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From:   Haiyang Zhang <haiyangz@microsoft.com>
To:     Shradha Gupta <shradhagupta@linux.microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>
CC:     Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        KY Srinivasan <kys@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        Long Li <longli@microsoft.com>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: RE: [PATCH] hv_netvsc: support a new host capability
 AllowRscDisabledStatus
Thread-Topic: [PATCH] hv_netvsc: support a new host capability
 AllowRscDisabledStatus
Thread-Index: AQHZqnBMGWxSndAt1U6NS9TBDf5Ag6+huQmQ
Date:   Thu, 29 Jun 2023 12:44:26 +0000
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References: <1688032719-22847-1-git-send-email-shradhagupta@linux.microsoft.com>
In-Reply-To: <1688032719-22847-1-git-send-email-shradhagupta@linux.microsoft.com>
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> -----Original Message-----
> From: Shradha Gupta <shradhagupta@linux.microsoft.com>
> Sent: Thursday, June 29, 2023 5:59 AM
> To: linux-kernel@vger.kernel.org; linux-hyperv@vger.kernel.org;
> netdev@vger.kernel.org
> Cc: Shradha Gupta <shradhagupta@linux.microsoft.com>; Eric Dumazet
> <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>; Paolo Abeni
> <pabeni@redhat.com>; KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> <haiyangz@microsoft.com>; Wei Liu <wei.liu@kernel.org>; Dexuan Cui
> <decui@microsoft.com>; Long Li <longli@microsoft.com>; Michael Kelley
> (LINUX) <mikelley@microsoft.com>; David S. Miller <davem@davemloft.net>
> Subject: [PATCH] hv_netvsc: support a new host capability
> AllowRscDisabledStatus
>=20
> A future Azure host update has the potential to change RSC behavior
> in the VMs. To avoid this invisble change, Vswitch will check the
> netvsc version of a VM before sending its RSC capabilities, and will
> always indicate that the host performs RSC if the VM doesn't have an
> updated netvsc driver regardless of the actual host RSC capabilities.
> Netvsc now advertises a new capability: AllowRscDisabledStatus
> The host will check for this capability before sending RSC status,
> and if a VM does not have this capability it will send RSC enabled
> status regardless of host RSC settings
>=20
> Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
> ---
>  drivers/net/hyperv/hyperv_net.h | 3 +++
>  drivers/net/hyperv/netvsc.c     | 8 ++++++++
>  2 files changed, 11 insertions(+)
>=20
> diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_=
net.h
> index dd5919ec408b..218e0f31dd66 100644
> --- a/drivers/net/hyperv/hyperv_net.h
> +++ b/drivers/net/hyperv/hyperv_net.h
> @@ -572,6 +572,9 @@ struct nvsp_2_vsc_capability {
>  			u64 teaming:1;
>  			u64 vsubnetid:1;
>  			u64 rsc:1;
> +			u64 timestamp:1;
> +			u64 reliablecorrelationid:1;
> +			u64 allowrscdisabledstatus:1;
>  		};
>  	};
>  } __packed;
> diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
> index da737d959e81..2eb1e85ba940 100644
> --- a/drivers/net/hyperv/netvsc.c
> +++ b/drivers/net/hyperv/netvsc.c
> @@ -619,6 +619,14 @@ static int negotiate_nvsp_ver(struct hv_device
> *device,
>  	init_packet->msg.v2_msg.send_ndis_config.mtu =3D ndev->mtu +
> ETH_HLEN;
>  	init_packet->msg.v2_msg.send_ndis_config.capability.ieee8021q =3D 1;
>=20
> +	/* Don't need a version check while setting this bit because if we
> +	 * have a New VM on an old host, the VM will set the bit but the host
> +	 * won't check it. If we have an old VM on a new host, the host will
> +	 * check the bit, see its zero, and it'll know the VM has an
> +	 * older NetVsc
> +	 */
> +	init_packet-
> >msg.v2_msg.send_ndis_config.capability.allowrscdisabledstatus =3D 1;

Have you tested on the new host to verify: Before this patch, the host show=
s
RSC status on, and after this patch the host shows it's off?

Thanks,
- Haiyang