Xen / EC2 network HVM device visibility

Xen / EC2 network HVM device visibility

[Andrew Stuart]

As far as I can tell, Xen HVM domu guests detect and use the RTL8139 network card thus its not a hard requirement to use the PVHVM drivers.

On EC2 however, am I right in understanding that although EC2 is using Xen HVM, the RTL8139 network device is not available and therefore to get networking it is a requirement for PVHVM drivers?

thanks

as

Re: Xen / EC2 network HVM device visibility

[Ian Campbell]

On Wed, 2015-09-30 at 15:25 +1000, Andrew Stuart wrote:

This is not a question about the development of the Xen hypervisor.
Therefore I've moved xen-devel to bcc and added xen-users to the cc. Please
try and use the correct list in the future.

> As far as I can tell, Xen HVM domu guests detect and use the RTL8139
> network card thus its not a hard requirement to use the PVHVM drivers.

Correct. Strictly speaking you can also configure other emulated nics (e.g.
e1000) rtl8139 is just the default. You can also configure just a PV NIC
without any emulated NIC at all.

> On EC2 however, am I right in understanding that although EC2 is using
> Xen HVM, the RTL8139 network device is not available and therefore to get
> networking it is a requirement for PVHVM drivers?

It's not clear from some web searches and it may not even be the same for
all HVM instance types.

The easiest way to tell would be to create whichever sort of instance you
are interested in and look at the logs + lspci etc.

Ian.

Re: Xen / EC2 network HVM device visibility

[Wei Liu]

On Wed, Sep 30, 2015 at 03:25:20PM +1000, Andrew Stuart wrote:
> As far as I can tell, Xen HVM domu guests detect and use the RTL8139
> network card thus its not a hard requirement to use the PVHVM drivers.
> 

That's because the default emulated nic in libxl is RTL8139. You can
specify others as well.  And yes, you're free to not use PVHVM drivers.

> On EC2 however, am I right in understanding that although EC2 is using
> Xen HVM, the RTL8139 network device is not available and therefore to
> get networking it is a requirement for PVHVM drivers?
> 

We can't answer this question because we don't run EC2 after all. You'd
better try to reach EC2 engineers for this question.

Wei.

> thanks
> 
> as _______________________________________________ Xen-devel mailing
> list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel

Re: Xen / EC2 network HVM device visibility

[Andrew Cooper]

On 30/09/15 06:25, Andrew Stuart wrote:
> As far as I can tell, Xen HVM domu guests detect and use the RTL8139 network card thus its not a hard requirement to use the PVHVM drivers.

The rtl8139 (or e1000e, depending on configuration) are provided to HVM
guests to cater to a Xen unaware configuration.

It is expected that any Xen aware operating system use xen-netfront instead.

>
> On EC2 however, am I right in understanding that although EC2 is using Xen HVM, the RTL8139 network device is not available and therefore to get networking it is a requirement for PVHVM drivers?

As part of booting and being Xen aware, there is a handover to disable
the emulated card, to avoid the VM having two network interfaces on the
same bridge with the same mac address.  If you instruct your VM to boot
without enabling any Xen PV drivers, you will likely still find an
emulated card visible.

~Andrew

Re: Xen / EC2 network HVM device visibility

[Paul Durrant]

> -----Original Message-----
> From: xen-devel-bounces@lists.xen.org [mailto:xen-devel-
> bounces@lists.xen.org] On Behalf Of Andrew Cooper
> Sent: 30 September 2015 10:11
> To: Andrew Stuart; xen-devel@lists.xen.org
> Subject: Re: [Xen-devel] Xen / EC2 network HVM device visibility
> 
> On 30/09/15 06:25, Andrew Stuart wrote:
> > As far as I can tell, Xen HVM domu guests detect and use the RTL8139
> network card thus its not a hard requirement to use the PVHVM drivers.
> 
> The rtl8139 (or e1000e, depending on configuration) are provided to HVM
> guests to cater to a Xen unaware configuration.
> 
> It is expected that any Xen aware operating system use xen-netfront
> instead.
> 
> >
> > On EC2 however, am I right in understanding that although EC2 is using Xen
> HVM, the RTL8139 network device is not available and therefore to get
> networking it is a requirement for PVHVM drivers?
> 
> As part of booting and being Xen aware, there is a handover to disable
> the emulated card, to avoid the VM having two network interfaces on the
> same bridge with the same mac address.  If you instruct your VM to boot
> without enabling any Xen PV drivers, you will likely still find an
> emulated card visible.
>

I believe AWS VMs are not configured with an emulated network so a PV frontend is required.

  Paul

 
> ~Andrew
> 
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