Re: [PATCH] hv_netvsc: support a new host capability AllowRscDisabledStatus

[Shradha Gupta]

On Thu, Jun 29, 2023 at 12:44:26PM +0000, Haiyang Zhang wrote:
> 
> 
> > -----Original Message-----
> > From: Shradha Gupta <shradhagupta@xxxxxxxxxxxxxxxxxxx>
> > Sent: Thursday, June 29, 2023 5:59 AM
> > To: linux-kernel@xxxxxxxxxxxxxxx; linux-hyperv@xxxxxxxxxxxxxxx;
> > netdev@xxxxxxxxxxxxxxx
> > Cc: Shradha Gupta <shradhagupta@xxxxxxxxxxxxxxxxxxx>; Eric Dumazet
> > <edumazet@xxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni
> > <pabeni@xxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang
> > <haiyangz@xxxxxxxxxxxxx>; Wei Liu <wei.liu@xxxxxxxxxx>; Dexuan Cui
> > <decui@xxxxxxxxxxxxx>; Long Li <longli@xxxxxxxxxxxxx>; Michael Kelley
> > (LINUX) <mikelley@xxxxxxxxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>
> > Subject: [PATCH] hv_netvsc: support a new host capability
> > AllowRscDisabledStatus
> > 
> > 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;
> 
> Have you tested on the new host to verify: Before this patch, the host shows
> RSC status on, and after this patch the host shows it's off?
I have completed the patch sanilty tests. We are working on an upgraded host setup
to test the rsc specific changes, will update with results soon.
> 
> Thanks,
> - Haiyang