(kernel_pagetable));
+}
+
+// Return the address of the PTE in page table pagetable
+// that corresponds to virtual address va.  If alloc!=0,
+// create any required page table pages.
+//
+// The risc-v Sv39 scheme has three levels of page table
+// pages. A page table page contains 512 64-bit PTEs.
+// A 64-bit virtual address is split into five fields:
+//   39..63 -- must be zero.
+//   30..38 -- 9 bits of level-2 index.
+//   21..39 -- 9 bits of level-1 index.
+//   12..20 -- 9 bits of level-0 index.
+//    0..12 -- 12 bits of byte offset within the page.
+static pte_t *
+walk(pagetable_t pagetable, uint64 va, int alloc)
+{
+  if(va >= MAXVA)
+    panic("walk");
+
+  for(int level = 2; level > 0; level--) {
+    pte_t *pte = &pagetable[PX(level, va)];
+    if(*pte & PTE_V) {
+      pagetable = (pagetable_t)PTE2PA(*pte);
+    } else {
+      if(!alloc || (pagetable = (pde_t*)kalloc()) == 0)
+        return 0;
+      memset(pagetable, 0, PGSIZE);
+      *pte = PA2PTE(pagetable) | PTE_V;
+    }
+  }
+  return &pagetable[PX(0, va)];
+}
+
+// Look up a virtual address, return the physical address,
+// Can only be used to look up user pages.
+// or 0 if not mapped.
+uint64
+walkaddr(pagetable_t pagetable, uint64 va)
+{
+  pte_t *pte;
+  uint64 pa;
+
+  pte = walk(pagetable, va, 0);
+  if(pte == 0)
+    return 0;
+  if((*pte & PTE_V) == 0)
+    return 0;
+  if((*pte & PTE_U) == 0)
+    return 0;
+  pa = PTE2PA(*pte);
+  return pa;
+}
+
+
+// Create PTEs for virtual addresses starting at va that refer to
+// physical addresses starting at pa. va and size might not
+// be page-aligned.
+void
+mappages(pagetable_t pagetable, uint64 va, uint64 size, uint64 pa, int perm)
+{
+  uint64 a, last;
+  pte_t *pte;
+
+  a = PGROUNDDOWN(va);
+  last = PGROUNDDOWN(va + size - 1);
+  for(;;){
+    if((pte = walk(pagetable, a, 1)) == 0)
+      panic("mappages: walk");
+    if(*pte & PTE_V)
+      panic("remap");
+    *pte = PA2PTE(pa) | perm | PTE_V;
+    if(a == last)
+      break;
+    a += PGSIZE;
+    pa += PGSIZE;
+  }
+}
+
+// Remove mappings from a page table. The mappings in
+// the given range must exist. Optionally free the
+// physical memory.
+void
+unmappages(pagetable_t pagetable, uint64 va, uint64 size, int do_free)
+{
+  uint64 a, last;
+  pte_t *pte;
+  uint64 pa;
+
+  a = PGROUNDDOWN(va);
+  last = PGROUNDDOWN(va + size - 1);
+  for(;;){
+    if((pte = walk(pagetable, a, 0)) == 0)
+      panic("unmappages: walk");
+    if((*pte & PTE_V) == 0){
+      printf("va=%p pte=%p\n", a, *pte);
+      panic("unmappages: not mapped");
+    }
+    if(PTE_FLAGS(*pte) == PTE_V)
+      panic("unmappages: not a leaf");
+    if(do_free){
+      pa = PTE2PA(*pte);
+      kfree((void*)pa);
+    }
+    *pte = 0;
+    if(a == last)
+      break;
+    a += PGSIZE;
+    pa += PGSIZE;
+  }
+}
+
+// create an empty user page table.
+pagetable_t
+uvmcreate()
+{
+  pagetable_t pagetable;
+  pagetable = (pagetable_t) kalloc();
+  if(pagetable == 0)
+    panic("uvmcreate: out of memory");
+  memset(pagetable, 0, PGSIZE);
+  return pagetable;
+}
+
+// Load the user initcode into address 0 of pagetable,
+// for the very first process.
+// sz must be less than a page.
+void
+uvminit(pagetable_t pagetable, uchar *src, uint sz)
+{
+  char *mem;
+
+  if(sz >= PGSIZE)
+    panic("inituvm: more than a page");
+  mem = kalloc();
+  memset(mem, 0, PGSIZE);
+  mappages(pagetable, 0, PGSIZE, (uint64)mem, PTE_W|PTE_R|PTE_X|PTE_U);
+  memmove(mem, src, sz);
+}
+
+// Allocate PTEs and physical memory to grow process from oldsz to
+// newsz, which need not be page aligned.  Returns new size or 0 on error.
+uint64
+uvmalloc(pagetable_t pagetable, uint64 oldsz, uint64 newsz)
+{
+  char *mem;
+  uint64 a;
+
+  if(newsz < oldsz)
+    return oldsz;
+
+  oldsz = PGROUNDUP(oldsz);
+  a = oldsz;
+  for(; a < newsz; a += PGSIZE){
+    mem = kalloc();
+    if(mem == 0){
+      uvmdealloc(pagetable, a, oldsz);
+      return 0;
+    }
+    memset(mem, 0, PGSIZE);
+    mappages(pagetable, a, PGSIZE, (uint64)mem, PTE_W|PTE_X|PTE_R|PTE_U);
+  }
+  return newsz;
+}
+
+// Deallocate user pages to bring the process size from oldsz to
+// newsz.  oldsz and newsz need not be page-aligned, nor does newsz
+// need to be less than oldsz.  oldsz can be larger than the actual
+// process size.  Returns the new process size.
+uint64
+uvmdealloc(pagetable_t pagetable, uint64 oldsz, uint64 newsz)
+{
+  if(newsz >= oldsz)
+    return oldsz;
+  unmappages(pagetable, newsz, oldsz - newsz, 1);
+  return newsz;
+}
+
+// Recursively free page table pages.
+// All leaf mappings must already have been removed.
+static void
+freewalk(pagetable_t pagetable)
+{
+  // there are 2^9 = 512 PTEs in a page table.
+  for(int i = 0; i < 512; i++){
+    pte_t pte = pagetable[i];
+    if((pte & PTE_V) && (pte & (PTE_R|PTE_W|PTE_X)) == 0){
+      // this PTE points to a lower-level page table.
+      uint64 child = PTE2PA(pte);
+      freewalk((pagetable_t)child);
+      pagetable[i] = 0;
+    } else if(pte & PTE_V){
+      panic("freewalk: leaf");
+    }
+  }
+  kfree((void*)pagetable);
+}
+
+// Free user memory pages,
+// then free page table pages.
+void
+uvmfree(pagetable_t pagetable, uint64 sz)
+{
+  unmappages(pagetable, 0, sz, 1);
+  freewalk(pagetable);
+}
+
+// Given a parent process's page table, copy
+// its memory into a child's page table.
+// Copies both the page table and the
+// physical memory.
+void
+uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
+{
+  pte_t *pte;
+  uint64 pa, i;
+  uint flags;
+  char *mem;
+
+  for(i = 0; i < sz; i += PGSIZE){
+    if((pte = walk(old, i, 0)) == 0)
+      panic("copyuvm: pte should exist");
+    if((*pte & PTE_V) == 0)
+      panic("copyuvm: page not present");
+    pa = PTE2PA(*pte);
+    flags = PTE_FLAGS(*pte);
+    if((mem = kalloc()) == 0)
+      panic("uvmcopy: kalloc failed");
+    memmove(mem, (char*)pa, PGSIZE);
+    mappages(new, i, PGSIZE, (uint64)mem, flags);
+  }
+}
+
+// Copy from kernel to user.
+// Copy len bytes from src to virtual address dstva in a given page table.
+// Return 0 on success, -1 on error.
+int
+copyout(pagetable_t pagetable, uint64 dstva, char *src, uint64 len)
+{
+  uint64 n, va0, pa0;
+
+  while(len > 0){
+    va0 = (uint)PGROUNDDOWN(dstva);
+    pa0 = walkaddr(pagetable, va0);
+    if(pa0 == 0)
+      return -1;
+    n = PGSIZE - (dstva - va0);
+    if(n > len)
+      n = len;
+    memmove((void *)(pa0 + (dstva - va0)), src, n);
+
+    len -= n;
+    src += n;
+    dstva = va0 + PGSIZE;
+  }
+  return 0;
+}
+
+// Copy from user to kernel.
+// Copy len bytes to dst from virtual address srcva in a given page table.
+// Return 0 on success, -1 on error.
+int
+copyin(pagetable_t pagetable, char *dst, uint64 srcva, uint64 len)
+{
+  uint64 n, va0, pa0;
+
+  while(len > 0){
+    va0 = (uint)PGROUNDDOWN(srcva);
+    pa0 = walkaddr(pagetable, va0);
+    if(pa0 == 0)
+      return -1;
+    n = PGSIZE - (srcva - va0);
+    if(n > len)
+      n = len;
+    memmove(dst, (void *)(pa0 + (srcva - va0)), n);
+
+    len -= n;
+    dst += n;
+    srcva = va0 + PGSIZE;
+  }
+  return 0;
+}
+
+// Copy a null-terminated string from user to kernel.
+// Copy bytes to dst from virtual address srcva in a given page table,
+// until a '\0', or max.
+// Return 0 on success, -1 on error.
+int
+copyinstr(pagetable_t pagetable, char *dst, uint64 srcva, uint64 max)
+{
+  uint64 n, va0, pa0;
+  int got_null = 0;
+
+  while(got_null == 0 && max > 0){
+    va0 = (uint)PGROUNDDOWN(srcva);
+    pa0 = walkaddr(pagetable, va0);
+    if(pa0 == 0)
+      return -1;
+    n = PGSIZE - (srcva - va0);
+    if(n > max)
+      n = max;
+
+    char *p = (char *) (pa0 + (srcva - va0));
+    while(n > 0){
+      if(*p == '\0'){
+        *dst = '\0';
+        got_null = 1;
+        break;
+      } else {
+        *dst = *p;
+      }
+      --n;
+      --max;
+      p++;
+      dst++;
+    }
+
+    srcva = va0 + PGSIZE;
+  }
+  if(got_null){
+    return 0;
+  } else {
+    return -1;
+  }
+}