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

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Message-ID: <acf26559-49d2-653c-156d-3ef383b43879@linux.intel.com>
Date:   Thu, 16 Apr 2020 16:38:19 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     baolu.lu@...ux.intel.com, "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

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]

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

Best regards,
baolu