linux-kernel - Re: [PATCH 2/7] xen/events: don't unmask an event channel when an eoi is pending

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Message-ID: <bdf20a87-5b4d-529e-7028-cea3eeef769b@citrix.com>
Date:   Mon, 8 Feb 2021 10:15:31 +0000
From:   Ross Lagerwall <ross.lagerwall@...rix.com>
To:     Juergen Gross <jgross@...e.com>, <xen-devel@...ts.xenproject.org>,
        <linux-kernel@...r.kernel.org>
CC:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        <stable@...r.kernel.org>, Julien Grall <julien@....org>
Subject: Re: [PATCH 2/7] xen/events: don't unmask an event channel when an eoi
 is pending

On 2021-02-06 10:49, Juergen Gross wrote:
> An event channel should be kept masked when an eoi is pending for it.
> When being migrated to another cpu it might be unmasked, though.
> 
> In order to avoid this keep two different flags for each event channel
> to be able to distinguish "normal" masking/unmasking from eoi related
> masking/unmasking. The event channel should only be able to generate
> an interrupt if both flags are cleared.
> 
> Cc: stable@...r.kernel.org
> Fixes: 54c9de89895e0a36047 ("xen/events: add a new late EOI evtchn framework")
> Reported-by: Julien Grall <julien@....org>
> Signed-off-by: Juergen Gross <jgross@...e.com>
...> +static void lateeoi_ack_dynirq(struct irq_data *data)
> +{
> +	struct irq_info *info = info_for_irq(data->irq);
> +	evtchn_port_t evtchn = info ? info->evtchn : 0;
> +
> +	if (VALID_EVTCHN(evtchn)) {
> +		info->eoi_pending = true;
> +		mask_evtchn(evtchn);
> +	}
> +}

Doesn't this (and the one below) need a call to clear_evtchn() to
actually ack the pending event? Otherwise I can't see what clears
the pending bit.

I tested out this patch but processes using the userspace evtchn device did
not work very well without the clear_evtchn() call.

Ross

> +
> +static void lateeoi_mask_ack_dynirq(struct irq_data *data)
> +{
> +	struct irq_info *info = info_for_irq(data->irq);
> +	evtchn_port_t evtchn = info ? info->evtchn : 0;
> +
> +	if (VALID_EVTCHN(evtchn)) {
> +		info->masked = true;
> +		info->eoi_pending = true;
> +		mask_evtchn(evtchn);
> +	}
> +}
> +