[PATCH 2/2] vhost-scsi: reject invalid 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.

Use a module parameter callback to reject out-of-range updates when the
parameter is written. This keeps the visible parameter value consistent
with the effective queue limit.

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

Invalid values now fail with -EINVAL at write/load time instead of being
accepted and silently adjusted later when the device is opened.

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
 drivers/vhost/scsi.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 0c0634eea144..c138c29ce3dd 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -210,7 +210,20 @@ 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)
+{
+	return param_set_uint_minmax(val, kp, 1, VHOST_SCSI_MAX_IO_VQ);
+}
+
+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 {
@@ -2273,22 +2286,14 @@ 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 += VHOST_SCSI_VQ_IO;
+	nvqs = vhost_scsi_max_io_vqs + VHOST_SCSI_VQ_IO;
 
 	vs->old_inflight = kmalloc_objs(*vs->old_inflight, nvqs,
 					GFP_KERNEL | __GFP_ZERO);
-- 
2.43.5