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Date:   Sun, 26 May 2019 18:09:40 +0200
From:   Eric Auger <eric.auger@...hat.com>
To:     eric.auger.pro@...il.com, eric.auger@...hat.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu, joro@...tes.org,
        alex.williamson@...hat.com, jacob.jun.pan@...ux.intel.com,
        yi.l.liu@...el.com, jean-philippe.brucker@....com,
        will.deacon@....com, robin.murphy@....com
Cc:     kevin.tian@...el.com, ashok.raj@...el.com, marc.zyngier@....com,
        peter.maydell@...aro.org, vincent.stehle@....com
Subject: [PATCH v8 05/29] iommu: Add a timeout parameter for PRQ response

From: Jacob Pan <jacob.jun.pan@...ux.intel.com>

When an IO page request is processed outside IOMMU subsystem, response
can be delayed or lost. Add a tunable setup parameter such that user can
choose the timeout for IOMMU to track pending page requests.

This timeout mechanism is a basic safety net which can be implemented in
conjunction with credit based or device level page response exception
handling.

Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
---
 .../admin-guide/kernel-parameters.txt         |  8 +++++
 drivers/iommu/iommu.c                         | 29 +++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f6664b2e2..b43f0893d252 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1813,6 +1813,14 @@
 			1 - Bypass the IOMMU for DMA.
 			unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
 
+	iommu.prq_timeout=
+			Timeout in seconds to wait for page response
+			of a pending page request.
+			Format: <integer>
+			Default: 10
+			0 - no timeout tracking
+			1 to 100 - allowed range
+
 	io7=		[HW] IO7 for Marvel based alpha systems
 			See comment before marvel_specify_io7 in
 			arch/alpha/kernel/core_marvel.c.
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 13b301cfb10f..64e87d56f471 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -45,6 +45,19 @@ static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
 #endif
 static bool iommu_dma_strict __read_mostly = true;
 
+/*
+ * Timeout to wait for page response of a pending page request. This is
+ * intended as a basic safty net in case a pending page request is not
+ * responded for an exceptionally long time. Device may also implement
+ * its own protection mechanism against this exception.
+ * Units are in jiffies with a range between 1 - 100 seconds equivalent.
+ * Default to 10 seconds.
+ * Setting 0 means no timeout tracking.
+ */
+#define IOMMU_PAGE_RESPONSE_MAX_TIMEOUT (HZ * 100)
+#define IOMMU_PAGE_RESPONSE_DEF_TIMEOUT (HZ * 10)
+static unsigned long prq_timeout = IOMMU_PAGE_RESPONSE_DEF_TIMEOUT;
+
 struct iommu_group {
 	struct kobject kobj;
 	struct kobject *devices_kobj;
@@ -157,6 +170,22 @@ static int __init iommu_dma_setup(char *str)
 }
 early_param("iommu.strict", iommu_dma_setup);
 
+static int __init iommu_set_prq_timeout(char *str)
+{
+	unsigned long timeout;
+
+	if (!str)
+		return -EINVAL;
+	timeout = simple_strtoul(str, NULL, 0);
+	timeout = timeout * HZ;
+	if (timeout > IOMMU_PAGE_RESPONSE_MAX_TIMEOUT)
+		return -EINVAL;
+	prq_timeout = timeout;
+
+	return 0;
+}
+early_param("iommu.prq_timeout", iommu_set_prq_timeout);
+
 static ssize_t iommu_group_attr_show(struct kobject *kobj,
 				     struct attribute *__attr, char *buf)
 {
-- 
2.20.1

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