linux-kernel - Re: [PATCH v2 3/3] xen/events: Update virq_to

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Message-ID: <b57adcd5-59ca-4f0c-b584-e32bb6bf76ca@suse.com>
Date: Wed, 27 Aug 2025 17:28:25 +0200
From: Jürgen Groß <jgross@...e.com>
To: Jason Andryuk <jason.andryuk@....com>,
 Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 Chris Wright <chrisw@...s-sol.org>,
 Jeremy Fitzhardinge <jeremy@...source.com>
Cc: stable@...r.kernel.org, xen-devel@...ts.xenproject.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] xen/events: Update virq_to_irq on migration

On 26.08.25 02:55, Jason Andryuk wrote:
> VIRQs come in 3 flavors, per-VPU, per-domain, and global, and the VIRQs
> are tracked in per-cpu virq_to_irq arrays.
> 
> Per-domain and global VIRQs must be bound on CPU 0, and
> bind_virq_to_irq() sets the per_cpu virq_to_irq at registration time
> Later, the interrupt can migrate, and info->cpu is updated.  When
> calling __unbind_from_irq(), the per-cpu virq_to_irq is cleared for a
> different cpu.  If bind_virq_to_irq() is called again with CPU 0, the
> stale irq is returned.  There won't be any irq_info for the irq, so
> things break.
> 
> Make xen_rebind_evtchn_to_cpu() update the per_cpu virq_to_irq mappings
> to keep them update to date with the current cpu.  This ensures the
> correct virq_to_irq is cleared in __unbind_from_irq().
> 
> Fixes: e46cdb66c8fc ("xen: event channels")
> Cc: stable@...r.kernel.org
> Signed-off-by: Jason Andryuk <jason.andryuk@....com>
> ---
> V2:
> Different approach changing virq_to_irq
> ---
>   drivers/xen/events/events_base.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index a85bc43f4344..4e9db7b92dde 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -1772,6 +1772,7 @@ static int xen_rebind_evtchn_to_cpu(struct irq_info *info, unsigned int tcpu)
>   {
>   	struct evtchn_bind_vcpu bind_vcpu;
>   	evtchn_port_t evtchn = info ? info->evtchn : 0;
> +	int old_cpu = info ? info->cpu : tcpu;

I'd prefer not to initialize old_cpu just here ...

>   
>   	if (!VALID_EVTCHN(evtchn))
>   		return -1;

... as here info is always valid, so you can just use "old_cpu = info->cpu;"
(probably just after the hypercall).

> @@ -1795,8 +1796,18 @@ static int xen_rebind_evtchn_to_cpu(struct irq_info *info, unsigned int tcpu)
>   	 * it, but don't do the xenlinux-level rebind in that case.
>   	 */
>   	if (HYPERVISOR_event_channel_op(EVTCHNOP_bind_vcpu, &bind_vcpu) >= 0)
> +	{

Kernel style, please.

>   		bind_evtchn_to_cpu(info, tcpu, false);
>   
> +		if (info->type == IRQT_VIRQ) {
> +			int virq = info->u.virq;
> +			int irq = per_cpu(virq_to_irq, old_cpu)[virq];
> +
> +			per_cpu(virq_to_irq, old_cpu)[virq] = -1;
> +			per_cpu(virq_to_irq, tcpu)[virq] = irq;
> +		}
> +	}
> +
>   	do_unmask(info, EVT_MASK_REASON_TEMPORARY);
>   
>   	return 0;


Juergen

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