Explicitly switch to the new TSS by updating the current CPU's TSS selector

and reloading it in i386_extend_pcb() rather than trying to force a context
switch to reload the TSS via the TDF_NEEDRESCHED flag.  Optimizations to
avoid calling cpu_switch() when the new thread was identical to the old
thread defeated the attempt to force a TSS reload.  Explicitly loading the
new TSS is what we really want to do anyway.

PR:		i386/84842
Reported by:	Alexander Best arundel at h3c dot de
MFC after:	1 week
Reviewed by:	bde (mostly)

2 files changed, 7 insertions, 4 deletions

diff --git a/sys/i386/i386/sys_machdep.c b/sys/i386/i386/sys_machdep.c
index 467ee65..23e8144 100644
--- a/sys/i386/i386/sys_machdep.c
+++ b/sys/i386/i386/sys_machdep.c
@@ -263,13 +263,15 @@ i386_extend_pcb(struct thread *td)
 	ssd.ssd_limit -= ((unsigned)&ext->ext_tss - (unsigned)ext);
 	ssdtosd(&ssd, &ext->ext_tssd);
 
-	KASSERT(td->td_proc == curthread->td_proc, ("giving TSS to !curproc"));
+	KASSERT(td == curthread, ("giving TSS to !curthread"));
 	KASSERT(td->td_pcb->pcb_ext == 0, ("already have a TSS!"));
+
+	/* Switch to the new TSS. */
 	mtx_lock_spin(&sched_lock);
 	td->td_pcb->pcb_ext = ext;
-	
-	/* switch to the new TSS after syscall completes */
-	td->td_flags |= TDF_NEEDRESCHED;
+	private_tss |= PCPU_GET(cpumask);
+	*PCPU_GET(tss_gdt) = ext->ext_tssd;
+	ltr(GSEL(GPROC0_SEL, SEL_KPL));
 	mtx_unlock_spin(&sched_lock);
 
 	return 0;
diff --git a/sys/i386/include/pcb_ext.h b/sys/i386/include/pcb_ext.h
index cf5a911..81e1bed 100644
--- a/sys/i386/include/pcb_ext.h
+++ b/sys/i386/include/pcb_ext.h
@@ -44,6 +44,7 @@ struct pcb_ext {
 };
 
 #ifdef _KERNEL
+extern int private_tss;
 
 int i386_extend_pcb(struct thread *);