The subbuf_ids field allows to point to a specific page from the
ring-buffer based on its ID. As a preparation or the upcoming
ring-buffer remote support, point this array to the buffer_page instead
of the buffer_data_page.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 2c157cb86989..e5846f8f3c07 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -519,7 +519,7 @@ struct ring_buffer_per_cpu {
 	unsigned int			mapped;
 	unsigned int			user_mapped;	/* user space mapping */
 	struct mutex			mapping_lock;
-	unsigned long			*subbuf_ids;	/* ID to subbuf VA */
+	struct buffer_page		**subbuf_ids;	/* ID to subbuf VA */
 	struct trace_buffer_meta	*meta_page;
 	struct ring_buffer_cpu_meta	*ring_meta;
 
@@ -7002,7 +7002,7 @@ static void rb_free_meta_page(struct ring_buffer_per_cpu *cpu_buffer)
 }
 
 static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
-				   unsigned long *subbuf_ids)
+				   struct buffer_page **subbuf_ids)
 {
 	struct trace_buffer_meta *meta = cpu_buffer->meta_page;
 	unsigned int nr_subbufs = cpu_buffer->nr_pages + 1;
@@ -7011,7 +7011,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
 	int id = 0;
 
 	id = rb_page_id(cpu_buffer, cpu_buffer->reader_page, id);
-	subbuf_ids[id++] = (unsigned long)cpu_buffer->reader_page->page;
+	subbuf_ids[id++] = cpu_buffer->reader_page;
 	cnt++;
 
 	first_subbuf = subbuf = rb_set_head_page(cpu_buffer);
@@ -7021,7 +7021,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
 		if (WARN_ON(id >= nr_subbufs))
 			break;
 
-		subbuf_ids[id] = (unsigned long)subbuf->page;
+		subbuf_ids[id] = subbuf;
 
 		rb_inc_page(&subbuf);
 		id++;
@@ -7030,7 +7030,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
 
 	WARN_ON(cnt != nr_subbufs);
 
-	/* install subbuf ID to kern VA translation */
+	/* install subbuf ID to bpage translation */
 	cpu_buffer->subbuf_ids = subbuf_ids;
 
 	meta->meta_struct_len = sizeof(*meta);
@@ -7186,13 +7186,15 @@ static int __rb_map_vma(struct ring_buffer_per_cpu *cpu_buffer,
 	}
 
 	while (p < nr_pages) {
+		struct buffer_page *subbuf;
 		struct page *page;
 		int off = 0;
 
 		if (WARN_ON_ONCE(s >= nr_subbufs))
 			return -EINVAL;
 
-		page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]);
+		subbuf = cpu_buffer->subbuf_ids[s];
+		page = virt_to_page((void *)subbuf->page);
 
 		for (; off < (1 << (subbuf_order)); off++, page++) {
 			if (p >= nr_pages)
@@ -7219,7 +7221,8 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 		    struct vm_area_struct *vma)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
-	unsigned long flags, *subbuf_ids;
+	struct buffer_page **subbuf_ids;
+	unsigned long flags;
 	int err;
 
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
@@ -7243,7 +7246,7 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu,
 	if (err)
 		return err;
 
-	/* subbuf_ids include the reader while nr_pages does not */
+	/* subbuf_ids includes the reader while nr_pages does not */
 	subbuf_ids = kcalloc(cpu_buffer->nr_pages + 1, sizeof(*subbuf_ids), GFP_KERNEL);
 	if (!subbuf_ids) {
 		rb_free_meta_page(cpu_buffer);
-- 
2.51.0.618.g983fd99d29-goog