[PATCH 1/3] powernv/memtrace: Allow mmaping trace buffers

[Jordan Niethe]

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 at gmail.com>
---
 arch/powerpc/platforms/powernv/memtrace.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/memtrace.c b/arch/powerpc/platforms/powernv/memtrace.c
index 5fc9408bb0b3..8a1df39305e9 100644
--- a/arch/powerpc/platforms/powernv/memtrace.c
+++ b/arch/powerpc/platforms/powernv/memtrace.c
@@ -45,10 +45,26 @@ static ssize_t memtrace_read(struct file *filp, char __user *ubuf,
 	return simple_read_from_buffer(ubuf, count, ppos, ent->mem, ent->size);
 }
 
+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,
 };
 
 static void memtrace_clear_range(unsigned long start_pfn,
@@ -158,7 +174,7 @@ 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);
 	}
-- 
2.25.1