- Enable kernel stack guard page.

- Unmap the unused kernel stack page that we cannot use because it is
  not aligned on a (PAGE_SIZE * 2) boundary.

2 files changed, 23 insertions, 8 deletions

diff --git a/sys/mips/include/param.h b/sys/mips/include/param.h
index 8edd48ece16a..9d487022439b 100644
--- a/sys/mips/include/param.h
+++ b/sys/mips/include/param.h
@@ -128,14 +128,13 @@
 #define	MAXDUMPPGS	1		/* xxx: why is this only one? */
 
 /*
- * NOTE: In FreeBSD, Uarea's don't have a fixed address.
- *	 Therefore, any code imported from OpenBSD which depends on
- *	 UADDR, UVPN and KERNELSTACK requires porting.
- * XXX: 3 stack pages?  Not 4 which would be more efficient from a tlb
- * XXX: point of view.
+ * The kernel stack needs to be aligned on a (PAGE_SIZE * 2) boundary.
+ *
+ * Although we allocate 3 pages for the kernel stack we end up using
+ * only the 2 pages that are aligned on a (PAGE_SIZE * 2) boundary.
  */
 #define	KSTACK_PAGES		3	/* kernel stack*/
-#define	KSTACK_GUARD_PAGES	0	/* pages of kstack guard; 0 disables */
+#define	KSTACK_GUARD_PAGES	1	/* pages of kstack guard; 0 disables */
 
 #define	UPAGES			2
 
diff --git a/sys/mips/mips/vm_machdep.c b/sys/mips/mips/vm_machdep.c
index f76dc4d74f0a..3f8e6cc7f29a 100644
--- a/sys/mips/mips/vm_machdep.c
+++ b/sys/mips/mips/vm_machdep.c
@@ -214,6 +214,16 @@ cpu_thread_swapin(struct thread *td)
 {
 	pt_entry_t *pte;
 	int i;
+	vm_offset_t unused_kstack_page;
+
+	/*
+	 * Unmap the unused kstack page.
+	 */
+	unused_kstack_page = td->td_kstack;
+	if (td->td_md.md_realstack == td->td_kstack)
+		unused_kstack_page += (KSTACK_PAGES - 1) * PAGE_SIZE;
+
+	pmap_kremove(unused_kstack_page);
 
 	/*
 	 * The kstack may be at a different physical address now.
@@ -239,13 +249,19 @@ cpu_thread_swapout(struct thread *td)
 void
 cpu_thread_alloc(struct thread *td)
 {
+	vm_offset_t unused_kstack_page;
 	pt_entry_t *pte;
 	int i;
 
-	if(td->td_kstack & (1 << PAGE_SHIFT))
+	if (td->td_kstack & (1 << PAGE_SHIFT)) {
 		td->td_md.md_realstack = td->td_kstack + PAGE_SIZE;
-	else
+		unused_kstack_page = td->td_kstack;
+	} else {
 		td->td_md.md_realstack = td->td_kstack;
+		unused_kstack_page = td->td_kstack +
+					(KSTACK_PAGES - 1) * PAGE_SIZE;
+	}
+	pmap_kremove(unused_kstack_page);
 
 	td->td_pcb = (struct pcb *)(td->td_md.md_realstack +
 	    (td->td_kstack_pages - 1) * PAGE_SIZE) - 1;