fix pt invalidation bug + slight speedup

5c3e499d · Nickolai Zeldovich · 6477987b · 5c3e499d
--- a/kernel/vm.cc
+++ b/kernel/vm.cc
@@ -277,6 +277,7 @@ vmap::insert(vmnode *n, uptr vma_start, int dotlb)
  ANON_REGION("vmap::insert", &perfgroup);
  vma *e;
+  bool replaced = false;
  {
    // new scope to release the search lock before tlbflush
@@ -288,7 +289,7 @@ vmap::insert(vmnode *n, uptr vma_start, int dotlb)
      return -1;
    }
-    // XXX handle overlaps
+    // XXX handle overlaps, set replaced=true
    e = new vma(this, vma_start, vma_start+len, PRIVATE, n);
    if (e == 0) {
@@ -300,15 +301,18 @@ vmap::insert(vmnode *n, uptr vma_start, int dotlb)
  }
  bool needtlb = false;
+  if (replaced)
    updatepages(pml4, e->vma_start, e->vma_end, [&needtlb](atomic<pme_t> *p) {
        for (;;) {
          pme_t v = p->load();
          if (v & PTE_LOCK)
            continue;
-        if (cmpxch(p, v, (pme_t) 0))
+          if (!(v & PTE_P))
            break;
-        if (v != 0)
+          if (cmpxch(p, v, (pme_t) 0)) {
            needtlb = true;
+            break;
+          }
        }
      });
  if (needtlb && dotlb)
@@ -343,10 +347,12 @@ vmap::remove(uptr vma_start, uptr len)
        pme_t v = p->load();
        if (v & PTE_LOCK)
          continue;
-        if (cmpxch(p, v, (pme_t) 0))
+        if (!(v & PTE_P))
          break;
-        if (v != 0)
+        if (cmpxch(p, v, (pme_t) 0)) {
          needtlb = true;
+          break;
+        }
      }
    });
  if (needtlb)