4.9-stable review patch. If anyone has any objections, please let me know.
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From: Juergen Gross jgross@suse.com
commit d3132b3860f6cf35ff7609a76bbcdbb814bd027c upstream.
Commit a856531951dc80 ("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: a856531951dc80 ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/xen/spinlock.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-)
--- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -8,6 +8,7 @@ #include <linux/log2.h> #include <linux/gfp.h> #include <linux/slab.h> +#include <linux/atomic.h>
#include <asm/paravirt.h>
@@ -19,6 +20,7 @@
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;
#include <asm/qspinlock.h> @@ -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)