Re: [RFC PATCH] pvh: Introduce SIF_HVM_GHCB for SEV-ES/SNP guests

[Anthony PERARD <anthony@xenproject.org>]

On Fri, Jan 09, 2026 at 12:37:30PM +0100, Roger Pau Monné wrote:
> On Fri, Jan 09, 2026 at 10:31:57AM +0000, Teddy Astie wrote:
> > It would be easier to not use hvmloader, especially since only UEFI 
> > supports SEV and guests would still need to support (Xen-specific) SEV 
> > bits to begin with.
> 
> I would be very happy to relegate hvmloader to be used with SeaBIOS
> only, and to load OVMF directly for HVM guests.  But I don't know
> what's missing for OVMF to be capable of that.  I would think not
> much, since it's already almost working for PVH guests AFAIK.

OvmfXen works in PVH, and you can start guest ;-), the last change was
to remove the use of the hypercall page so the shutdown hypercall could
be called from UEFI Runtime Service.

> Maybe PCI enumeration, but OVMF must have a way of doing that already
> for other platforms I expect.

Yes, that would probably be the main thing, I believe. It might just be
a setting to enable enumeration when OvmfXen is started via the PVH
entry point, I haven't really try to boot OVMF in HVM without hvmloader
yet, and we would need to change the tool stack to boot an HVM guest via
the PVH entry point.

But, I already have a prototype of OvmfXen that could boot (modified)
Linux in an SEV guest, it's based on SEV work from sometime ago so might
not work anymore (and I don't remember if linux could start userspace):

https://xenbits.xenproject.org/gitweb/?p=people/aperard/ovmf.git;a=log;h=refs/heads/wip.sev

Cheers,

-- 
Anthony PERARD