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

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Date: Wed, 10 Jan 2024 13:28:36 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Ethan Zhao <haifeng.zhao@...ux.intel.com>, kevin.tian@...el.com,
 bhelgaas@...gle.com, dwmw2@...radead.org, will@...nel.org,
 robin.murphy@....com, lukas@...ner.de
Cc: baolu.lu@...ux.intel.com, 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 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?

Best regards,
baolu