linux-kernel - Re: [PATCH v3 2/8] xen/events: don't unmask an event channel when an eoi is pending

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Date:   Fri, 5 Mar 2021 11:53:25 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Ross Lagerwall <ross.lagerwall@...rix.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 v3 2/8] xen/events: don't unmask an event channel when an
 eoi is pending

On 23.02.21 10:26, Ross Lagerwall wrote:
> On 2021-02-19 15:40, 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 three different flags for each event channel
>> to be able to distinguish "normal" masking/unmasking from eoi related
>> masking/unmasking and temporary masking. The event channel should only
>> be able to generate an interrupt if all 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>
> 
> I tested this patch series backported to a 4.19 kernel and found that
> when doing a reboot loop of Windows with PV drivers, occasionally it will
> end up in a state with some event channels pending and masked in dom0
> which breaks networking in the guest.
> 
> The issue seems to have been introduced with this patch, though at first
> glance it appears correct. I haven't yet looked into why it is happening.
> Have you seen anything like this with this patch?

Sorry it took so long, but now I was able to look into this issue.

I have managed to reproduce it with a pv Linux guest. I'm now adding
some debug code to understand what is happening there.


Juergen

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