linux-kernel - Re: [RFC PATCH v10 5/5] iommu/vt-d: don't loop for timeout ATS Invalidation request forever

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Message-ID: <53c563ad-b47b-4962-abc7-f0da3a7181d6@linux.intel.com>
Date: Wed, 10 Jan 2024 16:40:02 +0800
From: Ethan Zhao <haifeng.zhao@...ux.intel.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>, kevin.tian@...el.com,
 bhelgaas@...gle.com, dwmw2@...radead.org, will@...nel.org,
 robin.murphy@....com, lukas@...ner.de
Cc: linux-pci@...r.kernel.org, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v10 5/5] iommu/vt-d: don't loop for timeout ATS
 Invalidation request forever


On 1/10/2024 1:28 PM, Baolu Lu wrote:
> On 12/29/23 1:05 AM, Ethan Zhao wrote:
>> When the ATS Invalidation request 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
>>
>> [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
>>
>> (the left part of exception see the hotplug case of ATS capable device)
>>
>> If one endpoint device just no response to the ATS Invalidation request,
>> but is not gone, it will bring down the whole system, to avoid such
>> case, don't try the timeout ATS Invalidation request forever.
>>
>> Signed-off-by: Ethan Zhao <haifeng.zhao@...ux.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 0a8d628a42ee..9edb4b44afca 100644
>> --- a/drivers/iommu/intel/dmar.c
>> +++ b/drivers/iommu/intel/dmar.c
>> @@ -1453,7 +1453,7 @@ 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)
>
> Above is also unnecessary if qi_check_fault() returns -ETIMEDOUT,
> instead of -EAGAIN. Or did I miss anything?

It is pro if we fold it into qi_check_fault(), the con is we have to add

more parameter to qi_check_fault(), no need check invalidation type

of QI_DIOTLB_TYPE&QI_DEIOTLB_TYPE in qi_check_fault() ?


Thanks,

Ethan

>
> Best regards,
> baolu