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Re: [Xen-devel] [PATCH 2/4] x86/IRQ: bail early from irq_guest_eoi_timer_fn() when nothing is in flight
- To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 5 Jun 2019 18:15:33 +0100
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- Cc: Wei Liu <wei.liu2@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 05 Jun 2019 17:15:47 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 08/05/2019 13:46, Jan Beulich wrote:
> There's no point entering the loop in the function in this case. Instead
> there still being something in flight _after_ the loop would be an
> actual problem: No timer would be running anymore for issuing the EOI
> eventually, and hence this IRQ (and possibly lower priority ones) would
> be blocked, perhaps indefinitely.
>
> Issue a warning instead and prefer breaking some (presumably
> misbehaving) guest over stalling perhaps the entire system.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> --- a/xen/arch/x86/irq.c
> +++ b/xen/arch/x86/irq.c
> @@ -1115,7 +1115,7 @@ static void irq_guest_eoi_timer_fn(void
>
> action = (irq_guest_action_t *)desc->action;
>
> - if ( timer_is_active(&action->eoi_timer) )
> + if ( !action->in_flight || timer_is_active(&action->eoi_timer) )
> goto out;
>
> if ( action->ack_type != ACKTYPE_NONE )
> @@ -1130,8 +1130,10 @@ static void irq_guest_eoi_timer_fn(void
> }
> }
>
> - if ( action->in_flight != 0 )
> - goto out;
> + if ( action->in_flight )
> + printk(XENLOG_G_WARNING
> + "IRQ%d: %d handlers still in flight at forced EOI\n",
> + desc->irq, action->in_flight);
AFACIT, this condition can be triggered by a buggy/malicious guest, by
it simply ignoring or masking the line interrupt at the vIO-APIC.
The message would be far more useful if it identified the domain in
question, which looks like it can be obtained from the middle of the loop.
~Andrew
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