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Subject: Re: [PATCH v3 2/8] xen/events: don't unmask an event channel when an
 eoi is pending
To:     Ross Lagerwall <ross.lagerwall@citrix.com>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org
Cc:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        stable@vger.kernel.org, Julien Grall <julien@xen.org>
References: <20210219154030.10892-1-jgross@suse.com>
 <20210219154030.10892-3-jgross@suse.com>
 <d368a948-17d6-4e64-110e-bede3158f49f@citrix.com>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Message-ID: <134540c1-40ac-3607-6ca0-3dcd5f83a013@suse.com>
Date:   Sat, 6 Mar 2021 17:18:25 +0100
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From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
To: Ross Lagerwall <ross.lagerwall@citrix.com>,
 xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
 Stefano Stabellini <sstabellini@kernel.org>, stable@vger.kernel.org,
 Julien Grall <julien@xen.org>
Message-ID: <134540c1-40ac-3607-6ca0-3dcd5f83a013@suse.com>
Subject: Re: [PATCH v3 2/8] xen/events: don't unmask an event channel when an
 eoi is pending
References: <20210219154030.10892-1-jgross@suse.com>
 <20210219154030.10892-3-jgross@suse.com>
 <d368a948-17d6-4e64-110e-bede3158f49f@citrix.com>
In-Reply-To: <d368a948-17d6-4e64-110e-bede3158f49f@citrix.com>

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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 chann=
el
>> 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@vger.kernel.org
>> Fixes: 54c9de89895e0a36047 ("xen/events: add a new late EOI evtchn fra=
mework")
>> Reported-by: Julien Grall <julien@xen.org>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>=20
> 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 wi=
ll
> end up in a state with some event channels pending and masked in dom0
> which breaks networking in the guest.
>=20
> The issue seems to have been introduced with this patch, though at firs=
t
> glance it appears correct. I haven't yet looked into why it is happenin=
g.
> Have you seen anything like this with this patch?

I have found the issue. lateeoi_mask_ack_dynirq() must not set the "eoi"
mask reason flag, as this callback will be called when the handler will
not be called later, so there will never be a call of xen_irq_lateeoi()
to unmask the event channel again.

Juergen


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