linux-kernel - [RFC PATCH 1/9] tracepoint: call vmalloc_sync

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Date:   Thu,  9 Apr 2020 15:35:35 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, akpm@...ux-foundation.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "K . Prasad" <prasad@...ux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@...nel.org>, rostedt@...dmis.org,
        Alexei Starovoitov <ast@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: [RFC PATCH 1/9] tracepoint: call vmalloc_sync_mappings() on registration

Similarly to register_die_notifier(), tracepoints register callbacks
which can be invoked from execution contexts such as the page fault
handler and NMIs which should not generate a page fault. Those callbacks
can access virtual mappings and can be implemented in modules.

Calling vmalloc_sync_mappings() before registering a tracepoint callback
ensures that the virtual mappings are synchronized within each process
page tables, thus ensuring that no page fault will be triggered by the
callback.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/tracepoint.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 73956eaff8a9..82191a89c72e 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -14,6 +14,7 @@
 #include <linux/sched/signal.h>
 #include <linux/sched/task.h>
 #include <linux/static_key.h>
+#include <linux/vmalloc.h>
 
 extern tracepoint_ptr_t __start___tracepoints_ptrs[];
 extern tracepoint_ptr_t __stop___tracepoints_ptrs[];
@@ -308,6 +309,7 @@ int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
 	struct tracepoint_func tp_func;
 	int ret;
 
+	vmalloc_sync_mappings();
 	mutex_lock(&tracepoints_mutex);
 	tp_func.func = probe;
 	tp_func.data = data;
-- 
2.17.1