linux-kernel - RE: [PATCH v2 3/4] iommu/vt-d: Drop stop marker messages

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Date:   Fri, 22 Apr 2022 03:05:50 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
CC:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: RE: [PATCH v2 3/4] iommu/vt-d: Drop stop marker messages

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Thursday, April 21, 2022 7:36 PM
> 
> The page fault handling framework in the IOMMU core explicitly states
> that it doesn't handle PCI PASID Stop Marker and the IOMMU drivers must
> discard them before reporting faults. This handles Stop Marker messages
> in prq_event_thread() before reporting events to the core.
> 
> The VT-d driver explicitly drains the pending page requests when a CPU
> page table (represented by a mm struct) is unbound from a PASID according
> to the procedures defined in the VT-d spec. The Stop Marker messages do
> not need a response. Hence, it is safe to drop the Stop Marker messages
> silently if any of them is found in the page request queue.
> 
> Fixes: d5b9e4bfe0d88 ("iommu/vt-d: Report prq to io-pgfault framework")
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reviewed-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>

Reviewed-by: Kevin Tian <kevin.tian@...el.com>

> ---
>  drivers/iommu/intel/svm.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
> index c720d1be992d..0741ec165673 100644
> --- a/drivers/iommu/intel/svm.c
> +++ b/drivers/iommu/intel/svm.c
> @@ -760,6 +760,10 @@ static irqreturn_t prq_event_thread(int irq, void *d)
>  			goto bad_req;
>  		}
> 
> +		/* Drop Stop Marker message. No need for a response. */
> +		if (unlikely(req->lpig && !req->rd_req && !req->wr_req))
> +			goto prq_advance;
> +
>  		if (!svm || svm->pasid != req->pasid) {
>  			/*
>  			 * It can't go away, because the driver is not
> permitted
> --
> 2.25.1