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From:   Michael Kelley <mikelley@microsoft.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "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>
Subject: RE: [PATCH 2/2] Drivers: hv: vmbus: Resolve more races involving
 init_vp_index()
Thread-Topic: [PATCH 2/2] Drivers: hv: vmbus: Resolve more races involving
 init_vp_index()
Thread-Index: AQHWMF1AqQ3jESdKyEKGe2bznL+fZai0cBRw
Date:   Fri, 22 May 2020 18:41:13 +0000
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 <20200522171901.204127-3-parri.andrea@gmail.com>
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From: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
>=20
> init_vp_index() uses the (per-node) hv_numa_map[] masks to record the
> CPUs allocated for channel interrupts at a given time, and distribute
> the performance-critical channels across the available CPUs: in part.,
> the mask of "candidate" target CPUs in a given NUMA node, for a newly
> offered channel, is determined by XOR-ing the node's CPU mask and the
> node's hv_numa_map.  This operation/mechanism assumes that no offline
> CPUs is set in the hv_numa_map mask, an assumption that does not hold
> since such mask is currently not updated when a channel is removed or
> assigned to a different CPU.
>=20
> To address the issues described above, this adds hooks in the channel
> removal path (hv_process_channel_removal()) and in target_cpu_store()
> in order to clear, resp. to update, the hv_numa_map[] masks as needed.
> This also adds a (missed) update of the masks in init_vp_index() (cf.,
> e.g., the memory-allocation failure path in this function).
>=20
> Like in the case of init_vp_index(), such hooks require to determine
> if the given channel is performance critical.  init_vp_index() does
> this by parsing the channel's offer, it can not rely on the device
> data structure (device_obj) to retrieve such information because the
> device data structure has not been allocated/linked with the channel
> by the time that init_vp_index() executes.  A similar situation may
> hold in hv_is_alloced_cpu() (defined below); the adopted approach is
> to "cache" the device type of the channel, as computed by parsing the
> channel's offer, in the channel structure itself.
>=20
> Fixes: 7527810573436f ("Drivers: hv: vmbus: Introduce the
> CHANNELMSG_MODIFYCHANNEL message type")
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> ---
>  drivers/hv/channel_mgmt.c | 22 +++++++++++++-----
>  drivers/hv/hyperv_vmbus.h | 48 +++++++++++++++++++++++++++++++++++++++
>  drivers/hv/vmbus_drv.c    | 19 +++++++++++-----
>  include/linux/hyperv.h    |  7 ++++++
>  4 files changed, 84 insertions(+), 12 deletions(-)

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