In order to reduce the chance for the system becoming unresponsive due to event storms triggered by a misbehaving scsifront use the lateeoi irq binding for scsiback and unmask the event channel only just before leaving the event handling function.
In case of a ring protocol error don't issue an EOI in order to avoid the possibility to use that for producing an event storm. This at once will result in no further call of scsiback_irq_fn(), so the ring_error struct member can be dropped and scsiback_do_cmd_fn() can signal the protocol error via a negative return value.
This is part of XSA-332.
This is upstream commit 86991b6e7ea6c613b7692f65106076943449b6b7
Cc: stable@vger.kernel.org Reported-by: Julien Grall julien@xen.org Signed-off-by: Juergen Gross jgross@suse.com Reviewed-by: Jan Beulich jbeulich@suse.com Reviewed-by: Wei Liu wl@xen.org --- drivers/xen/xen-scsiback.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-)
diff --git a/drivers/xen/xen-scsiback.c b/drivers/xen/xen-scsiback.c index 14a3d4cbc2a7..1abc0a55b8d9 100644 --- a/drivers/xen/xen-scsiback.c +++ b/drivers/xen/xen-scsiback.c @@ -91,7 +91,6 @@ struct vscsibk_info { unsigned int irq;
struct vscsiif_back_ring ring; - int ring_error;
spinlock_t ring_lock; atomic_t nr_unreplied_reqs; @@ -722,7 +721,8 @@ static struct vscsibk_pend *prepare_pending_reqs(struct vscsibk_info *info, return pending_req; }
-static int scsiback_do_cmd_fn(struct vscsibk_info *info) +static int scsiback_do_cmd_fn(struct vscsibk_info *info, + unsigned int *eoi_flags) { struct vscsiif_back_ring *ring = &info->ring; struct vscsiif_request ring_req; @@ -739,11 +739,12 @@ static int scsiback_do_cmd_fn(struct vscsibk_info *info) rc = ring->rsp_prod_pvt; pr_warn("Dom%d provided bogus ring requests (%#x - %#x = %u). Halting ring processing\n", info->domid, rp, rc, rp - rc); - info->ring_error = 1; - return 0; + return -EINVAL; }
while ((rc != rp)) { + *eoi_flags &= ~XEN_EOI_FLAG_SPURIOUS; + if (RING_REQUEST_CONS_OVERFLOW(ring, rc)) break;
@@ -802,13 +803,16 @@ static int scsiback_do_cmd_fn(struct vscsibk_info *info) static irqreturn_t scsiback_irq_fn(int irq, void *dev_id) { struct vscsibk_info *info = dev_id; + int rc; + unsigned int eoi_flags = XEN_EOI_FLAG_SPURIOUS;
- if (info->ring_error) - return IRQ_HANDLED; - - while (scsiback_do_cmd_fn(info)) + while ((rc = scsiback_do_cmd_fn(info, &eoi_flags)) > 0) cond_resched();
+ /* In case of a ring error we keep the event channel masked. */ + if (!rc) + xen_irq_lateeoi(irq, eoi_flags); + return IRQ_HANDLED; }
@@ -829,7 +833,7 @@ static int scsiback_init_sring(struct vscsibk_info *info, grant_ref_t ring_ref, sring = (struct vscsiif_sring *)area; BACK_RING_INIT(&info->ring, sring, PAGE_SIZE);
- err = bind_interdomain_evtchn_to_irq(info->domid, evtchn); + err = bind_interdomain_evtchn_to_irq_lateeoi(info->domid, evtchn); if (err < 0) goto unmap_page;
@@ -1252,7 +1256,6 @@ static int scsiback_probe(struct xenbus_device *dev,
info->domid = dev->otherend_id; spin_lock_init(&info->ring_lock); - info->ring_error = 0; atomic_set(&info->nr_unreplied_reqs, 0); init_waitqueue_head(&info->waiting_to_free); info->dev = dev;