[for-next][PATCH 17/18] tracing: load/unload page callbacks for simple_ring_buffer

[Steven Rostedt <rostedt@kernel.org>]

From: Vincent Donnefort <vdonnefort@google.com>

Add load/unload callback used for each admitted page in the ring-buffer.
This will be later useful for the pKVM hypervisor which uses a different
VA space and need to dynamically map/unmap the ring-buffer pages.

Link: https://patch.msgid.link/20260309162516.2623589-18-vdonnefort@google.com
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/simple_ring_buffer.h |  8 +++
 kernel/trace/simple_ring_buffer.c  | 91 +++++++++++++++++++++++-------
 2 files changed, 80 insertions(+), 19 deletions(-)

diff --git a/include/linux/simple_ring_buffer.h b/include/linux/simple_ring_buffer.h
index 2c4c0ae336bc..21aec556293e 100644
--- a/include/linux/simple_ring_buffer.h
+++ b/include/linux/simple_ring_buffer.h
@@ -54,4 +54,12 @@ int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer);
 
 int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buffer);
 
+int simple_ring_buffer_init_mm(struct simple_rb_per_cpu *cpu_buffer,
+			       struct simple_buffer_page *bpages,
+			       const struct ring_buffer_desc *desc,
+			       void *(*load_page)(unsigned long va),
+			       void (*unload_page)(void *va));
+
+void simple_ring_buffer_unload_mm(struct simple_rb_per_cpu *cpu_buffer,
+				  void (*unload_page)(void *));
 #endif
diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_buffer.c
index 15df9781411b..02af2297ae5a 100644
--- a/kernel/trace/simple_ring_buffer.c
+++ b/kernel/trace/simple_ring_buffer.c
@@ -71,7 +71,7 @@ static void simple_bpage_reset(struct simple_buffer_page *bpage)
 	local_set(&bpage->page->commit, 0);
 }
 
-static void simple_bpage_init(struct simple_buffer_page *bpage, unsigned long page)
+static void simple_bpage_init(struct simple_buffer_page *bpage, void *page)
 {
 	INIT_LIST_HEAD(&bpage->link);
 	bpage->page = (struct buffer_data_page *)page;
@@ -372,18 +372,15 @@ int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer)
 }
 EXPORT_SYMBOL_GPL(simple_ring_buffer_reset);
 
-/**
- * simple_ring_buffer_init - Init @cpu_buffer based on @desc
- * @cpu_buffer:	A simple_rb_per_cpu buffer to init, allocated by the caller.
- * @bpages:	Array of simple_buffer_pages, with as many elements as @desc->nr_page_va
- * @desc:	A ring_buffer_desc
- *
- * Returns 0 on success or -EINVAL if the content of @desc is invalid
- */
-int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_buffer_page *bpages,
-			    const struct ring_buffer_desc *desc)
+int simple_ring_buffer_init_mm(struct simple_rb_per_cpu *cpu_buffer,
+			       struct simple_buffer_page *bpages,
+			       const struct ring_buffer_desc *desc,
+			       void *(*load_page)(unsigned long va),
+			       void (*unload_page)(void *va))
 {
 	struct simple_buffer_page *bpage = bpages;
+	int ret = 0;
+	void *page;
 	int i;
 
 	/* At least 1 reader page and two pages in the ring-buffer */
@@ -392,15 +389,22 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 
 	memset(cpu_buffer, 0, sizeof(*cpu_buffer));
 
-	cpu_buffer->bpages = bpages;
+	cpu_buffer->meta = load_page(desc->meta_va);
+	if (!cpu_buffer->meta)
+		return -EINVAL;
 
-	cpu_buffer->meta = (void *)desc->meta_va;
 	memset(cpu_buffer->meta, 0, sizeof(*cpu_buffer->meta));
 	cpu_buffer->meta->meta_page_size = PAGE_SIZE;
 	cpu_buffer->meta->nr_subbufs = cpu_buffer->nr_pages;
 
 	/* The reader page is not part of the ring initially */
-	simple_bpage_init(bpage, desc->page_va[0]);
+	page = load_page(desc->page_va[0]);
+	if (!page) {
+		unload_page(cpu_buffer->meta);
+		return -EINVAL;
+	}
+
+	simple_bpage_init(bpage, page);
 	bpage->id = 0;
 
 	cpu_buffer->nr_pages = 1;
@@ -410,7 +414,13 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 	cpu_buffer->head_page = bpage + 1;
 
 	for (i = 1; i < desc->nr_page_va; i++) {
-		simple_bpage_init(++bpage, desc->page_va[i]);
+		page = load_page(desc->page_va[i]);
+		if (!page) {
+			ret = -EINVAL;
+			break;
+		}
+
+		simple_bpage_init(++bpage, page);
 
 		bpage->link.next = &(bpage + 1)->link;
 		bpage->link.prev = &(bpage - 1)->link;
@@ -419,6 +429,14 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 		cpu_buffer->nr_pages = i + 1;
 	}
 
+	if (ret) {
+		for (i--; i >= 0; i--)
+			unload_page((void *)desc->page_va[i]);
+		unload_page(cpu_buffer->meta);
+
+		return ret;
+	}
+
 	/* Close the ring */
 	bpage->link.next = &cpu_buffer->tail_page->link;
 	cpu_buffer->tail_page->link.prev = &bpage->link;
@@ -426,23 +444,58 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 	/* The last init'ed page points to the head page */
 	simple_bpage_set_head_link(bpage);
 
+	cpu_buffer->bpages = bpages;
+
 	return 0;
 }
-EXPORT_SYMBOL_GPL(simple_ring_buffer_init);
+
+static void *__load_page(unsigned long page)
+{
+	return (void *)page;
+}
+
+static void __unload_page(void *page) { }
 
 /**
- * simple_ring_buffer_unload - Prepare @cpu_buffer for deletion
- * @cpu_buffer:	A simple_rb_per_cpu that will be deleted.
+ * simple_ring_buffer_init - Init @cpu_buffer based on @desc
+ * @cpu_buffer:	A simple_rb_per_cpu buffer to init, allocated by the caller.
+ * @bpages:	Array of simple_buffer_pages, with as many elements as @desc->nr_page_va
+ * @desc:	A ring_buffer_desc
+ *
+ * Returns 0 on success or -EINVAL if the content of @desc is invalid
  */
-void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer)
+int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_buffer_page *bpages,
+			    const struct ring_buffer_desc *desc)
+{
+	return simple_ring_buffer_init_mm(cpu_buffer, bpages, desc, __load_page, __unload_page);
+}
+EXPORT_SYMBOL_GPL(simple_ring_buffer_init);
+
+void simple_ring_buffer_unload_mm(struct simple_rb_per_cpu *cpu_buffer,
+				  void (*unload_page)(void *))
 {
+	int p;
+
 	if (!simple_rb_loaded(cpu_buffer))
 		return;
 
 	simple_rb_enable_tracing(cpu_buffer, false);
 
+	unload_page(cpu_buffer->meta);
+	for (p = 0; p < cpu_buffer->nr_pages; p++)
+		unload_page(cpu_buffer->bpages[p].page);
+
 	cpu_buffer->bpages = NULL;
 }
+
+/**
+ * simple_ring_buffer_unload - Prepare @cpu_buffer for deletion
+ * @cpu_buffer:	A simple_rb_per_cpu that will be deleted.
+ */
+void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer)
+{
+	return simple_ring_buffer_unload_mm(cpu_buffer, __unload_page);
+}
 EXPORT_SYMBOL_GPL(simple_ring_buffer_unload);
 
 /**
-- 
2.51.0