Add a new UAPI to support setting the vhost device to
use task mode. The user space application needs to use
VHOST_SET_ENFORCE_TASK to set the mode. This setting must
be set before VHOST_SET_OWNER is set.

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 drivers/vhost/vhost.c      | 16 +++++++++++++++-
 include/uapi/linux/vhost.h |  2 ++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index bf1e971cb06f..8ed6b3a947a9 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2340,14 +2340,28 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 {
 	struct eventfd_ctx *ctx;
 	u64 p;
-	long r;
+	long r = 0;
 	int i, fd;
+	bool enforce_task;
 
 	/* If you are not the owner, you can become one */
 	if (ioctl == VHOST_SET_OWNER) {
 		r = vhost_dev_set_owner(d);
 		goto done;
 	}
+	if (ioctl == VHOST_SET_ENFORCE_TASK) {
+		/* Is there an owner already? */
+		if (vhost_dev_has_owner(d)) {
+			r = -EBUSY;
+			goto done;
+		}
+		if (copy_from_user(&kthread, argp, sizeof(enforce_task))) {
+			r = -EFAULT;
+			goto done;
+		}
+		use_kthread = enforce_task;
+		goto done;
+	}
 
 	/* You must be the owner to do anything else */
 	r = vhost_dev_check_owner(d);
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index b95dd84eef2d..9853d62d2d34 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -235,4 +235,6 @@
  */
 #define VHOST_VDPA_GET_VRING_SIZE	_IOWR(VHOST_VIRTIO, 0x82,	\
 					      struct vhost_vring_state)
+
+#define VHOST_SET_ENFORCE_TASK _IOW(VHOST_VIRTIO, 0x83, bool)
 #endif
-- 
2.45.0

Hi Cindy,

kernel test robot noticed the following build errors:

[auto build test ERROR on mst-vhost/linux-next]
[also build test ERROR on linus/master v6.11-rc7 next-20240911]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Cindy-Lu/vhost-Add-a-new-module_param-for-enable-kthread/20240909-093852
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git linux-next
patch link:    https://lore.kernel.org/r/20240909013531.1243525-8-lulu%40redhat.com
patch subject: [PATCH v1 7/7] vhost: Add new UAPI to support change to task mode
config: arc-randconfig-001-20240911 (https://download.01.org/0day-ci/archive/20240911/202409112119.BJdqPVTC-lkp@intel.com/config)
compiler: arc-elf-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240911/202409112119.BJdqPVTC-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409112119.BJdqPVTC-lkp@intel.com/

All errors (new ones prefixed by >>):

   drivers/vhost/vhost.c: In function 'vhost_worker_queue':
   drivers/vhost/vhost.c:273:13: error: 'use_kthread' undeclared (first use in this function)
     273 |         if (use_kthread) {
         |             ^~~~~~~~~~~
   drivers/vhost/vhost.c:273:13: note: each undeclared identifier is reported only once for each function it appears in
   drivers/vhost/vhost.c: In function 'vhost_workers_free':
   drivers/vhost/vhost.c:805:13: error: 'use_kthread' undeclared (first use in this function)
     805 |         if (use_kthread)
         |             ^~~~~~~~~~~
   drivers/vhost/vhost.c: In function 'vhost_worker_create':
   drivers/vhost/vhost.c:986:13: error: 'use_kthread' undeclared (first use in this function)
     986 |         if (use_kthread)
         |             ^~~~~~~~~~~
   drivers/vhost/vhost.c: In function 'vhost_free_worker':
   drivers/vhost/vhost.c:1030:13: error: 'use_kthread' undeclared (first use in this function)
    1030 |         if (use_kthread)
         |             ^~~~~~~~~~~
   drivers/vhost/vhost.c: In function 'vhost_dev_ioctl':
>> drivers/vhost/vhost.c:2358:37: error: 'kthread' undeclared (first use in this function); did you mean 'kthreadd'?
    2358 |                 if (copy_from_user(&kthread, argp, sizeof(enforce_task))) {
         |                                     ^~~~~~~
         |                                     kthreadd
   drivers/vhost/vhost.c:2362:17: error: 'use_kthread' undeclared (first use in this function)
    2362 |                 use_kthread = enforce_task;
         |                 ^~~~~~~~~~~
   drivers/vhost/vhost.c: In function 'vhost_worker_create':
   drivers/vhost/vhost.c:990:1: warning: control reaches end of non-void function [-Wreturn-type]
     990 | }
         | ^


vim +2358 drivers/vhost/vhost.c

  2337	
  2338	/* Caller must have device mutex */
  2339	long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
  2340	{
  2341		struct eventfd_ctx *ctx;
  2342		u64 p;
  2343		long r = 0;
  2344		int i, fd;
  2345		bool enforce_task;
  2346	
  2347		/* If you are not the owner, you can become one */
  2348		if (ioctl == VHOST_SET_OWNER) {
  2349			r = vhost_dev_set_owner(d);
  2350			goto done;
  2351		}
  2352		if (ioctl == VHOST_SET_ENFORCE_TASK) {
  2353			/* Is there an owner already? */
  2354			if (vhost_dev_has_owner(d)) {
  2355				r = -EBUSY;
  2356				goto done;
  2357			}
> 2358			if (copy_from_user(&kthread, argp, sizeof(enforce_task))) {
  2359				r = -EFAULT;
  2360				goto done;
  2361			}
  2362			use_kthread = enforce_task;
  2363			goto done;
  2364		}
  2365	
  2366		/* You must be the owner to do anything else */
  2367		r = vhost_dev_check_owner(d);
  2368		if (r)
  2369			goto done;
  2370	
  2371		switch (ioctl) {
  2372		case VHOST_SET_MEM_TABLE:
  2373			r = vhost_set_memory(d, argp);
  2374			break;
  2375		case VHOST_SET_LOG_BASE:
  2376			if (copy_from_user(&p, argp, sizeof p)) {
  2377				r = -EFAULT;
  2378				break;
  2379			}
  2380			if ((u64)(unsigned long)p != p) {
  2381				r = -EFAULT;
  2382				break;
  2383			}
  2384			for (i = 0; i < d->nvqs; ++i) {
  2385				struct vhost_virtqueue *vq;
  2386				void __user *base = (void __user *)(unsigned long)p;
  2387				vq = d->vqs[i];
  2388				mutex_lock(&vq->mutex);
  2389				/* If ring is inactive, will check when it's enabled. */
  2390				if (vq->private_data && !vq_log_access_ok(vq, base))
  2391					r = -EFAULT;
  2392				else
  2393					vq->log_base = base;
  2394				mutex_unlock(&vq->mutex);
  2395			}
  2396			break;
  2397		case VHOST_SET_LOG_FD:
  2398			r = get_user(fd, (int __user *)argp);
  2399			if (r < 0)
  2400				break;
  2401			ctx = fd == VHOST_FILE_UNBIND ? NULL : eventfd_ctx_fdget(fd);
  2402			if (IS_ERR(ctx)) {
  2403				r = PTR_ERR(ctx);
  2404				break;
  2405			}
  2406			swap(ctx, d->log_ctx);
  2407			for (i = 0; i < d->nvqs; ++i) {
  2408				mutex_lock(&d->vqs[i]->mutex);
  2409				d->vqs[i]->log_ctx = d->log_ctx;
  2410				mutex_unlock(&d->vqs[i]->mutex);
  2411			}
  2412			if (ctx)
  2413				eventfd_ctx_put(ctx);
  2414			break;
  2415		default:
  2416			r = -ENOIOCTLCMD;
  2417			break;
  2418		}
  2419	done:
  2420		return r;
  2421	}
  2422	EXPORT_SYMBOL_GPL(vhost_dev_ioctl);
  2423	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki