linux-kernel - Re: [PATCH RFC 3/4] xen/pvhvm: Unmap all PIRQs on startup and shutdown

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Date:	Mon, 28 Jul 2014 14:43:10 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>,
	<xen-devel@...ts.xenproject.org>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Andrew Jones <drjones@...hat.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 3/4] xen/pvhvm: Unmap all PIRQs on startup and shutdown

On 15/07/14 14:40, Vitaly Kuznetsov wrote:
> When kexec is being run PIRQs from Qemu-emulated devices are still
> mapped to old event channels and new kernel has no information about
> that. Trying to map them twice results in the following in Xen's dmesg:
> 
>  (XEN) irq.c:2278: dom7: pirq 24 or emuirq 8 already mapped
>  (XEN) irq.c:2278: dom7: pirq 24 or emuirq 12 already mapped
>  (XEN) irq.c:2278: dom7: pirq 24 or emuirq 1 already mapped
>  ...
> 
>  and the following in new kernel's dmesg:
> 
>  [   92.286796] xen:events: Failed to obtain physical IRQ 4
> 
> The result is that the new kernel doesn't recieve IRQs for Qemu-emulated
> devices. Address the issue by unmapping all mapped PIRQs on kernel shutdown
> when kexec was requested and on every kernel startup. We need to do this
> twice to deal with the following issues:
> - startup-time unmapping is required to make kdump work;
> - shutdown-time unmapping is required to support kexec-ing non-fixed kernels;
> - shutdown-time unmapping is required to make Qemu-emulated NICs work after
>   kexec (event channel is being closed on shutdown but no PHYSDEVOP_unmap_pirq
>   is being performed).

I think this should be done only in one place -- just prior to exec'ing
the new kernel (including kdump kernels).

> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -768,6 +768,7 @@ void xen_kexec_shutdown(void)
>  #ifdef CONFIG_KEXEC
>  	if (!kexec_in_progress)
>  		return;
> +	xen_unmap_all_pirqs();
>  #endif
>  }
>  
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index c919d3d..7701c7f 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -1643,6 +1643,80 @@ void xen_callback_vector(void) {}
>  static bool fifo_events = true;
>  module_param(fifo_events, bool, 0);
>  
> +void xen_unmap_all_pirqs(void)
> +{
> +	int pirq, rc, gsi, irq, evtchn;
> +	struct physdev_unmap_pirq unmap_irq;
> +	struct irq_info *info;
> +	struct evtchn_close close;
> +
> +	mutex_lock(&irq_mapping_update_lock);
> +
> +	list_for_each_entry(info, &xen_irq_list_head, list) {
> +		if (info->type != IRQT_PIRQ)
> +			continue;

I think you need to do this by querying Xen state rather than relying on
potentially bad guest state.  Particularly since you may crash while
holding irq_mapping_update_lock.

EVTCHNOP_status gets you the info you need I think.

David
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