diff --git a/sys/alpha/alpha/exception.s b/sys/alpha/alpha/exception.s
index bc8ee5730df..b3bf1dceab4 100644
--- a/sys/alpha/alpha/exception.s
+++ b/sys/alpha/alpha/exception.s
@@ -140,16 +140,19 @@ XentSys1: LDGP(pv)
 	beq	t1, exception_return
 
 	/* set the hae register if this process has specified a value */
-	ldq	t0, GD_CURPROC(globalp)
-	beq	t0, 3f
-	ldq	t1, P_MD_FLAGS(t0)
+	ldq	s0, GD_CURPROC(globalp)
+	ldq	t1, P_MD_FLAGS(s0)
 	and	t1, MDP_HAEUSED
 	beq	t1, 3f
-	ldq	a0, P_MD_HAE(t0)
+	ldq	a0, P_MD_HAE(s0)
 	ldq	pv, chipset + CHIPSET_WRITE_HAE
 	CALL((pv))
 3:	
-	
+#ifdef SMP
+	/* leave the kernel */
+	stl	zero, P_MD_KERNNEST(s0)
+#endif
+
 	/* restore the registers, and return */
 	ldq	v0,(FRAME_V0*8)(sp)
 	ldq	s0,(FRAME_S0*8)(sp)
@@ -253,28 +256,42 @@ LEAF(exception_return, 1)			/* XXX should be NESTED */
 	br	pv, Ler1
 Ler1:	LDGP(pv)
 
-	ldq	s1, (FRAME_PS * 8)(sp)		/* get the saved PS */
-	and	s1, ALPHA_PSL_IPL_MASK, t0	/* look at the saved IPL */
-	bne	t0, Lrestoreregs		/* != 0: can't do AST or SIR */
+	ldq	s0, GD_CURPROC(globalp)		/* save curproc in s0 */
+#ifdef SMP
+	ldl	s1, P_MD_KERNNEST(s0)
+	subl	s1, 1, s1			/* decrement nesting level */
+#endif
 
-	and	s1, ALPHA_PSL_USERMODE, t0	/* are we returning to user? */
-	beq	t0, Lrestoreregs		/* no: just return */
+	ldq	t1, (FRAME_PS * 8)(sp)		/* get the saved PS */
+	and	t1, ALPHA_PSL_USERMODE, t0	/* are we returning to user? */
+	beq	t0, Lkernelret			/* no: kernel return */
 
 	/* Handle any AST's or resched's. */
 	mov	sp, a0				/* only arg is frame */
 	CALL(ast)
+#ifdef SMP
+	br	Lrestoreregs
+#endif
+
+Lkernelret:
+#ifdef SMP
+	beq	s1, Lrestoreregs
+	stq	globalp, (FRAME_T7*8)(sp)	/* fixup globalp */
+#endif
 
 Lrestoreregs:
 	/* set the hae register if this process has specified a value */
-	ldq	t0, GD_CURPROC(globalp)
-	beq	t0, Lnohae
-	ldq	t1, P_MD_FLAGS(t0)
+	ldq	t1, P_MD_FLAGS(s0)
 	and	t1, MDP_HAEUSED
 	beq	t1, Lnohae
 	ldq	a0, P_MD_HAE(t0)
 	ldq	pv, chipset + CHIPSET_WRITE_HAE
 	CALL((pv))
 Lnohae:	
+#ifdef SMP
+	/* leave the kernel */
+	stl	s1, P_MD_KERNNEST(s0)
+#endif
 
 	/* restore the registers, and return */
 	bsr	ra, exception_restore_regs	/* jmp/CALL trashes pv/t12 */
diff --git a/sys/alpha/alpha/genassym.c b/sys/alpha/alpha/genassym.c
index 51046549ce3..03990ea51b3 100644
--- a/sys/alpha/alpha/genassym.c
+++ b/sys/alpha/alpha/genassym.c
@@ -84,6 +84,9 @@ ASSYM(P_ADDR, offsetof(struct proc, p_addr));
 ASSYM(P_MD_FLAGS, offsetof(struct proc, p_md.md_flags));
 ASSYM(P_MD_PCBPADDR, offsetof(struct proc, p_md.md_pcbpaddr));
 ASSYM(P_MD_HAE, offsetof(struct proc, p_md.md_hae));
+#ifdef SMP
+ASSYM(P_MD_KERNNEST, offsetof(struct proc, p_md.md_kernnest));
+#endif
 ASSYM(MDP_HAEUSED, MDP_HAEUSED);
 
 ASSYM(CHIPSET_WRITE_HAE, offsetof(struct alpha_chipset, write_hae));
diff --git a/sys/alpha/alpha/interrupt.c b/sys/alpha/alpha/interrupt.c
index c44eccf3b13..346b21cd544 100644
--- a/sys/alpha/alpha/interrupt.c
+++ b/sys/alpha/alpha/interrupt.c
@@ -91,12 +91,22 @@ interrupt(a0, a1, a2, framep)
 	struct trapframe *framep;
 {
 	struct proc *p;
+#ifdef SMP
+	critical_t s;
+#endif
 
 	/*
 	 * Find our per-cpu globals.
 	 */
+#ifdef SMP
+	s = critical_enter();
+#endif
 	globalp = (struct globaldata *) alpha_pal_rdval();
 	p = curproc;
+#ifdef SMP
+	p->p_md.md_kernnest++;
+	critical_exit(s);
+#endif
 	atomic_add_int(&p->p_intr_nesting_level, 1);
 #ifndef SMP
 	{
diff --git a/sys/alpha/alpha/machdep.c b/sys/alpha/alpha/machdep.c
index 78036218e1d..f6236690593 100644
--- a/sys/alpha/alpha/machdep.c
+++ b/sys/alpha/alpha/machdep.c
@@ -966,6 +966,9 @@ alpha_init(pfn, ptb, bim, bip, biv)
 		globaldata_init(globalp, alpha_pal_whami(), sz);
 		alpha_pal_wrval((u_int64_t) globalp);
 		PCPU_GET(next_asn) = 1;	/* 0 used for proc0 pmap */
+#ifdef SMP
+		proc0.p_md.md_kernnest = 1;
+#endif
 	}
 
 	/*
diff --git a/sys/alpha/alpha/trap.c b/sys/alpha/alpha/trap.c
index 1b08a7d128b..228c50b81bb 100644
--- a/sys/alpha/alpha/trap.c
+++ b/sys/alpha/alpha/trap.c
@@ -312,14 +312,24 @@ trap(a0, a1, a2, entry, framep)
 	u_int64_t ucode;
 	u_quad_t sticks;
 	int user;
+#ifdef SMP
+	critical_t s;
+#endif
 
 	/*
 	 * Find our per-cpu globals.
 	 */
+#ifdef SMP
+	s = critical_enter();
+#endif
 	globalp = (struct globaldata *) alpha_pal_rdval();
+	p = curproc;
+#ifdef SMP
+	p->p_md.md_kernnest++;
+	critical_exit(s);
+#endif
 
 	cnt.v_trap++;
-	p = curproc;
 	ucode = 0;
 	user = (framep->tf_regs[FRAME_PS] & ALPHA_PSL_USERMODE) != 0;
 	if (user)  {
@@ -704,11 +714,22 @@ syscall(code, framep)
 	u_quad_t sticks;
 	u_int64_t args[10];					/* XXX */
 	u_int hidden = 0, nargs;
+#ifdef SMP
+	critical_t s;
+#endif
 
 	/*
 	 * Find our per-cpu globals.
 	 */
+#ifdef SMP
+	s = critical_enter();
+#endif
 	globalp = (struct globaldata *) alpha_pal_rdval();
+	p = curproc;
+#ifdef SMP
+	p->p_md.md_kernnest++;
+	critical_exit(s);
+#endif
 	mtx_lock(&Giant);
 
 	framep->tf_regs[FRAME_TRAPARG_A0] = 0;
@@ -720,7 +741,6 @@ syscall(code, framep)
 #endif
 
 	cnt.v_syscall++;
-	p = curproc;
 	p->p_md.md_tf = framep;
 	opc = framep->tf_regs[FRAME_PC] - 4;
 	mtx_lock_spin(&sched_lock);
diff --git a/sys/alpha/include/proc.h b/sys/alpha/include/proc.h
index d003816ab0b..3a83c3942f7 100644
--- a/sys/alpha/include/proc.h
+++ b/sys/alpha/include/proc.h
@@ -50,6 +50,7 @@ struct mdproc {
 	struct mdbpt	md_sstep[2];	/* two single step breakpoints */
 	u_int64_t	md_hae;		/* user HAE register value */
 	void            *osf_sigtramp;  /* user-level signal trampoline */
+	u_int		md_kernnest;	/* nesting level in the kernel */
 };
 
 #define	MDP_FPUSED	0x0001		/* Process used the FPU */
diff --git a/sys/powerpc/powerpc/genassym.c b/sys/powerpc/powerpc/genassym.c
index 51046549ce3..03990ea51b3 100644
--- a/sys/powerpc/powerpc/genassym.c
+++ b/sys/powerpc/powerpc/genassym.c
@@ -84,6 +84,9 @@ ASSYM(P_ADDR, offsetof(struct proc, p_addr));
 ASSYM(P_MD_FLAGS, offsetof(struct proc, p_md.md_flags));
 ASSYM(P_MD_PCBPADDR, offsetof(struct proc, p_md.md_pcbpaddr));
 ASSYM(P_MD_HAE, offsetof(struct proc, p_md.md_hae));
+#ifdef SMP
+ASSYM(P_MD_KERNNEST, offsetof(struct proc, p_md.md_kernnest));
+#endif
 ASSYM(MDP_HAEUSED, MDP_HAEUSED);
 
 ASSYM(CHIPSET_WRITE_HAE, offsetof(struct alpha_chipset, write_hae));