xen: fix xen_qlock_wait()

jgross1 · jgross1 · commit d3132b3860f6 · 2018-11-09T16:37:27.000+01:00
Commit a856531 ("xen: make xen_qlock_wait() nestable") introduced a regression for Xen guests running fully virtualized (HVM or PVH mode). The Xen hypervisor wouldn't return from the poll hypercall with interrupts disabled in case of an interrupt (for PV guests it does). So instead of disabling interrupts in xen_qlock_wait() use a nesting counter to avoid calling xen_clear_irq_pending() in case xen_qlock_wait() is nested. Fixes: a856531 ("xen: make xen_qlock_wait() nestable") Cc: stable@vger.kernel.org Reported-by: Sander Eikelenboom <linux@eikelenboom.it> Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Tested-by: Sander Eikelenboom <linux@eikelenboom.it> Signed-off-by: Juergen Gross <jgross@suse.com>
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
@@ -9,6 +9,7 @@
 #include <linux/log2.h>
 #include <linux/gfp.h>
 #include <linux/slab.h>
+#include <linux/atomic.h>
 
 #include <asm/paravirt.h>
 #include <asm/qspinlock.h>
@@ -21,6 +22,7 @@
 
 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
 static DEFINE_PER_CPU(char *, irq_name);
+static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
 static bool xen_pvspin = true;
 
 static void xen_qlock_kick(int cpu)
@@ -39,25 +41,25 @@ static void xen_qlock_kick(int cpu)
  */
 static void xen_qlock_wait(u8 *byte, u8 val)
 {
-	unsigned long flags;
 	int irq = __this_cpu_read(lock_kicker_irq);
+	atomic_t *nest_cnt = this_cpu_ptr(&xen_qlock_wait_nest);
 
 	/* If kicker interrupts not initialized yet, just spin */
 	if (irq == -1 || in_nmi())
 		return;
 
-	/* Guard against reentry. */
-	local_irq_save(flags);
+	/* Detect reentry. */
+	atomic_inc(nest_cnt);
 
-	/* If irq pending already clear it. */
-	if (xen_test_irq_pending(irq)) {
+	/* If irq pending already and no nested call clear it. */
+	if (atomic_read(nest_cnt) == 1 && xen_test_irq_pending(irq)) {
 		xen_clear_irq_pending(irq);
 	} else if (READ_ONCE(*byte) == val) {
 		/* Block until irq becomes pending (or a spurious wakeup) */
 		xen_poll_irq(irq);
 	}
 
-	local_irq_restore(flags);
+	atomic_dec(nest_cnt);
 }
 
 static irqreturn_t dummy_handler(int irq, void *dev_id)
