Re: OvmfXen and PVH

[Stefan Kadow <xen@xxxxxxxx>]

Am Mittwoch, 5. Januar 2022, 18:19:19 CET schrieb Anthony PERARD:
> On Tue, Jan 04, 2022 at 03:37:12PM +0100, Stefan Kadow wrote:
> > Hello,
> > I read in an old post from 2019 that the specific OVMF target platform
> > OvmfXen can boot in a PVH type domU. And in another old post I read that a
> > new console type was built for use with this PVH domUs.
> > I was hoping that I could use it to boot Linux PVH DomUs with EFIstub
> > kernels or systemd-boot, but I can't get it to work.
>
> Thanks for testing this! Unfortunately, there's still a little bit of
> work on the project. OvmfXen doesn't know how to shutdown when run as
> PVH yet, and this is checked at boot time so it doesn't even try to 
> boot
> the operating system.
>
> > I use a simple pvh-domu.cfg:
> > type = "pvh"
> > kernel = "/usr/lib/xen/boot/ovmf.bin"
> > disk = [...]
> > vif = [...]
> > ...
> >
> > In the verbose output of xl toolstack (xl -vvv create -c pvh-domu.cfg) I
> > can see that the domU is destroyed right after creation. The same domU
> > configuration works as HVM domU and as PVH domU with pygrub bootloader.
> I don't know why the guest would be destroyed, is there some 
> information
> before that? Maybe `xl` didn't recognized "ovmf.bin" as a PVH "kernel"?
>
> In the issue I've mention above, I think OvmfXen would just run an
> infinite loop, so the guess wouldn't be destroyed.
Obviously i misinterpreted the log outputs, because after i installed 
your patch, the system behaved as you predicted and the log outputs were 
the same.
> > Is there any way to get this to work with Xen 4.16.0?
>
> By hacking OVMF and rebuilding it. Otherwise not really. Sorry.
>
> For you or anyone looking at testing OVMF on PVH, the hack is going to
> be:
>
> diff --git a/OvmfPkg/Library/ResetSystemLib/DxeResetShutdown.c
> b/OvmfPkg/Library/ResetSystemLib/DxeResetShutdown.c ---
> a/OvmfPkg/Library/ResetSystemLib/DxeResetShutdown.c
> +++ b/OvmfPkg/Library/ResetSystemLib/DxeResetShutdown.c
> @@ -35,9 +35,7 @@ DxeResetInit (
>        mAcpiPmBaseAddress = ICH9_PMBASE_VALUE;
>        break;
>      default:
> -      ASSERT (FALSE);
> -      CpuDeadLoop ();
> -      return EFI_UNSUPPORTED;
> +      break;
>    }
>
>    return EFI_SUCCESS;
>
>
> With that, the guest should boot, but shutdown isn't going to work so
> one will have to destroy the guest after trying to shutdown.
>
> There's also a build option to have OVMF logging somewhere when run as
> PVH, "-D DEBUG_ON_HYPERVISOR_CONSOLE", which would log to the host
> serial console. But that might only work with a debug build of xen and
> one would probably need a serial port.
Thanks for this patch!
This is a very nice way to boot a pvh type guest, it boots very fast and 
allows configuring the boot manager inside the guest. I hope that this 
feature will be included in a future release as soon as possible.
I will try to create a debug build of xen to help test this feature in 
the future xen release candidate.
--
THX