[RFC PATCH v8 5/5] iommu/vt-d: don't loop for timeout device-TLB invalidation request forever

[Ethan Zhao <haifeng.zhao@linux.intel.com>]

When the device-TLB invalidation (ATS invalidation) timeout happens, the
qi_submit_sync() will restart and loop for the invalidation request
forever till it is done, it will block another invalidation thread such
as the fq_timer to issue invalidation request, cause the system lockup as
following

#11 [fffffe0000b1def0] end_repeat_nmi at ffffffffaa6015f8

[exception RIP: native_queued_spin_lock_slowpath+92]

RIP: ffffffffa9d1025c RSP: ffffb202f268cdc8 RFLAGS: 00000002

RAX: 0000000000000101 RBX: ffffffffab36c2a0 RCX: 0000000000000000

RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffffab36c2a0

RBP: ffffffffab36c2a0 R8: 0000000000000001 R9: 0000000000000000

R10: 0000000000000010 R11: 0000000000000018 R12: 0000000000000000

R13: 0000000000000004 R14: ffff9e10d71b1c88 R15: ffff9e10d71b1980

ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018

--- ---

#12 [ffffb202f268cdc8] native_queued_spin_lock_slowpath at ffffffffa9d1025c

#13 [ffffb202f268cdc8] do_raw_spin_lock at ffffffffa9d121f1

#14 [ffffb202f268cdd8] _raw_spin_lock_irqsave at ffffffffaa51795b

#15 [ffffb202f268cdf8] iommu_flush_dev_iotlb at ffffffffaa20df48

#16 [ffffb202f268ce28] iommu_flush_iova at ffffffffaa20e182

#17 [ffffb202f268ce60] iova_domain_flush at ffffffffaa220e27

#18 [ffffb202f268ce70] fq_flush_timeout at ffffffffaa221c9d

#19 [ffffb202f268cea8] call_timer_fn at ffffffffa9d46661

#20 [ffffb202f268cf08] run_timer_softirq at ffffffffa9d47933

#21 [ffffb202f268cf98] __softirqentry_text_start at ffffffffaa8000e0

#22 [ffffb202f268cff0] asm_call_sysvec_on_stack at ffffffffaa60114f

--- ---

(the left part of exception see the hotplug case of ATS capable device)

If one endpoint device just no response to the device-TLB invalidation
request, but is not gone, it will bring down the whole system, to avoid
such case, don't try the timeout device-TLB request forever.

and as synchronous program model of current qi_submit_sync() implementation
we couldn't wait for the enough time as PCIe spec said 1min+50%, just break
it in current sync model. (PCIe spec r6.1, sec 10.3.1)

Signed-off-by: Ethan Zhao <haifeng.zhao@linux.intel.com>
---
 drivers/iommu/intel/dmar.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index 76903a8bf963..206ab0b7294f 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -1457,7 +1457,7 @@ int qi_submit_sync(struct intel_iommu *iommu, struct qi_desc *desc,
 	reclaim_free_desc(qi);
 	raw_spin_unlock_irqrestore(&qi->q_lock, flags);
 
-	if (rc == -EAGAIN)
+	if (rc == -EAGAIN && type !=QI_DIOTLB_TYPE && type != QI_DEIOTLB_TYPE)
 		goto restart;
 
 	if (iotlb_start_ktime)
-- 
2.31.1