Re: [Xen-devel] Guidance for PVHv2 usage?

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, May 29, 2017 at 08:58:04AM -0700, PGNet Dev wrote:
> Starting with
> 
>       Xen Changes For Linux 4.11: Lands PVHv2 Guest Support
>       
> https://www.phoronix.com/scan.php?page=news_item&px=Linux-4.11-Xen-Changes
> 
>       [GIT PULL] xen: features and fixes for 4.11-rc0
>       http://lkml.iu.edu/hypermail/linux/kernel/1702.2/03209.html
> 
> IIUC, Xen 4.9 + kernel-default > v4.11 should now fully support PVHv2?

For DomUs yes, for Dom0 not yet.

> I'm running Xen 4.9.0 host on kernel 4.11.3
> 
>       dmesg | egrep -i "linux version|xen version"
>               [    0.000000] Linux version 4.11.3-2.g7262353-default 
> (geeko@buildhost) (gcc version 7.1.1 20170517 [gcc-7-branch revision 248152] 
> (SUSE Linux) ) #1 SMP PREEMPT Thu May 25 17:55:04 UTC 2017 (7262353)
>               [    0.000000] Xen version: 4.9.0_07-503 (preserve-AD)
> 
> , both installed from pkgs built for an Opensuse Leap 42.2 env.
> 
> The docs @
> 
>       https://xenbits.xen.org/docs/unstable/misc/hvmlite.html
>       
> https://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html#Support-for-Paravirtualisation-of-HVM-Guests
> 
> are not clear on usage.
> 
> This
> 
>       https://xenbits.xen.org/docs/unstable/misc/pvh.html
> 
> suggests that for
> 
>       PVH 
>               ...
>               ELFNOTE(Xen, XEN_ELFNOTE_LOADER,         .asciz, "generic")
>               ...

Forget about this document, I should have removed it as part of the
PVHv1 code removal. In any case, those where PVHv1 internal details,
that are to no use to the end user.

> the .cfg spec'n should be
> 
>       builder='generic'
> 
> but, there's no mention of which value for specific PVHv2 usage.
> 
> Poking around, I've found discussion that PVH may be eventually retired, and 
> replaced with PVHv2, with same usage.
> 
> Is that the case already?  Or is there a transition state in effect, where 
> both are available?

Almost, Xen is still currently transitioning from PVHv1 to PVHv2.
PVHv1 is not available anymore, and PVHv2 is still experimental (and
not finished in the Dom0 case).

> Atm, I do have a 'converted' HVM guest booting into _some- form of PVH for 
> testing.
> 
> My current setup -- cobbled together from old PVH notes and some older posts, 
> contains, in Grub
> 
>       GRUB_CMDLINE_XEN="dom0=hvm dom0_mem=4G,max:4G dom0_max_vcpus=4 ..."
>                         ^^^^^^^^

I guess this is in the Dom0 grub config file? In any case, please
hold off before trying Dom0, it's still not in a working state.

> and in Guest.cfg
> 
>       builder = 'linux'
>       kernel = '/usr/lib/grub2/x86_64-xen/grub.xen'
>       xen_platform_pci = 1
>       device_model_version = 'qemu-xen'
>       ...

I'm not really sure what this guest is, PV I assume?

builder = 'linux' is not a valid option [0]. Also grub.xen (which I
imagine is pvgrub) is not going to work for PVHv2, you will have to
direct boot into the kernel you wish to use. For example a suitable
config file for PVHv2 would be:

builder='hvm'
device_model_version='none'

kernel='/path/to/kernel'
ramdisk='/path/to/initrd'

Note that this is a temporary interface, this is subject to change.

> 
> With that^, the guest *IS* up & , as far as I've tested, functional.
> 
> At current host & guest loglevels, I've not yet seen any errors  -- I'm just 
> not yet clear whether it's successfully, or completely & correctly, PVHv2 ...
> 
> Bottom line -- 
> 
> What *IS* the config/usage for PVHv2?  (Any current docs available?)

Since the interface is not yet finished, no, there are no current docs
available, sorry.

Roger.

[0] http://xenbits.xen.org/docs/unstable/man/xl.cfg.5.html#Selecting-Guest-Type

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