[PATCH v8 8/8] vhost: Add a KConfig knob to enable IOCTL VHOST_FORK_FROM_OWNER

Cindy Lu
2025-03-28T10:05:42Z

Introduce a new config knob `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL`,
to control the availability of the `VHOST_FORK_FROM_OWNER` ioctl.
When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is set to n, the ioctl
is disabled, and any attempt to use it will result in failure.

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
drivers/vhost/Kconfig | 15 +++++++++++++++
drivers/vhost/vhost.c | 3 +++
2 files changed, 18 insertions(+)

diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index b455d9ab6f3d..e5b9dcbf31b6 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -95,3 +95,18 @@ config VHOST_CROSS_ENDIAN_LEGACY
If unsure, say "N".

endif
+
+config VHOST_ENABLE_FORK_OWNER_IOCTL
+ bool "Enable IOCTL VHOST_FORK_FROM_OWNER"
+ default n
+ help
+ This option enables the IOCTL VHOST_FORK_FROM_OWNER, which allows
+ userspace applications to modify the thread mode for vhost devices.
+
+ By default, `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL` is set to `n`,
+ meaning the ioctl is disabled and any operation using this ioctl
+ will fail.
+ When the configuration is enabled (y), the ioctl becomes
+ available, allowing users to set the mode if needed.
+
+ If unsure, say "N".
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index fb0c7fb43f78..568e43cb54a9 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2294,6 +2294,8 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
r = vhost_dev_set_owner(d);
goto done;
}
+
+#ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL
if (ioctl == VHOST_FORK_FROM_OWNER) {
u8 inherit_owner;
/*inherit_owner can only be modified before owner is set*/
@@ -2313,6 +2315,7 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
r = 0;
goto done;
}
+#endif
/* You must be the owner to do anything else */
r = vhost_dev_check_owner(d);
if (r)
--
2.45.0