linux-kernel - [PATCH] iommu/arm-smmu-v3: Fix event queue overflow acknowledgment

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Message-ID: <20230308092048.71390-1-krckatom@amazon.de>
Date:   Wed, 8 Mar 2023 09:20:47 +0000
From:   Tomas Krcka <krckatom@...zon.de>
To:     <linux-arm-kernel@...ts.infradead.org>
CC:     Tomas Krcka <krckatom@...zon.de>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] iommu/arm-smmu-v3: Fix event queue overflow acknowledgment

When an overflow occurs in the event queue, the SMMU toggles overflow
flag OVFLG in the PROD register.
The evtq thread is supposed to acknowledge the overflow flag by toggling
flag OVACKFLG in the CONS register, otherwise the overflow condition is
still active (OVFLG != OVACKFLG).

Currently the acknowledge register is toggled after clearing the event
queue but is never propagated to the hardware. It would be done next
time when executing evtq thread.

The SMMU still adds elements to the queue when the overflow condition is
active but any subsequent overflow information after clearing the event
queue will be lost.

This change keeps the SMMU in sync as it's expected by design.

Signed-off-by: Tomas Krcka <krckatom@...zon.de>
Suggested-by: KarimAllah Ahmed <karahmed@...zon.de>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index f2425b0f0cd6..acc1ff5ff69b 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1579,6 +1579,7 @@ static irqreturn_t arm_smmu_evtq_thread(int irq, void *dev)
 	/* Sync our overflow flag, as we believe we're up to speed */
 	llq->cons = Q_OVF(llq->prod) | Q_WRP(llq, llq->cons) |
 		    Q_IDX(llq, llq->cons);
+	queue_sync_cons_out(q);
 	return IRQ_HANDLED;
 }

-- 
2.39.1

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