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From:   Michael Kelley <mikelley@microsoft.com>
To:     vkuznets <vkuznets@redhat.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>
CC:     Andres Beltran <lkmlabelt@gmail.com>,
        "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>,
        Dexuan Cui <decui@microsoft.com>, Wei Liu <wei.liu@kernel.org>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] hv_utils: Set the maximum packet size for VSS driver to
 the length of the receive buffer
Thread-Topic: [PATCH] hv_utils: Set the maximum packet size for VSS driver to
 the length of the receive buffer
Thread-Index: AQHXmbaUNIgJapnVhU6HmoUvQ6T8zquEi4Bg
Date:   Wed, 25 Aug 2021 18:33:10 +0000
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References: <20210825133857.847866-1-vkuznets@redhat.com>
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From: Vitaly Kuznetsov <vkuznets@redhat.com> Sent: Wednesday, August 25, 20=
21 6:39 AM
>=20
> Commit adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V ou=
t
> of the ring buffer") introduced a notion of maximum packet size and for
> KVM and FCOPY drivers set it to the length of the receive buffer. VSS
> driver wasn't updated, this means that the maximum packet size is now
> VMBUS_DEFAULT_MAX_PKT_SIZE (4k). Apparently, this is not enough. I'm
> observing a packet of 6304 bytes which is being truncated to 4096. When
> VSS driver tries to read next packet from ring buffer it starts from the
> wrong offset and receives garbage.
>=20
> Set the maximum packet size to 'HV_HYP_PAGE_SIZE * 2' in VSS driver. This
> matches the length of the receive buffer and is in line with other utils
> drivers.
>=20
> Fixes: adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V ou=
t of the ring buffer")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  drivers/hv/hv_snapshot.c | 1 +
>  1 file changed, 1 insertion(+)
>=20
> diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
> index 2267bd4c3472..6018b9d1b1fb 100644
> --- a/drivers/hv/hv_snapshot.c
> +++ b/drivers/hv/hv_snapshot.c
> @@ -375,6 +375,7 @@ hv_vss_init(struct hv_util_service *srv)
>  	}
>  	recv_buffer =3D srv->recv_buffer;
>  	vss_transaction.recv_channel =3D srv->channel;
> +	vss_transaction.recv_channel->max_pkt_size =3D HV_HYP_PAGE_SIZE * 2;
>=20
>  	/*
>  	 * When this driver loads, the user level daemon that
> --
> 2.31.1

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