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SubjectRe: [PATCH v5 3/3] vfio/pci: make use of irq_update_devid and optimize irq ops
On Fri, 30 Aug 2019 16:42:06 +0800
Ben Luo <luoben@linux.alibaba.com> wrote:

> When userspace (e.g. qemu) triggers a switch between KVM
> irqfd and userspace eventfd, only dev_id of irqaction
> (i.e. the "trigger" in this patch's context) will be
> changed, but a free-then-request-irq action is taken in
> current code. And, irq affinity setting in VM will also
> trigger a free-then-request-irq action, which actually
> changes nothing, but only need to bounce the irqbypass
> registraion in case that posted-interrupt is in use.
>
> This patch makes use of irq_update_devid() and optimize
> both cases above, which reduces the risk of losing interrupt
> and also cuts some overhead.
>
> Signed-off-by: Ben Luo <luoben@linux.alibaba.com>
> ---
> drivers/vfio/pci/vfio_pci_intrs.c | 124 ++++++++++++++++++++++++++------------
> 1 file changed, 87 insertions(+), 37 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> index 3fa3f72..d3a93d7 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -284,70 +284,120 @@ static int vfio_msi_enable(struct vfio_pci_device *vdev, int nvec, bool msix)
> static int vfio_msi_set_vector_signal(struct vfio_pci_device *vdev,
> int vector, int fd, bool msix)
> {
> + struct eventfd_ctx *trigger = NULL;
> struct pci_dev *pdev = vdev->pdev;
> - struct eventfd_ctx *trigger;
> int irq, ret;
>
> if (vector < 0 || vector >= vdev->num_ctx)
> return -EINVAL;
>
> + if (fd >= 0) {
> + trigger = eventfd_ctx_fdget(fd);
> + if (IS_ERR(trigger)) {
> + /* oops, going to disable this interrupt */
> + dev_info(&pdev->dev,
> + "get ctx error on bad fd: %d for vector:%d\n",
> + fd, vector);

I think a user could trigger this maliciously as a denial of service by
simply providing a bogus file descriptor. The user is informed of the
error by the return value, why do we need to spam the logs?

> + }
> + }
> +
> irq = pci_irq_vector(pdev, vector);
>
> + /*
> + * 'trigger' is NULL or invalid, disable the interrupt
> + * 'trigger' is same as before, only bounce the bypass registration
> + * 'trigger' is a new invalid one, update it to irqaction and other

s/invalid/valid/

> + * data structures referencing to the old one; fallback to disable
> + * the interrupt on error
> + */
> if (vdev->ctx[vector].trigger) {
> - free_irq(irq, vdev->ctx[vector].trigger);
> + /*
> + * even if the trigger is unchanged we need to bounce the
> + * interrupt bypass connection to allow affinity changes in
> + * the guest to be realized.
> + */
> irq_bypass_unregister_producer(&vdev->ctx[vector].producer);
> - kfree(vdev->ctx[vector].name);
> - eventfd_ctx_put(vdev->ctx[vector].trigger);
> - vdev->ctx[vector].trigger = NULL;
> +
> + if (vdev->ctx[vector].trigger == trigger) {
> + /* avoid duplicated referencing to the same trigger */
> + eventfd_ctx_put(trigger);
> +
> + } else if (trigger && !IS_ERR(trigger)) {
> + ret = irq_update_devid(irq,
> + vdev->ctx[vector].trigger, trigger);
> + if (unlikely(ret)) {
> + dev_info(&pdev->dev,
> + "update devid of %d (token %p) failed: %d\n",
> + irq, vdev->ctx[vector].trigger, ret);
> + eventfd_ctx_put(trigger);
> + free_irq(irq, vdev->ctx[vector].trigger);
> + kfree(vdev->ctx[vector].name);
> + eventfd_ctx_put(vdev->ctx[vector].trigger);
> + vdev->ctx[vector].trigger = NULL;
> + return ret;
> + }
> + eventfd_ctx_put(vdev->ctx[vector].trigger);
> + vdev->ctx[vector].producer.token = trigger;
> + vdev->ctx[vector].trigger = trigger;
> +
> + } else {
> + free_irq(irq, vdev->ctx[vector].trigger);
> + kfree(vdev->ctx[vector].name);
> + eventfd_ctx_put(vdev->ctx[vector].trigger);
> + vdev->ctx[vector].trigger = NULL;
> + }
> }
>
> if (fd < 0)
> return 0;
> + else if (IS_ERR(trigger))
> + return PTR_ERR(trigger);
>
> - vdev->ctx[vector].name = kasprintf(GFP_KERNEL, "vfio-msi%s[%d](%s)",
> - msix ? "x" : "", vector,
> - pci_name(pdev));
> - if (!vdev->ctx[vector].name)
> - return -ENOMEM;
> + if (!vdev->ctx[vector].trigger) {
> + vdev->ctx[vector].name = kasprintf(GFP_KERNEL,
> + "vfio-msi%s[%d](%s)",
> + msix ? "x" : "", vector,
> + pci_name(pdev));
> + if (!vdev->ctx[vector].name) {
> + eventfd_ctx_put(trigger);
> + return -ENOMEM;
> + }
>
> - trigger = eventfd_ctx_fdget(fd);
> - if (IS_ERR(trigger)) {
> - kfree(vdev->ctx[vector].name);
> - return PTR_ERR(trigger);
> - }
> + /*
> + * The MSIx vector table resides in device memory which may be
> + * cleared via backdoor resets. We don't allow direct access to
> + * the vector table so even if a userspace driver attempts to
> + * save/restore around such a reset it would be unsuccessful.
> + * To avoid this, restore the cached value of the message prior
> + * to enabling.
> + */
> + if (msix) {
> + struct msi_msg msg;
>
> - /*
> - * The MSIx vector table resides in device memory which may be cleared
> - * via backdoor resets. We don't allow direct access to the vector
> - * table so even if a userspace driver attempts to save/restore around
> - * such a reset it would be unsuccessful. To avoid this, restore the
> - * cached value of the message prior to enabling.
> - */
> - if (msix) {
> - struct msi_msg msg;
> + get_cached_msi_msg(irq, &msg);
> + pci_write_msi_msg(irq, &msg);
> + }
>
> - get_cached_msi_msg(irq, &msg);
> - pci_write_msi_msg(irq, &msg);
> - }
> + ret = request_irq(irq, vfio_msihandler, 0,
> + vdev->ctx[vector].name, trigger);
> + if (ret) {
> + kfree(vdev->ctx[vector].name);
> + eventfd_ctx_put(trigger);
> + return ret;
> + }
>
> - ret = request_irq(irq, vfio_msihandler, 0,
> - vdev->ctx[vector].name, trigger);
> - if (ret) {
> - kfree(vdev->ctx[vector].name);
> - eventfd_ctx_put(trigger);
> - return ret;
> + vdev->ctx[vector].producer.token = trigger;
> + vdev->ctx[vector].producer.irq = irq;
> + vdev->ctx[vector].trigger = trigger;
> }
>
> - vdev->ctx[vector].producer.token = trigger;
> - vdev->ctx[vector].producer.irq = irq;
> + /* setup bypass connection and make irte updated */
> ret = irq_bypass_register_producer(&vdev->ctx[vector].producer);
> if (unlikely(ret))
> dev_info(&pdev->dev,
> "irq bypass producer (token %p) registration fails: %d\n",
> vdev->ctx[vector].producer.token, ret);
>
> - vdev->ctx[vector].trigger = trigger;
> -
> return 0;
> }
>

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