linux-kernel - RE: [PATCH v2 6/7] iommu/vt-d: Add page request draining support

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Date:   Fri, 17 Apr 2020 02:27:49 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>
CC:     "Raj, Ashok" <ashok.raj@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2 6/7] iommu/vt-d: Add page request draining support

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Thursday, April 16, 2020 4:38 PM
> 
> Hi Kevin,
> 
> On 2020/4/15 19:10, Tian, Kevin wrote:
> > the completion of above sequence ensures that previous queued
> > page group responses are sent out and received by the endpoint
> > and vice versa all in-fly page requests from the endpoint are queued
> > in iommu page request queue. Then comes a problem - you didn't
> > wait for completion of those newly-queued requests and their
> > responses.
> 
> I thought about this again.
> 
> We do page request draining after PASID table entry gets torn down and
> the devTLB gets invalidated. At this point, if any new page request for
> this pasid comes in, IOMMU will generate an unrecoverable fault and
> response the device with IR (Invalid Request). IOMMU won't put this page
> request into the queue. [VT-d spec 7.4.1]

Non-coverable fault implies severe errors, so I don't see why we should
allow such thing happen when handling a normal situation. if you look at
the start of chapter 7:
--
Non-recoverable Faults: Requests that encounter non-recoverable 
address translation faults are aborted by the remapping hardware, 
and typically require a reset of the device (such as through a function-
level-reset) to recover and re-initialize the device to put it back into 
service.
--

> 
> Hence, we don't need to worry about the newly-queued requests here.
> 
> Best regards,
> Baolu

Thanks
Kevin