[v3,3/5] tracing: Use vmap_page_range() to map memmap ring buffer

Commit Message

Steven Rostedt April 1, 2025, 8:25 p.m. UTC

From: Steven Rostedt <[e-mail]>

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-=[e-mail]/

Suggested-by: Linus Torvalds <[e-mail]>
Signed-off-by: Steven Rostedt (Google) <[e-mail]>
---
 kernel/trace/trace.c | 35 +++++++++++++++++------------------
 1 file changed, 17 insertions(+), 18 deletions(-)

Comments

Steven Rostedt April 1, 2025, 9:41 p.m. UTC | #1

On Tue, 01 Apr 2025 16:25:52 -0400
Steven Rostedt <[e-mail]> wrote:

> -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;
> +        unsigned long vmap_start, vmap_end;

Bah, looks like I have whitespace issues. Will send an update to fix this
and the change log for patch 4.

> +	struct vm_struct *area;
> +	int ret;
>

Patch

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index e33f3b092e2e..1d7d2b772a74 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 */
 
@@ -9803,29 +9804,27 @@  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;
+        unsigned long vmap_start, vmap_end;
+	struct vm_struct *area;
+	int ret;
 
-	page_count = DIV_ROUND_UP(size, PAGE_SIZE);
+        area = get_vm_area(size, VM_IOREMAP);
+        if (!area)
+                return 0;
 
-	page_start = start;
-	pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
-	if (!pages)
-		return 0;
+        vmap_start = (unsigned long) area->addr;
+        vmap_end = vmap_start + size;
 
-	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);
+        ret = vmap_page_range(vmap_start, vmap_end,
+			      start, pgprot_nx(PAGE_KERNEL));
+        if (ret < 0) {
+                free_vm_area(area);
+                return 0;
+        }
 
-	return (u64)(unsigned long)vaddr;
+	return (u64)vmap_start;
 }
 
 /**