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Date: Fri, 5 May 2023 17:52:40 -0700 (PDT)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Rahul Singh <rahul.singh@....com>
cc: xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
Juergen Gross <jgross@...e.com>,
Stefano Stabellini <sstabellini@...nel.org>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
Samuel Holland <samuel@...lland.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Marc Zyngier <maz@...nel.org>,
Jane Malalane <jane.malalane@...rix.com>,
David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [PATCH] xen/evtchn: Introduce new IOCTL to bind static evtchn
On Fri, 28 Apr 2023, Rahul Singh wrote:
> Xen 4.17 supports the creation of static evtchns. To allow user space
> application to bind static evtchns introduce new ioctl
> "IOCTL_EVTCHN_BIND_STATIC". Existing IOCTL doing more than binding
> that’s why we need to introduce the new IOCTL to only bind the static
> event channels.
>
> Also, static evtchns to be available for use during the lifetime of the
> guest. When the application exits, __unbind_from_irq() end up
> being called from release() fop because of that static evtchns are
> getting closed. To avoid closing the static event channel, add the new
> bool variable "is_static" in "struct irq_info" to mark the event channel
> static when creating the event channel to avoid closing the static
> evtchn.
>
> Signed-off-by: Rahul Singh <rahul.singh@....com>
I think the patch is OK but evtchn_bind_to_user on the error path calls
EVTCHNOP_close. Could that be a problem for static evtchns? I wonder if
we need to skip that EVTCHNOP_close call too.
err:
/* bind failed, should close the port now */
close.port = port;
if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
BUG();
del_evtchn(u, evtchn);
> ---
> drivers/xen/events/events_base.c | 7 +++++--
> drivers/xen/evtchn.c | 22 +++++++++++++++++-----
> include/uapi/xen/evtchn.h | 9 +++++++++
> include/xen/events.h | 2 +-
> 4 files changed, 32 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index c7715f8bd452..31f2d3634ad5 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -112,6 +112,7 @@ struct irq_info {
> unsigned int irq_epoch; /* If eoi_cpu valid: irq_epoch of event */
> u64 eoi_time; /* Time in jiffies when to EOI. */
> raw_spinlock_t lock;
> + u8 is_static; /* Is event channel static */
>
> union {
> unsigned short virq;
> @@ -982,7 +983,8 @@ static void __unbind_from_irq(unsigned int irq)
> unsigned int cpu = cpu_from_irq(irq);
> struct xenbus_device *dev;
>
> - xen_evtchn_close(evtchn);
> + if (!info->is_static)
> + xen_evtchn_close(evtchn);
>
> switch (type_from_irq(irq)) {
> case IRQT_VIRQ:
> @@ -1574,7 +1576,7 @@ int xen_set_irq_priority(unsigned irq, unsigned priority)
> }
> EXPORT_SYMBOL_GPL(xen_set_irq_priority);
>
> -int evtchn_make_refcounted(evtchn_port_t evtchn)
> +int evtchn_make_refcounted(evtchn_port_t evtchn, bool is_static)
> {
> int irq = get_evtchn_to_irq(evtchn);
> struct irq_info *info;
> @@ -1590,6 +1592,7 @@ int evtchn_make_refcounted(evtchn_port_t evtchn)
> WARN_ON(info->refcnt != -1);
>
> info->refcnt = 1;
> + info->is_static = is_static;
>
> return 0;
> }
> diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
> index c99415a70051..47681d4c696b 100644
> --- a/drivers/xen/evtchn.c
> +++ b/drivers/xen/evtchn.c
> @@ -366,7 +366,8 @@ static int evtchn_resize_ring(struct per_user_data *u)
> return 0;
> }
>
> -static int evtchn_bind_to_user(struct per_user_data *u, evtchn_port_t port)
> +static int evtchn_bind_to_user(struct per_user_data *u, evtchn_port_t port,
> + bool is_static)
> {
> struct user_evtchn *evtchn;
> struct evtchn_close close;
> @@ -402,7 +403,7 @@ static int evtchn_bind_to_user(struct per_user_data *u, evtchn_port_t port)
> if (rc < 0)
> goto err;
>
> - rc = evtchn_make_refcounted(port);
> + rc = evtchn_make_refcounted(port, is_static);
> return rc;
>
> err:
> @@ -456,7 +457,7 @@ static long evtchn_ioctl(struct file *file,
> if (rc != 0)
> break;
>
> - rc = evtchn_bind_to_user(u, bind_virq.port);
> + rc = evtchn_bind_to_user(u, bind_virq.port, false);
> if (rc == 0)
> rc = bind_virq.port;
> break;
> @@ -482,7 +483,7 @@ static long evtchn_ioctl(struct file *file,
> if (rc != 0)
> break;
>
> - rc = evtchn_bind_to_user(u, bind_interdomain.local_port);
> + rc = evtchn_bind_to_user(u, bind_interdomain.local_port, false);
> if (rc == 0)
> rc = bind_interdomain.local_port;
> break;
> @@ -507,7 +508,7 @@ static long evtchn_ioctl(struct file *file,
> if (rc != 0)
> break;
>
> - rc = evtchn_bind_to_user(u, alloc_unbound.port);
> + rc = evtchn_bind_to_user(u, alloc_unbound.port, false);
> if (rc == 0)
> rc = alloc_unbound.port;
> break;
> @@ -536,6 +537,17 @@ static long evtchn_ioctl(struct file *file,
> break;
> }
>
> + case IOCTL_EVTCHN_BIND_STATIC: {
> + struct ioctl_evtchn_bind bind;
> +
> + rc = -EFAULT;
> + if (copy_from_user(&bind, uarg, sizeof(bind)))
> + break;
> +
> + rc = evtchn_bind_to_user(u, bind.port, true);
> + break;
> + }
> +
> case IOCTL_EVTCHN_NOTIFY: {
> struct ioctl_evtchn_notify notify;
> struct user_evtchn *evtchn;
> diff --git a/include/uapi/xen/evtchn.h b/include/uapi/xen/evtchn.h
> index 7fbf732f168f..aef2b75f3413 100644
> --- a/include/uapi/xen/evtchn.h
> +++ b/include/uapi/xen/evtchn.h
> @@ -101,4 +101,13 @@ struct ioctl_evtchn_restrict_domid {
> domid_t domid;
> };
>
> +/*
> + * Bind statically allocated @port.
> + */
> +#define IOCTL_EVTCHN_BIND_STATIC \
> + _IOC(_IOC_NONE, 'E', 7, sizeof(struct ioctl_evtchn_bind))
> +struct ioctl_evtchn_bind {
> + unsigned int port;
> +};
> +
> #endif /* __LINUX_PUBLIC_EVTCHN_H__ */
> diff --git a/include/xen/events.h b/include/xen/events.h
> index 44c2855c76d1..962f0bbc7ce1 100644
> --- a/include/xen/events.h
> +++ b/include/xen/events.h
> @@ -69,7 +69,7 @@ int xen_set_irq_priority(unsigned irq, unsigned priority);
> /*
> * Allow extra references to event channels exposed to userspace by evtchn
> */
> -int evtchn_make_refcounted(evtchn_port_t evtchn);
> +int evtchn_make_refcounted(evtchn_port_t evtchn, bool is_static);
> int evtchn_get(evtchn_port_t evtchn);
> void evtchn_put(evtchn_port_t evtchn);
>
> --
> 2.25.1
>
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