linux-kernel - RE: [PATCH 2/3] iommu/vt-d: Drop stop marker messages

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Message-ID: <BN9PR11MB52767F7FCE2E82106ABDEBBA8CF39@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Mon, 18 Apr 2022 06:58:04 +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 2/3] iommu/vt-d: Drop stop marker messages

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Saturday, April 16, 2022 8:31 PM
> 
> 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. Hence, there's no need to
> report the stop-marker message in prq_event_thread(). The stop marker
> messages do not need a response. This drops stop marker messages silently
> if any of them is found in the page request queue.

The comment for iommu_queue_iopf says:

 * This module doesn't handle PCI PASID Stop Marker; IOMMU drivers must discard
 * them before reporting faults. A PASID Stop Marker (LRW = 0b100) doesn't
 * expect a response. It may be generated when disabling a PASID (issuing a
 * PASID stop request) by some PCI devices.

So obviously the current vt-d driver behavior violates that requirement.
Then should this be a bug fix instead?

> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reviewed-by: Jacob Pan <jacob.jun.pan@...ux.intel.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 d88af37c20ef..d1c42dfae6ca 100644
> --- a/drivers/iommu/intel/svm.c
> +++ b/drivers/iommu/intel/svm.c
> @@ -758,6 +758,10 @@ 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