tracing: Add option to use memmapped memory for trace boot instance

Add an option to the trace_instance kernel command line parameter that
allows it to use the reserved memory from memmap boot parameter.

  memmap=12M$0x284500000 trace_instance=boot_mapped@0x284500000:12M

The above will reserves 12 megs at the physical address 0x284500000.
The second parameter will create a "boot_mapped" instance and use the
memory reserved as the memory for the ring buffer.

That will create an instance called "boot_mapped":

  /sys/kernel/tracing/instances/boot_mapped

Note, because the ring buffer is using a defined memory ranged, it will
act just like a memory mapped ring buffer. It will not have a snapshot
buffer, as it can't swap out the buffer. The snapshot files as well as any
tracers that uses a snapshot will not be present in the boot_mapped
instance.

Link: https://lkml.kernel.org/r/20240612232026.329660169@goodmis.org

Cc: linux-mm@kvack.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>

Documentation/admin-guide/kernel-parameters.txt

@@ -6754,6 +6754,15 @@
 			the same thing would happen if it was left off). The irq_handler_entry
 			event, and all events under the "initcall" system.
 
+			If memory has been reserved (see memmap for x86), the instance
+			can use that memory:
+
+				memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M
+
+			The above will create a "boot_map" instance that uses the physical
+			memory at 0x284500000 that is 12Megs. The per CPU buffers of that
+			instance will be split up accordingly.
+
 	trace_options=[option-list]
 			[FTRACE] Enable or disable tracer options at boot.
 			The option-list is a comma delimited list of options

kernel/trace/trace.c

@@ -9504,6 +9504,31 @@ out_unlock:
 	return ret;
 }
 
+static u64 map_pages(u64 start, u64 size)
+{
+	struct page **pages;
+	phys_addr_t page_start;
+	unsigned int page_count;
+	unsigned int i;
+	void *vaddr;
+
+	page_count = DIV_ROUND_UP(size, PAGE_SIZE);
+
+	page_start = start;
+	pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
+	if (!pages)
+		return 0;
+
+	for (i = 0; i < page_count; i++) {
+		phys_addr_t addr = page_start + i * PAGE_SIZE;
+		pages[i] = pfn_to_page(addr >> PAGE_SHIFT);
+	}
+	vaddr = vmap(pages, page_count, VM_MAP, PAGE_KERNEL);
+	kfree(pages);
+
+	return (u64)(unsigned long)vaddr;
+}
+
 /**
  * trace_array_get_by_name - Create/Lookup a trace array, given its name.
  * @name: The name of the trace array to be looked up/created.
@@ -10350,6 +10375,7 @@ __init static void enable_instances(void)
 {
 	struct trace_array *tr;
 	char *curr_str;
+	char *name;
 	char *str;
 	char *tok;
 
@@ -10358,18 +10384,55 @@ __init static void enable_instances(void)
 	str = boot_instance_info;
 
 	while ((curr_str = strsep(&str, "\t"))) {
+		unsigned long start = 0;
+		unsigned long size = 0;
+		unsigned long addr = 0;
 
 		tok = strsep(&curr_str, ",");
-
-		if (IS_ENABLED(CONFIG_TRACER_MAX_TRACE))
-			do_allocate_snapshot(tok);
-
-		tr = trace_array_get_by_name(tok, NULL);
-		if (!tr) {
-			pr_warn("Failed to create instance buffer %s\n", curr_str);
+		name = strsep(&tok, "@");
+		if (tok) {
+			start = memparse(tok, &tok);
+			if (!start) {
+				pr_warn("Tracing: Invalid boot instance address for %s\n",
+					name);
 				continue;
 			}
-		/* Allow user space to delete it */
+		}
+
+		if (start) {
+			if (*tok != ':') {
+				pr_warn("Tracing: No size specified for instance %s\n", name);
+				continue;
+			}
+			tok++;
+			size = memparse(tok, &tok);
+			if (!size) {
+				pr_warn("Tracing: Invalid boot instance size for %s\n",
+					name);
+				continue;
+			}
+			addr = map_pages(start, size);
+			if (addr) {
+				pr_info("Tracing: mapped boot instance %s at physical memory 0x%lx of size 0x%lx\n",
+					name, start, size);
+			} else {
+				pr_warn("Tracing: Failed to map boot instance %s\n", name);
+				continue;
+			}
+		} else {
+			/* Only non mapped buffers have snapshot buffers */
+			if (IS_ENABLED(CONFIG_TRACER_MAX_TRACE))
+				do_allocate_snapshot(name);
+		}
+
+		tr = trace_array_create_systems(name, NULL, addr, size);
+		if (!tr) {
+			pr_warn("Tracing: Failed to create instance buffer %s\n", curr_str);
+			continue;
+		}
+
+		/* Only allow non mapped buffers to be deleted */
+		if (!start)
 			trace_array_put(tr);
 
 		while ((tok = strsep(&curr_str, ","))) {