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Tsirkin" To: Cindy Lu Cc: jasowang@redhat.com, michael.christie@oracle.com, sgarzare@redhat.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: Re: [PATCH RESEND v10 3/3] vhost: Add new UAPI to select kthread mode and KConfig to enable this IOCTL Message-ID: <20250601064429-mutt-send-email-mst@kernel.org> References: <20250531095800.160043-1-lulu@redhat.com> <20250531095800.160043-4-lulu@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250531095800.160043-4-lulu@redhat.com> On Sat, May 31, 2025 at 05:57:28PM +0800, Cindy Lu wrote: > This patch introduces a new UAPI that allows the vhost device to select > in kthread mode. Userspace applications can utilize IOCTL > VHOST_FORK_FROM_OWNER to select between task and kthread modes, which > must be invoked before IOCTL VHOST_SET_OWNER, as the worker will be > created during that call. > > The VHOST_NEW_WORKER requires the inherit_owner setting to be true, and > a check has been added to ensure proper configuration. > > Additionally, a new KConfig option, CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL, > is introduced to control the availability of the IOCTL > VHOST_FORK_FROM_OWNER. When CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL is set > to n, the IOCTL is disabled, and any attempt to use it will result in a > failure. > > Signed-off-by: Cindy Lu I propose renaming CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL to CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL and it should also control the presence of the module parameter and a get ioctl (more on which below). Otherwise we can get a situation where task mode is disabled and there is no way for userspace to override or check. > --- > drivers/vhost/Kconfig | 13 +++++++++++++ > drivers/vhost/vhost.c | 30 +++++++++++++++++++++++++++++- > include/uapi/linux/vhost.h | 16 ++++++++++++++++ > 3 files changed, 58 insertions(+), 1 deletion(-) > > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig > index 020d4fbb947c..300e474b60fd 100644 > --- a/drivers/vhost/Kconfig > +++ b/drivers/vhost/Kconfig > @@ -96,3 +96,16 @@ 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, allowing > + userspace applications to modify the thread mode for vhost devices. > + > + By default, `CONFIG_VHOST_ENABLE_FORK_OWNER_IOCTL` is set to `n`, > + which disables the IOCTL. When enabled (y), the IOCTL allows > + users to set the mode as needed. > + > + If unsure, say "N". > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 2d2909be1bb2..cfa60dc438f9 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -1022,6 +1022,13 @@ long vhost_worker_ioctl(struct vhost_dev *dev, unsigned int ioctl, > switch (ioctl) { > /* dev worker ioctls */ > case VHOST_NEW_WORKER: > + /* > + * vhost_tasks will account for worker threads under the parent's > + * NPROC value but kthreads do not. To avoid userspace overflowing > + * the system with worker threads inherit_owner must be true. > + */ > + if (!dev->inherit_owner) > + return -EFAULT; > ret = vhost_new_worker(dev, &state); > if (!ret && copy_to_user(argp, &state, sizeof(state))) > ret = -EFAULT; > @@ -1138,7 +1145,7 @@ void vhost_dev_reset_owner(struct vhost_dev *dev, struct vhost_iotlb *umem) > int i; > > vhost_dev_cleanup(dev); > - > + dev->inherit_owner = inherit_owner_default; > dev->umem = umem; > /* We don't need VQ locks below since vhost_dev_cleanup makes sure > * VQs aren't running. > @@ -2292,6 +2299,27 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp) > 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*/ > + if (vhost_dev_has_owner(d)) { > + r = -EBUSY; > + goto done; > + } > + if (copy_from_user(&inherit_owner, argp, sizeof(u8))) { > + r = -EFAULT; > + goto done; > + } > + if (inherit_owner > 1) { > + r = -EINVAL; > + goto done; > + } > + d->inherit_owner = (bool)inherit_owner; > + r = 0; > + goto done; > + } > +#endif > /* You must be the owner to do anything else */ > r = vhost_dev_check_owner(d); > if (r) > diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h > index d4b3e2ae1314..d2692c7ef450 100644 > --- a/include/uapi/linux/vhost.h > +++ b/include/uapi/linux/vhost.h > @@ -235,4 +235,20 @@ > */ > #define VHOST_VDPA_GET_VRING_SIZE _IOWR(VHOST_VIRTIO, 0x82, \ > struct vhost_vring_state) > + > +/** > + * VHOST_FORK_FROM_OWNER - Set the inherit_owner flag for the vhost device, > + * This ioctl must called before VHOST_SET_OWNER. > + * > + * @param inherit_owner: An 8-bit value that determines the vhost thread mode > + * > + * When inherit_owner is set to 1(default value): > + * - Vhost will create tasks similar to processes forked from the owner, > + * inheriting all of the owner's attributes. > + * > + * When inherit_owner is set to 0: > + * - Vhost will create tasks as kernel thread. > + */ > +#define VHOST_FORK_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, __u8) Given default now depends on the module parameter, we should have both GET and SET ioctls. All controlled by the kconfig knob. > + > #endif > -- > 2.45.0