[RFC,09/11] KVM: arm64: Add raw interface for hyp tracefs

Commit Message

Vincent Donnefort Aug. 5, 2024, 5:32 p.m. UTC

The raw interface enables userspace tools such as trace-cmd to directly
read the ring-buffer without any decoding by the kernel.

Signed-off-by: Vincent Donnefort <[e-mail]>

Patch

diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index b4de7650cd8f..36c120aeabc0 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -649,6 +649,86 @@  static const struct file_operations hyp_trace_pipe_fops = {
 	.llseek         = no_llseek,
 };
 
+static ssize_t
+hyp_trace_raw_read(struct file *file, char __user *ubuf,
+		   size_t cnt, loff_t *ppos)
+{
+	struct ht_iterator *iter = (struct ht_iterator *)file->private_data;
+	size_t size;
+	int ret;
+
+	if (iter->copy_leftover)
+		goto read;
+
+again:
+	ret = ring_buffer_read_page(iter->trace_buffer,
+				    (struct buffer_data_read_page *)iter->spare,
+				    cnt, iter->cpu, 0);
+	if (ret < 0) {
+		if (!ring_buffer_empty_cpu(iter->trace_buffer, iter->cpu))
+			return 0;
+
+		ret = ring_buffer_wait(iter->trace_buffer, iter->cpu, 0, NULL,
+				       NULL);
+		if (ret < 0)
+			return ret;
+
+		goto again;
+	}
+
+	iter->copy_leftover = 0;
+
+read:
+	size = PAGE_SIZE - iter->copy_leftover;
+	if (size > cnt)
+		size = cnt;
+
+	ret = copy_to_user(ubuf, iter->spare + PAGE_SIZE - size, size);
+	if (ret == size)
+		return -EFAULT;
+
+	size -= ret;
+	*ppos += size;
+	iter->copy_leftover = ret;
+
+	return size;
+}
+
+static int hyp_trace_raw_open(struct inode *inode, struct file *file)
+{
+	int ret = hyp_trace_pipe_open(inode, file);
+	struct ht_iterator *iter;
+
+	if (ret)
+		return ret;
+
+	iter = file->private_data;
+	iter->spare = ring_buffer_alloc_read_page(iter->trace_buffer, iter->cpu);
+	if (IS_ERR(iter->spare)) {
+		ret = PTR_ERR(iter->spare);
+		iter->spare = NULL;
+		return ret;
+	}
+
+	return 0;
+}
+
+static int hyp_trace_raw_release(struct inode *inode, struct file *file)
+{
+	struct ht_iterator *iter = file->private_data;
+
+	ring_buffer_free_read_page(iter->trace_buffer, iter->cpu, iter->spare);
+
+	return hyp_trace_pipe_release(inode, file);
+}
+
+static const struct file_operations hyp_trace_raw_fops = {
+	.open           = hyp_trace_raw_open,
+	.read           = hyp_trace_raw_read,
+	.release        = hyp_trace_raw_release,
+	.llseek         = no_llseek,
+};
+
 static int hyp_trace_open(struct inode *inode, struct file *file)
 {
 	return file->f_mode & FMODE_WRITE ? hyp_tracing_teardown() : 0;
@@ -723,6 +803,8 @@  int hyp_trace_init_tracefs(void)
 		}
 		tracefs_create_file("trace_pipe", TRACEFS_MODE_READ, per_cpu_dir,
 				    (void *)cpu, &hyp_trace_pipe_fops);
+		tracefs_create_file("trace_pipe_raw", TRACEFS_MODE_READ, per_cpu_dir,
+				    (void *)cpu, &hyp_trace_pipe_fops);
 	}
 
 	return 0;