[PATCH v4 05/22] iommu: Add a timeout parameter for PRQ response

Jacob Pan
2019-06-09T13:41:47Z

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@linux.intel.com>
---
Documentation/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 138f666..b43f089 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 13b301c..64e87d5 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)
{
--
2.7.4