Lab pgtbl

tags: 6.1810

Speed up system calls

diff --git a/kernel/proc.c b/kernel/proc.c
index 959b778..72068b2 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -132,6 +132,13 @@ found:
     return 0;
   }
 
+  // Allocate a usyscall page.
+  if ((p->usyscall = (struct usyscall *)kalloc()) == 0) {
+    freeproc(p);
+    release(&p->lock);
+    return 0;
+  }
+
   // An empty user page table.
   p->pagetable = proc_pagetable(p);
   if(p->pagetable == 0){
@@ -145,6 +152,7 @@ found:
   memset(&p->context, 0, sizeof(p->context));
   p->context.ra = (uint64)forkret;
   p->context.sp = p->kstack + PGSIZE;
+  p->usyscall->pid = p->pid;
 
   return p;
 }
@@ -155,6 +163,9 @@ found:
 static void
 freeproc(struct proc *p)
 {
+  if (p->usyscall)
+    kfree((void*)p->usyscall);
+  p->usyscall = 0;
   if(p->trapframe)
     kfree((void*)p->trapframe);
   p->trapframe = 0;
@@ -202,6 +213,15 @@ proc_pagetable(struct proc *p)
     return 0;
   }
 
+  // map the usyscall page just below the trapframe page
+  if (mappages(pagetable, USYSCALL, PGSIZE,
+              (uint64)(p->usyscall), PTE_R | PTE_U) < 0) {
+    uvmunmap(pagetable, TRAPFRAME, 1, 0);
+    uvmunmap(pagetable, TRAMPOLINE, 1, 0);
+    uvmfree(pagetable, 0);
+    return 0;
+  }
+
   return pagetable;
 }
 
@@ -210,6 +230,7 @@ proc_pagetable(struct proc *p)
 void
 proc_freepagetable(pagetable_t pagetable, uint64 sz)
 {
+  uvmunmap(pagetable, USYSCALL, 1, 0);
   uvmunmap(pagetable, TRAMPOLINE, 1, 0);
   uvmunmap(pagetable, TRAPFRAME, 1, 0);
   uvmfree(pagetable, sz);
diff --git a/kernel/proc.h b/kernel/proc.h
index d021857..ef84dd1 100644
--- a/kernel/proc.h
+++ b/kernel/proc.h
@@ -100,6 +100,7 @@ struct proc {
   uint64 sz;                   // Size of process memory (bytes)
   pagetable_t pagetable;       // User page table
   struct trapframe *trapframe; // data page for trampoline.S
+  struct usyscall *usyscall;   // data page for usyscall
   struct context context;      // swtch() here to run process
   struct file *ofile[NOFILE];  // Open files
   struct inode *cwd;           // Current directory

Print a page table

diff --git a/kernel/defs.h b/kernel/defs.h
index a3c962b..487f4f2 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -173,6 +173,7 @@ uint64          walkaddr(pagetable_t, uint64);
 int             copyout(pagetable_t, uint64, char *, uint64);
 int             copyin(pagetable_t, char *, uint64, uint64);
 int             copyinstr(pagetable_t, char *, uint64, uint64);
+void            vmprint(pagetable_t);
 
 // plic.c
 void            plicinit(void);
diff --git a/kernel/exec.c b/kernel/exec.c
index e18bbb6..89d5d7c 100644
--- a/kernel/exec.c
+++ b/kernel/exec.c
@@ -128,6 +128,8 @@ exec(char *path, char **argv)
   p->trapframe->sp = sp; // initial stack pointer
   proc_freepagetable(oldpagetable, oldsz);
 
+  if (p->pid == 1)
+    vmprint(p->pagetable);
   return argc; // this ends up in a0, the first argument to main(argc, argv)
 
  bad:
diff --git a/kernel/vm.c b/kernel/vm.c
index 9f69783..268236d 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -437,3 +437,37 @@ copyinstr(pagetable_t pagetable, char *dst, uint64 srcva, uint64 max)
     return -1;
   }
 }
+
+void
+printpte(pte_t pte, int index, int level)
+{
+  for (int i = level; i >= 0; i--)
+      printf(" ..");
+  printf("%d: pte %p pa %p\n", index, pte, PTE2PA(pte));
+}
+
+void
+_vmprint(pagetable_t pagetable, int level)
+{
+  for (int i = 0; i < 512; i++) {
+    pte_t pte = pagetable[i];
+    if(pte & PTE_V) { 
+      printpte(pte, i, level);
+      if ((pte & (PTE_R|PTE_W|PTE_X)) == 0) {
+      // this PTE points to a lower-level page table.
+        uint64 child = PTE2PA(pte);
+        _vmprint((pagetable_t)child, level + 1);
+      }
+    }
+  }
+}
+
+void 
+vmprint(pagetable_t pagetable)
+{
+  printf("page table 0x%16x\n", (uint64)pagetable);
+  _vmprint(pagetable, 0);
+}

Detect which pages have been accessed

diff --git a/kernel/riscv.h b/kernel/riscv.h
index 20a01db..efbb6f5 100644
--- a/kernel/riscv.h
+++ b/kernel/riscv.h
@@ -343,6 +343,7 @@ typedef uint64 *pagetable_t; // 512 PTEs
 #define PTE_W (1L << 2)
 #define PTE_X (1L << 3)
 #define PTE_U (1L << 4) // user can access
+#define PTE_A (1L << 6) // access bit
 
 // shift a physical address to the right place for a PTE.
 #define PA2PTE(pa) ((((uint64)pa) >> 12) << 10)
diff --git a/kernel/sysproc.c b/kernel/sysproc.c
index 88644b2..0948503 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -75,6 +75,34 @@ int
 sys_pgaccess(void)
 {
   // lab pgtbl: your code here.
+  uint64 va, addr;
+  int size;
+
+  argaddr(0, &va);
+  argint(1, &size);
+  argaddr(2, &addr);
+
+  struct proc *proc = myproc();
+  pagetable_t pagetable = proc->pagetable;
+  uint64 a, last;
+  pte_t *pte;
+  unsigned int abits = 0;
+
+  if(size == 0)
+    panic("pgaccess: size");
+  
+  a = PGROUNDDOWN(va);
+  last = PGROUNDDOWN(va + size * PGSIZE - 1);
+  last = last > MAXVA ? MAXVA : last;
+  for (unsigned i = 0; i < 32 && a <= last; i++, a += PGSIZE) {
+    if((pte = walk(pagetable, a, 0)) == 0)
+      continue;
+    if(*pte & PTE_A) {
+      abits |= (1 << i);
+      *pte &= ~PTE_A;
+    }
+  }
+
+  copyout(pagetable, addr, (char *)&abits, sizeof(abits));
   return 0;
 }
 #endif