powerpc/powernv/memtrace: Allow mmaping trace buffers

Let the memory removed from the linear mapping to be used for the trace
buffers be mmaped. This is a useful way of providing cache-inhibited
memory for the alignment_handler selftest.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
[mpe: make memtrace_mmap() static as noticed by lkp@intel.com]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210225032108.1458352-1-jniethe5@gmail.com

diff --git a/arch/powerpc/platforms/powernv/memtrace.c b/arch/powerpc/platforms/powernv/memtrace.c
index 019669e..71c1262 100644 (file)
--- a/arch/powerpc/platforms/powernv/memtrace.c
+++ b/arch/powerpc/platforms/powernv/memtrace.c
@@ -46,10 +46,26 @@ static ssize_t memtrace_read(struct file *filp, char __user *ubuf,
        return simple_read_from_buffer(ubuf, count, ppos, ent->mem, ent->size);
 }
 
+static int memtrace_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+       struct memtrace_entry *ent = filp->private_data;
+
+       if (ent->size < vma->vm_end - vma->vm_start)
+               return -EINVAL;
+
+       if (vma->vm_pgoff << PAGE_SHIFT >= ent->size)
+               return -EINVAL;
+
+       vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+       return remap_pfn_range(vma, vma->vm_start, PHYS_PFN(ent->start) + vma->vm_pgoff,
+                              vma->vm_end - vma->vm_start, vma->vm_page_prot);
+}
+
 static const struct file_operations memtrace_fops = {
        .llseek = default_llseek,
        .read   = memtrace_read,
        .open   = simple_open,
+       .mmap   = memtrace_mmap,
 };
 
 #define FLUSH_CHUNK_SIZE SZ_1G
@@ -187,7 +203,7 @@ static int memtrace_init_debugfs(void)
                dir = debugfs_create_dir(ent->name, memtrace_debugfs_dir);
 
                ent->dir = dir;
-               debugfs_create_file("trace", 0400, dir, ent, &memtrace_fops);
+               debugfs_create_file_unsafe("trace", 0600, dir, ent, &memtrace_fops);
                debugfs_create_x64("start", 0400, dir, &ent->start);
                debugfs_create_x64("size", 0400, dir, &ent->size);
        }