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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 v11 3/3] vhost: Add configuration controls for vhost worker's mode Message-ID: <20250612022053-mutt-send-email-mst@kernel.org> References: <20250609073430.442159-1-lulu@redhat.com> <20250609073430.442159-4-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: <20250609073430.442159-4-lulu@redhat.com> On Mon, Jun 09, 2025 at 03:33:09PM +0800, Cindy Lu wrote: > This patch introduces functionality to control the vhost worker mode: > > - Add two new IOCTLs: > * VHOST_SET_FORK_FROM_OWNER: Allows userspace to select between > task mode (fork_owner=1) and kthread mode (fork_owner=0) > * VHOST_GET_FORK_FROM_OWNER: Retrieves the current thread mode > setting > > - Expose module parameter 'fork_from_owner_default' to allow system > administrators to configure the default mode for vhost workers > > - Add KConfig option CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL to > control the availability of these IOCTLs and parameter, allowing > distributions to disable them if not needed > > - The VHOST_NEW_WORKER functionality requires fork_owner to be set > to true, with validation added to ensure proper configuration > > Signed-off-by: Cindy Lu getting there. yet something to improve. > --- > drivers/vhost/Kconfig | 17 +++++++++++++++ > drivers/vhost/vhost.c | 44 ++++++++++++++++++++++++++++++++++++++ > include/uapi/linux/vhost.h | 25 ++++++++++++++++++++++ > 3 files changed, 86 insertions(+) > > diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig > index 020d4fbb947c..49e1d9dc92b7 100644 > --- a/drivers/vhost/Kconfig > +++ b/drivers/vhost/Kconfig > @@ -96,3 +96,20 @@ config VHOST_CROSS_ENDIAN_LEGACY > If unsure, say "N". > > endif > + > +config CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL > + bool "Enable CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL" > + default n > + help > + This option enables two IOCTLs: VHOST_SET_FORK_FROM_OWNER and > + VHOST_GET_FORK_FROM_OWNER. These allow userspace applications > + to modify the vhost worker mode for vhost devices. > + > + Also expose module parameter 'fork_from_owner_default' to allow users > + to configure the default mode for vhost workers. > + > + By default, `CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL` is set to `n`, > + which disables the IOCTLs and parameter. > + When enabled (y), users can change the worker thread mode as needed. > + > + If unsure, say "N". > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index 37d3ed8be822..903d9c3f6784 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -43,6 +43,11 @@ module_param(max_iotlb_entries, int, 0444); > MODULE_PARM_DESC(max_iotlb_entries, > "Maximum number of iotlb entries. (default: 2048)"); > static bool fork_from_owner_default = true; Add empty lines around ifdef to make it clear what code do they delimit. > +#ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL > +module_param(fork_from_owner_default, bool, 0444); > +MODULE_PARM_DESC(fork_from_owner_default, > + "Set task mode as the default(default: Y)"); > +#endif > > enum { > VHOST_MEMORY_F_LOG = 0x1, > @@ -1019,6 +1024,13 @@ 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 fork_owner must be true. > + */ > + if (!dev->fork_owner) > + return -EFAULT; An empty line here would make the code clearer. > ret = vhost_new_worker(dev, &state); > if (!ret && copy_to_user(argp, &state, sizeof(state))) > ret = -EFAULT; > @@ -1136,6 +1148,7 @@ void vhost_dev_reset_owner(struct vhost_dev *dev, struct vhost_iotlb *umem) > > vhost_dev_cleanup(dev); > > + dev->fork_owner = fork_from_owner_default; > dev->umem = umem; > /* We don't need VQ locks below since vhost_dev_cleanup makes sure > * VQs aren't running. > @@ -2289,6 +2302,37 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp) > goto done; > } > > +#ifdef CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL > + u8 fork_owner; Do not declare variables in the middle of a scope please. This one is not needed in this scope, so just move it down to within if (yes you will repeat the declaration twice then). > + > + if (ioctl == VHOST_SET_FORK_FROM_OWNER) { > + /*fork_owner can only be modified before owner is set*/ bad comment style. > + if (vhost_dev_has_owner(d)) { > + r = -EBUSY; > + goto done; > + } > + if (copy_from_user(&fork_owner, argp, sizeof(u8))) { get_user is a better fit for this. In particular, typesafe. > + r = -EFAULT; > + goto done; > + } > + if (fork_owner > 1) { so 0 and 1 are the only legal values? maybe add an enum or defines in the header then. > + r = -EINVAL; > + goto done; > + } > + d->fork_owner = (bool)fork_owner; !!fork_owner is shorter and idiomatic. > + r = 0; > + goto done; > + } > + if (ioctl == VHOST_GET_FORK_FROM_OWNER) { > + fork_owner = d->fork_owner; > + if (copy_to_user(argp, &fork_owner, sizeof(u8))) { put_user > + r = -EFAULT; > + goto done; > + } > + 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..e51d6a347607 100644 > --- a/include/uapi/linux/vhost.h > +++ b/include/uapi/linux/vhost.h > @@ -235,4 +235,29 @@ > */ > #define VHOST_VDPA_GET_VRING_SIZE _IOWR(VHOST_VIRTIO, 0x82, \ > struct vhost_vring_state) > + > +/** > + * VHOST_SET_FORK_FROM_OWNER - Set the fork_owner flag for the vhost device, > + * This ioctl must called before VHOST_SET_OWNER. > + * Only available when CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL=y > + * > + * @param fork_owner: An 8-bit value that determines the vhost thread mode > + * > + * When fork_owner is set to 1(default value): > + * - Vhost will create vhost worker as tasks forked from the owner, > + * inheriting all of the owner's attributes. > + * > + * When fork_owner is set to 0: > + * - Vhost will create vhost workers as kernel threads. > + */ > +#define VHOST_SET_FORK_FROM_OWNER _IOW(VHOST_VIRTIO, 0x83, __u8) > + > +/** > + * VHOST_GET_FORK_OWNER - Get the current fork_owner flag for the vhost device. > + * Only available when CONFIG_VHOST_ENABLE_FORK_OWNER_CONTROL=y > + * > + * @return: An 8-bit value indicating the current thread mode. > + */ > +#define VHOST_GET_FORK_FROM_OWNER _IOR(VHOST_VIRTIO, 0x84, __u8) > + > #endif > -- > 2.45.0