Re: [XEN PATCH] x86/hvm: make ACPI PM timer support optional

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

On Wed, Sep 18, 2024 at 12:29:39PM +0300, Sergiy Kibrik wrote:
> 16.09.24 22:57, Stefano Stabellini:
> > On Mon, 16 Sep 2024, Roger Pau Monné wrote:
> > > On Mon, Sep 16, 2024 at 09:37:57AM +0300, Sergiy Kibrik wrote:
> > > > Introduce config option X86_PMTIMER so that pmtimer driver can be 
> > > > disabled on
> > > > systems that don't need it.
> > > 
> > > Same comment as in the VGA patch, you need to handle the user passing
> > > X86_EMU_PM.  It's not OK to just ignore the flag if the hypervisor is
> > > built without ACPI PM timer support.
> > 
> > I also think that the flag should not be ignored. I think that Xen
> > should return error if a user is passing a domain feature not supported
> > by a particular version of the Xen build. I don't think that libxl needs
> > to be changed as part of this patch necessarily.
> 
> It looks like toolstack always leaves X86_EMU_PM bit enabled, so that part
> may also require changes.

I think you will be unable to create HVM guests, but that's kind of
expected if ACPI PM emulation is removed from the hypervisor (it won't
be an HVM guest anymore if it doesn't have ACPI PM).

PVH guest don't set X86_EMU_PM so you should be able to create those
fine.

Thanks, Roger.