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From:   Michael Kelley <mikelley@microsoft.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        vkuznets <vkuznets@redhat.com>
Subject: RE: [PATCH 01/11] Drivers: hv: vmbus: Always handle the VMBus
 messages on CPU0
Thread-Topic: [PATCH 01/11] Drivers: hv: vmbus: Always handle the VMBus
 messages on CPU0
Thread-Index: AQHWC6imTi8OATtO/kWMIYPL49c6q6hyoGmg
Date:   Fri, 10 Apr 2020 17:18:22 +0000
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From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Sent: Sunday, April=
 5, 2020 5:15 PM
>=20
> A Linux guest have to pick a "connect CPU" to communicate with the
> Hyper-V host.  This CPU can not be taken offline because Hyper-V does
> not provide a way to change that CPU assignment.
>=20
> Current code sets the connect CPU to whatever CPU ends up running the
> function vmbus_negotiate_version(), and this will generate problems if
> that CPU is taken offine.
>=20
> Establish CPU0 as the connect CPU, and add logics to prevents the
> connect CPU from being taken offline.   We could pick some other CPU,
> and we could pick that "other CPU" dynamically if there was a reason to
> do so at some point in the future.  But for now, #defining the connect
> CPU to 0 is the most straightforward and least complex solution.
>=20
> While on this, add inline comments explaining "why" offer and rescind
> messages should not be handled by a same serialized work queue.
>=20
> Suggested-by: Dexuan Cui <decui@microsoft.com>
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  drivers/hv/connection.c   | 20 +-------------------
>  drivers/hv/hv.c           |  7 +++++++
>  drivers/hv/hyperv_vmbus.h | 11 ++++++-----
>  drivers/hv/vmbus_drv.c    | 20 +++++++++++++++++---
>  4 files changed, 31 insertions(+), 27 deletions(-)

Reviewed-by: Michael Kelley <mikelley@microsoft.com>