Re: [RFC PATCH v6 17/20] vfio: add local lock in virqfd instead of depending on VFIO PCI

Alex Williamson
2014-06-05T22:19:30Z

On Thu, 2014-06-05 at 19:03 +0200, Antonios Motakis wrote:
> Sharing the same spinlock with the VFIO bus driver is not necessary for
> the virqfd code, so remove that dependency.

I like the idea of consolidating this code, but I need more
justification for why the use of the lock here is independent of the bus
driver and why it's ok to move from a per-device lock to a global lock.
Thanks,

Alex

>
> Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
> ---
> drivers/vfio/pci/vfio_pci_intrs.c | 10 +++++-----
> drivers/vfio/virqfd.c | 24 +++++++++++++-----------
> include/linux/vfio.h | 3 +--
> 3 files changed, 19 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> index 3f909bb..e56c814 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -226,8 +226,8 @@ static int vfio_intx_set_signal(struct vfio_pci_device *vdev, int fd)
> static void vfio_intx_disable(struct vfio_pci_device *vdev)
> {
> vfio_intx_set_signal(vdev, -1);
> - virqfd_disable(vdev, &vdev->ctx[0].unmask);
> - virqfd_disable(vdev, &vdev->ctx[0].mask);
> + virqfd_disable(&vdev->ctx[0].unmask);
> + virqfd_disable(&vdev->ctx[0].mask);
> vdev->irq_type = VFIO_PCI_NUM_IRQS;
> vdev->num_ctx = 0;
> kfree(vdev->ctx);
> @@ -377,8 +377,8 @@ static void vfio_msi_disable(struct vfio_pci_device *vdev, bool msix)
> vfio_msi_set_block(vdev, 0, vdev->num_ctx, NULL, msix);
>
> for (i = 0; i < vdev->num_ctx; i++) {
> - virqfd_disable(vdev, &vdev->ctx[i].unmask);
> - virqfd_disable(vdev, &vdev->ctx[i].mask);
> + virqfd_disable(&vdev->ctx[i].unmask);
> + virqfd_disable(&vdev->ctx[i].mask);
> }
>
> if (msix) {
> @@ -415,7 +415,7 @@ static int vfio_pci_set_intx_unmask(struct vfio_pci_device *vdev,
> vfio_send_intx_eventfd, NULL,
> &vdev->ctx[0].unmask, fd);
>
> - virqfd_disable(vdev, &vdev->ctx[0].unmask);
> + virqfd_disable(&vdev->ctx[0].unmask);
> }
>
> return 0;
> diff --git a/drivers/vfio/virqfd.c b/drivers/vfio/virqfd.c
> index 9cf2842..4528450 100644
> --- a/drivers/vfio/virqfd.c
> +++ b/drivers/vfio/virqfd.c
> @@ -17,6 +17,7 @@
> #include "pci/vfio_pci_private.h"
>
> static struct workqueue_struct *vfio_irqfd_cleanup_wq;
> +static spinlock_t lock;
>
> int __init vfio_pci_virqfd_init(void)
> {
> @@ -25,6 +26,8 @@ int __init vfio_pci_virqfd_init(void)
> if (!vfio_irqfd_cleanup_wq)
> return -ENOMEM;
>
> + spin_lock_init(&lock);
> +
> return 0;
> }
>
> @@ -53,21 +56,21 @@ static int virqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
>
> if (flags & POLLHUP) {
> unsigned long flags;
> - spin_lock_irqsave(&virqfd->vdev->irqlock, flags);
> + spin_lock_irqsave(&lock, flags);
>
> /*
> * The eventfd is closing, if the virqfd has not yet been
> * queued for release, as determined by testing whether the
> - * vdev pointer to it is still valid, queue it now. As
> + * virqfd pointer to it is still valid, queue it now. As
> * with kvm irqfds, we know we won't race against the virqfd
> - * going away because we hold wqh->lock to get here.
> + * going away because we hold the lock to get here.
> */
> if (*(virqfd->pvirqfd) == virqfd) {
> *(virqfd->pvirqfd) = NULL;
> virqfd_deactivate(virqfd);
> }
>
> - spin_unlock_irqrestore(&virqfd->vdev->irqlock, flags);
> + spin_unlock_irqrestore(&lock, flags);
> }
>
> return 0;
> @@ -143,16 +146,16 @@ int virqfd_enable(struct vfio_pci_device *vdev,
> * we update the pointer to the virqfd under lock to avoid
> * pushing multiple jobs to release the same virqfd.
> */
> - spin_lock_irq(&vdev->irqlock);
> + spin_lock_irq(&lock);
>
> if (*pvirqfd) {
> - spin_unlock_irq(&vdev->irqlock);
> + spin_unlock_irq(&lock);
> ret = -EBUSY;
> goto err_busy;
> }
> *pvirqfd = virqfd;
>
> - spin_unlock_irq(&vdev->irqlock);
> + spin_unlock_irq(&lock);
>
> /*
> * Install our own custom wake-up handling so we are notified via
> @@ -189,19 +192,18 @@ err_fd:
> return ret;
> }
>
> -void virqfd_disable(struct vfio_pci_device *vdev,
> - struct virqfd **pvirqfd)
> +void virqfd_disable(struct virqfd **pvirqfd)
> {
> unsigned long flags;
>
> - spin_lock_irqsave(&vdev->irqlock, flags);
> + spin_lock_irqsave(&lock, flags);
>
> if (*pvirqfd) {
> virqfd_deactivate(*pvirqfd);
> *pvirqfd = NULL;
> }
>
> - spin_unlock_irqrestore(&vdev->irqlock, flags);
> + spin_unlock_irqrestore(&lock, flags);
>
> /*
> * Block until we know all outstanding shutdown jobs have completed.
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index 43968e8..44c9808 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -123,7 +123,6 @@ extern int virqfd_enable(struct vfio_pci_device *vdev,
> int (*handler)(struct vfio_pci_device *, void *),
> void (*thread)(struct vfio_pci_device *, void *),
> void *data, struct virqfd **pvirqfd, int fd);
> -extern void virqfd_disable(struct vfio_pci_device *vdev,
> - struct virqfd **pvirqfd);
> +extern void virqfd_disable(struct virqfd **pvirqfd);
>
> #endif /* VFIO_H */