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Subject[PATCH v5 12/23] iommu: add a timeout parameter for prq response
Date
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 chooose
the timeout for IOMMU to track pending page requests.
This timeout mechanism is a basic safty 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@linux.intel.com>
---
Documentation/admin-guide/kernel-parameters.txt | 8 +++++++
drivers/iommu/iommu.c | 28 +++++++++++++++++++++++++
2 files changed, 36 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 11fc28e..5c1e836 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1718,6 +1718,14 @@
1 - Bypass the IOMMU for DMA.
unset - Use IOMMU translation for DMA.

+ 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 784e019..3a49b96 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -37,6 +37,18 @@
static struct kset *iommu_group_kset;
static DEFINE_IDA(iommu_group_ida);
static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA;
+/*
+ * 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_callback_data {
const struct iommu_ops *ops;
@@ -125,6 +137,22 @@ static int __init iommu_set_def_domain_type(char *str)
}
early_param("iommu.passthrough", iommu_set_def_domain_type);

+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)
{
--
2.7.4
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