[PATCH v3] vmcore: Add a kernel parameter vmcore_device_dump

[Kairui Song]

Since commit 2724273e8fd0 ("vmcore: add API to collect hardware dump in
second kernel"), drivers is allowed to add device related dump data to
vmcore as they want by using the device dump API. This have a potential
issue, the data is stored in memory, drivers may append too much data
and use too much memory. The vmcore is typically used in a kdump kernel
which runs in a pre-reserved small chunk of memory. So as a result it
will make kdump unusable at all due to OOM issues.

So introduce new vmcore_device_dump= kernel parameter, and disable
device dump by default. User can enable it only if device dump data is
required for debugging, and have the chance to increase the kdump
reserved memory accordingly before device dump fails kdump.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxx>

---

 Update from V2:
  - Improve related docs

 Update from V1:
  - Use bool parameter to turn it on/off instead of letting user give
    the size limit. Size of device dump is hard to determine.

 Documentation/admin-guide/kernel-parameters.txt | 14 ++++++++++++++
 fs/proc/Kconfig                                 |  6 ++++--
 fs/proc/vmcore.c                                | 13 +++++++++++++
 3 files changed, 31 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f6664b2e2..3706ad9e1d97 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5078,6 +5078,20 @@
 			decrease the size and leave more room for directly
 			mapped kernel RAM.
 
+	vmcore_device_dump=	[KNL,KDUMP]
+			Format: {"off" | "on"}
+			Depends on CONFIG_PROC_VMCORE_DEVICE_DUMP.
+			This parameter allows enable or disable device dump
+			for vmcore on kernel start-up.
+			Device dump allows drivers to append dump data to
+			vmcore so you can collect driver specified debug info.
+			Note that the drivers could append the data without
+			any limit, and the data is stored in memory, this may
+			bring a significant memory stress. If you want to turn
+			on this option, make sure you have reserved enough memory
+			with crashkernel= parameter.
+			default: off
+
 	vmcp_cma=nn[MG]	[KNL,S390]
 			Sets the memory size reserved for contiguous memory
 			allocations for the vmcp device driver.
diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
index 817c02b13b1d..1a7a38976bb0 100644
--- a/fs/proc/Kconfig
+++ b/fs/proc/Kconfig
@@ -56,8 +56,10 @@ config PROC_VMCORE_DEVICE_DUMP
 	  recovery kernel's initramfs to collect its underlying device
 	  snapshot.
 
-	  If you say Y here, the collected device dumps will be added
-	  as ELF notes to /proc/vmcore.
+	  If you say Y here, a new kernel parameter 'vmcore_device_dump'
+	  will be available. You can then enable device dump by passing
+	  'vmcore_device_dump=on' to kernel, the collected device dumps
+	  will be added as ELF notes to /proc/vmcore.
 
 config PROC_SYSCTL
 	bool "Sysctl support (/proc/sys)" if EXPERT
diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 3fe90443c1bb..d1b608b0efad 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -53,6 +53,8 @@ static struct proc_dir_entry *proc_vmcore;
 /* Device Dump list and mutex to synchronize access to list */
 static LIST_HEAD(vmcoredd_list);
 static DEFINE_MUTEX(vmcoredd_mutex);
+
+static bool vmcoredd_enabled;
 #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
 
 /* Device Dump Size */
@@ -1451,6 +1453,11 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
 	size_t data_size;
 	int ret;
 
+	if (!vmcoredd_enabled) {
+		pr_err_once("Device dump is disabled\n");
+		return -EINVAL;
+	}
+
 	if (!data || !strlen(data->dump_name) ||
 	    !data->vmcoredd_callback || !data->size)
 		return -EINVAL;
@@ -1502,6 +1509,12 @@ int vmcore_add_device_dump(struct vmcoredd_data *data)
 	return ret;
 }
 EXPORT_SYMBOL(vmcore_add_device_dump);
+
+static int __init vmcoredd_parse_cmdline(char *arg)
+{
+	return kstrtobool(arg, &vmcoredd_enabled);
+}
+__setup("vmcore_device_dump=", vmcoredd_parse_cmdline);
 #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
 
 /* Free all dumps in vmcore device dump list */
-- 
2.21.0