iommu: Add a timeout parameter for PRQ response

maillist inclusion
category: feature
bugzilla: 51855
CVE: NA

Reference: https://jpbrucker.net/git/linux/commit/?h=sva/2021-03-01&id=2c56ef21daed0cd65da9b4907ce4b84c56ca7c1c

---------------------------------------------

When an I/O page request is processed outside the 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: NJacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: NLijun Fang <fanglijun3@huawei.com>
Reviewed-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -2019,6 +2019,14 @@
 			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.

drivers/iommu/iommu.c

@@ -32,6 +32,19 @@ static unsigned int iommu_def_domain_type __read_mostly;
 static bool iommu_dma_strict __read_mostly = true;
 static u32 iommu_cmd_line __read_mostly;
 
+/*
+ * Timeout to wait for page response of a pending page request. This is
+ * intended as a basic safety 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;
@@ -329,6 +342,26 @@ static int __init iommu_dma_setup(char *str)
 }
 early_param("iommu.strict", iommu_dma_setup);
 
+static int __init iommu_set_prq_timeout(char *str)
+{
+	int ret;
+	unsigned long timeout;
+
+	if (!str)
+		return -EINVAL;
+
+	ret = kstrtoul(str, 10, &timeout);
+	if (ret)
+		return ret;
+	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)
 {