linux-kernel - RE: [RFC PATCH v9 5/5] iommu/vt-d: don't loop for timeout ATS Invalidation request forever

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Message-ID: <BN9PR11MB5276E70591021395F1ED90D28C9DA@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Fri, 29 Dec 2023 08:17:06 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Ethan Zhao <haifeng.zhao@...ux.intel.com>, "bhelgaas@...gle.com"
	<bhelgaas@...gle.com>, "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>, "will@...nel.org"
	<will@...nel.org>, "robin.murphy@....com" <robin.murphy@....com>,
	"lukas@...ner.de" <lukas@...ner.de>
CC: "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH v9 5/5] iommu/vt-d: don't loop for timeout ATS
 Invalidation request forever

> From: Ethan Zhao <haifeng.zhao@...ux.intel.com>
> Sent: Thursday, December 28, 2023 9:10 PM
> 
> On 12/28/2023 4:38 PM, Tian, Kevin wrote:
> >> From: Ethan Zhao <haifeng.zhao@...ux.intel.com>
> >> Sent: Thursday, December 28, 2023 8:17 AM
> >>
> >>
> >> -	if (rc == -EAGAIN)
> >> +	if (rc == -EAGAIN && type !=QI_DIOTLB_TYPE && type !=
> >> QI_DEIOTLB_TYPE)
> >>   		goto restart;
> >>
> > this change is moot.
> >
> > -EAGAIN is set only when hardware detects a ATS invalidation completion
> > timeout in qi_check_fault(). so above just essentially kills the restart logic.
> 
> This change is intended to break the restar login when device-TLB
> 
> invalidation timeout happens, we don't know how long the ITE took
> 
> if the device is just no reponse.

if in the end the agreement is to remove the restart logic, then do it.

it's not good to introduce a change which essentially kills the restart
logic but still keeps the related code.