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From:   gregkh@linuxfoundation.org
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Kevin Tian <kevin.tian@intel.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <jroedel@suse.de>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.11 130/306] iommu/vt-d: Clear PRQ overflow only when PRQ is empty
Date:   Mon, 15 Mar 2021 14:53:13 +0100
Message-Id: <20210315135512.047519645@linuxfoundation.org>
In-Reply-To: <20210315135507.611436477@linuxfoundation.org>
References: <20210315135507.611436477@linuxfoundation.org>
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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

From: Lu Baolu <baolu.lu@linux.intel.com>

[ Upstream commit 28a77185f1cd0650b664f54614143aaaa3a7a615 ]

It is incorrect to always clear PRO when it's set w/o first checking
whether the overflow condition has been cleared. Current code assumes
that if an overflow condition occurs it must have been cleared by earlier
loop. However since the code runs in a threaded context, the overflow
condition could occur even after setting the head to the tail under some
extreme condition. To be sane, we should read both head/tail again when
seeing a pending PRO and only clear PRO after all pending PRs have been
handled.

Suggested-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/linux-iommu/MWHPR11MB18862D2EA5BD432BF22D99A48CA09@MWHPR11MB1886.namprd11.prod.outlook.com/
Link: https://lore.kernel.org/r/20210126080730.2232859-2-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iommu/intel/svm.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 18a9f05df407..b3bcd6dec93e 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -1079,8 +1079,17 @@ static irqreturn_t prq_event_thread(int irq, void *d)
 	 * Clear the page request overflow bit and wake up all threads that
 	 * are waiting for the completion of this handling.
 	 */
-	if (readl(iommu->reg + DMAR_PRS_REG) & DMA_PRS_PRO)
-		writel(DMA_PRS_PRO, iommu->reg + DMAR_PRS_REG);
+	if (readl(iommu->reg + DMAR_PRS_REG) & DMA_PRS_PRO) {
+		pr_info_ratelimited("IOMMU: %s: PRQ overflow detected\n",
+				    iommu->name);
+		head = dmar_readq(iommu->reg + DMAR_PQH_REG) & PRQ_RING_MASK;
+		tail = dmar_readq(iommu->reg + DMAR_PQT_REG) & PRQ_RING_MASK;
+		if (head == tail) {
+			writel(DMA_PRS_PRO, iommu->reg + DMAR_PRS_REG);
+			pr_info_ratelimited("IOMMU: %s: PRQ overflow cleared",
+					    iommu->name);
+		}
+	}
 
 	if (!completion_done(&iommu->prq_complete))
 		complete(&iommu->prq_complete);
-- 
2.30.1