[PATCH v2 2/2] vhost-scsi: clamp max_io_vqs module parameter

[Dongli Zhang <dongli.zhang@oracle.com>]

max_io_vqs is currently validated only when a vhost-scsi device is opened.
This allows sysfs to show values larger than the driver will actually use,
e.g. writing 2048 succeeds even though vhost_scsi_open() later clamps it to
VHOST_SCSI_MAX_IO_VQ. This makes the sysfs value differ from the value that
will actually be used.

hv# echo 2048 > /sys/module/vhost_scsi/parameters/max_io_vqs

hv# cat /sys/module/vhost_scsi/parameters/max_io_vqs
2048

[  315.630495] Invalid max_io_vqs of 2048. Using 1024.

Keep accepting out-of-range values for compatibility, but clamp them in the
module parameter setter and store the effective value. This preserves the
existing behavior that invalid values do not make module loading or sysfs
writes fail. It also makes reads report the value that will actually be
used.

With the parameter value kept in range, remove the duplicate validation
from vhost_scsi_open().

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
v1->v2:
  - Access vhost_scsi_max_io_vqs with READ_ONCE().
  - Clamp out-of-range max_io_vqs values instead of rejecting them.

 drivers/vhost/scsi.c | 43 +++++++++++++++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 10 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 0c0634eea144..fb262cf9a34d 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -210,7 +210,37 @@ static const int vhost_scsi_bits[] = {
 #define VHOST_SCSI_MAX_EVENT	128
 
 static unsigned vhost_scsi_max_io_vqs = 128;
-module_param_named(max_io_vqs, vhost_scsi_max_io_vqs, uint, 0644);
+
+static int vhost_scsi_set_max_io_vqs(const char *val,
+				     const struct kernel_param *kp)
+{
+	unsigned int max_io_vqs;
+	int ret;
+
+	ret = kstrtouint(val, 0, &max_io_vqs);
+	if (ret)
+		return ret;
+
+	if (max_io_vqs > VHOST_SCSI_MAX_IO_VQ) {
+		pr_err("Invalid max_io_vqs of %u. Using %u.\n",
+		       max_io_vqs, VHOST_SCSI_MAX_IO_VQ);
+		max_io_vqs = VHOST_SCSI_MAX_IO_VQ;
+	} else if (!max_io_vqs) {
+		pr_err("Invalid max_io_vqs of 0. Using 1.\n");
+		max_io_vqs = 1;
+	}
+
+	WRITE_ONCE(vhost_scsi_max_io_vqs, max_io_vqs);
+	return 0;
+}
+
+static const struct kernel_param_ops vhost_scsi_max_io_vqs_op = {
+	.set = vhost_scsi_set_max_io_vqs,
+	.get = param_get_uint,
+};
+
+module_param_cb(max_io_vqs, &vhost_scsi_max_io_vqs_op,
+		&vhost_scsi_max_io_vqs, 0644);
 MODULE_PARM_DESC(max_io_vqs, "Set the max number of IO virtqueues a vhost scsi device can support. The default is 128. The max is 1024.");
 
 struct vhost_scsi_virtqueue {
@@ -2273,21 +2303,14 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
 	struct vhost_scsi_virtqueue *svq;
 	struct vhost_scsi *vs;
 	struct vhost_virtqueue **vqs;
-	int r = -ENOMEM, i, nvqs = vhost_scsi_max_io_vqs;
+	int r = -ENOMEM, i, nvqs;
 
 	vs = kvzalloc_obj(*vs);
 	if (!vs)
 		goto err_vs;
 	vs->inline_sg_cnt = vhost_scsi_inline_sg_cnt;
 
-	if (nvqs > VHOST_SCSI_MAX_IO_VQ) {
-		pr_err("Invalid max_io_vqs of %d. Using %d.\n", nvqs,
-		       VHOST_SCSI_MAX_IO_VQ);
-		nvqs = VHOST_SCSI_MAX_IO_VQ;
-	} else if (nvqs == 0) {
-		pr_err("Invalid max_io_vqs of %d. Using 1.\n", nvqs);
-		nvqs = 1;
-	}
+	nvqs = READ_ONCE(vhost_scsi_max_io_vqs);
 	nvqs += VHOST_SCSI_VQ_IO;
 
 	vs->old_inflight = kmalloc_objs(*vs->old_inflight, nvqs,
-- 
2.43.5