diff --git a/kernel/riscv.h b/kernel/riscv.h
index 9df3cc0..f46ba59 100644
--- a/kernel/riscv.h
+++ b/kernel/riscv.h
@@ -338,7 +338,7 @@ sfence_vma()
 
 #define PTE2PA(pte) (((pte) >> 10) << 12)
 
-#define PTE_FLAGS(pte) ((pte) & (PTE_V|PTE_R|PTE_W|PTE_X|PTE_U))
+#define PTE_FLAGS(pte) ((pte) & 0x3FF)
 
 // extract the three 9-bit page table indices from a virtual address.
 #define PXMASK          0x1FF // 9 bits
diff --git a/kernel/trap.c b/kernel/trap.c
index e96a542..ca732f2 100644
--- a/kernel/trap.c
+++ b/kernel/trap.c
@@ -95,10 +95,10 @@ usertrapret(void)
   // now from kerneltrap() to usertrap().
   intr_off();
 
-  // send interrupts and exceptions to trampoline.S
+  // send syscalls, interrupts, and exceptions to trampoline.S
   w_stvec(TRAMPOLINE + (uservec - trampoline));
 
-  // set up values that uservec will need when
+  // set up trapframe values that uservec will need when
   // the process next re-enters the kernel.
   p->tf->kernel_satp = r_satp();         // kernel page table
   p->tf->kernel_sp = p->kstack + PGSIZE; // process's kernel stack
diff --git a/kernel/vm.c b/kernel/vm.c
index 7524998..e0bc728 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -314,9 +314,9 @@ uvmcopy(pagetable_t old, pagetable_t new, uint64 sz)
 
   for(i = 0; i < sz; i += PGSIZE){
     if((pte = walk(old, i, 0)) == 0)
-      panic("copyuvm: pte should exist");
+      panic("uvmcopy: pte should exist");
     if((*pte & PTE_V) == 0)
-      panic("copyuvm: page not present");
+      panic("uvmcopy: page not present");
     pa = PTE2PA(*pte);
     flags = PTE_FLAGS(*pte);
     if((mem = kalloc()) == 0)