[PATCH v4 3/4] tracing: Use vmap_page_range() to map memmap ring buffer

[Steven Rostedt <rostedt@goodmis.org>]

From: Steven Rostedt <rostedt@goodmis.org>

The code to map the physical memory retrieved by memmap currently
allocates an array of pages to cover the physical memory and then calls
vmap() to map it to a virtual address. Instead of using this temporary
array of struct page descriptors, simply use vmap_page_range() that can
directly map the contiguous physical memory to a virtual address.

Link: https://lore.kernel.org/all/CAHk-=whUOfVucfJRt7E0AH+GV41ELmS4wJqxHDnui6Giddfkzw@mail.gmail.com/

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d960f80701bd..24852bd4fc01 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -50,6 +50,7 @@
 #include <linux/irq_work.h>
 #include <linux/workqueue.h>
 #include <linux/sort.h>
+#include <linux/io.h> /* vmap_page_range() */
 
 #include <asm/setup.h> /* COMMAND_LINE_SIZE */
 
@@ -9817,29 +9818,27 @@ static int instance_mkdir(const char *name)
 	return ret;
 }
 
-static u64 map_pages(u64 start, u64 size)
+static u64 map_pages(unsigned long start, unsigned long 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);
+	unsigned long vmap_start, vmap_end;
+	struct vm_struct *area;
+	int ret;
 
-	page_start = start;
-	pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
-	if (!pages)
+	area = get_vm_area(size, VM_IOREMAP);
+	if (!area)
 		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);
+	vmap_start = (unsigned long) area->addr;
+	vmap_end = vmap_start + size;
+
+	ret = vmap_page_range(vmap_start, vmap_end,
+			      start, pgprot_nx(PAGE_KERNEL));
+	if (ret < 0) {
+		free_vm_area(area);
+		return 0;
 	}
-	vaddr = vmap(pages, page_count, VM_MAP, PAGE_KERNEL);
-	kfree(pages);
 
-	return (u64)(unsigned long)vaddr;
+	return (u64)vmap_start;
 }
 
 /**
-- 
2.47.2