ring-buffer: Add ring_buffer_alloc_range()

In preparation to allowing the trace ring buffer to be allocated in a
range of memory that is persistent across reboots, add
ring_buffer_alloc_range(). It takes a contiguous range of memory and will
split it up evenly for the per CPU ring buffers.

If there's not enough memory to handle all CPUs with the minimum size, it
will fail to allocate the ring buffer.

Link: https://lkml.kernel.org/r/20240612232025.363998725@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vineeth Pillai <vineeth@bitbyteword.org>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

include/linux/ring_buffer.h

@@ -89,6 +89,11 @@ void ring_buffer_discard_commit(struct trace_buffer *buffer,
 struct trace_buffer *
 __ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *key);
 
+struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flags,
+					       int order, unsigned long start,
+					       unsigned long range_size,
+					       struct lock_class_key *key);
+
 /*
  * Because the ring buffer is generic, if other users of the ring buffer get
  * traced by ftrace, it can produce lockdep warnings. We need to keep each
@@ -100,6 +105,18 @@ __ring_buffer_alloc(unsigned long size, unsigned flags, struct lock_class_key *k
 	__ring_buffer_alloc((size), (flags), &__key);	\
 })
 
+/*
+ * Because the ring buffer is generic, if other users of the ring buffer get
+ * traced by ftrace, it can produce lockdep warnings. We need to keep each
+ * ring buffer's lock class separate.
+ */
+#define ring_buffer_alloc_range(size, flags, order, start, range_size)	\
+({									\
+	static struct lock_class_key __key;				\
+	__ring_buffer_alloc_range((size), (flags), (order), (start),	\
+				  (range_size), &__key);		\
+})
+
 typedef bool (*ring_buffer_cond_fn)(void *data);
 int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full,
 		     ring_buffer_cond_fn cond, void *data);