[PATCH v6 3/4] tracing: Use vmap_page_range() to map memmap ring buffer

[Steven Rostedt]

From: Steven Rostedt <rost...@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+gv41elms4wjqxhdnui6giddf...@mail.gmail.com/

Suggested-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rost...@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 e58b72e61573..f6531cd3176b 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 */
 
@@ -9796,29 +9797,27 @@ 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