[PATCH] hv_netvsc: support a new host capability AllowRscDisabledStatus

[Shradha Gupta]

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

Signed-off-by: Shradha Gupta <shradhagupta@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/hyperv/hyperv_net.h | 3 +++
 drivers/net/hyperv/netvsc.c     | 8 ++++++++
 2 files changed, 11 insertions(+)

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 = ndev->mtu + ETH_HLEN;
 	init_packet->msg.v2_msg.send_ndis_config.capability.ieee8021q = 1;
 
+	/* 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 = 1;
+
 	if (nvsp_ver >= NVSP_PROTOCOL_VERSION_5) {
 		if (hv_is_isolation_supported())
 			netdev_info(ndev, "SR-IOV not advertised by guests on the host supporting isolation\n");
-- 
2.34.1