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

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Message-Id: <20220416123049.879969-3-baolu.lu@linux.intel.com>
Date:   Sat, 16 Apr 2022 20:30:48 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob jun Pan <jacob.jun.pan@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Liu Yi L <yi.l.liu@...el.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: [PATCH 2/3] iommu/vt-d: Drop stop marker messages

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.

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