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Re: [Xen-devel] [Xen 4.12 bug] HVM/PVH boot confusion

On Wed, Jan 30, 2019 at 12:30:44PM +0000, Andrew Cooper wrote:
> >> There are at least two bugs here.
> >>
> >> 1) RSDP was a late addition to the PVH boot protocol.  Xen's PVH
> >> entrypoint must not mandate its existence, because there are releases of
> >> the domain builder which don't provide it.
> > The inner Xen, in this case, can fall back to scanning low 1MB memory
> > for RSDP.
> Agreed.
> >
> >> 2) The HVM/PVH boot confusion.  This think this is a still-outstanding
> >> bug around the broken assumption that the hvmloader binary speaks the
> >> PVH protocol without advertising itself appropriately (I really regret
> >> not objecting to those patches before they went in).  At the least, that
> >> needs fixing by putting a proper ELF note in hvmloader, and the domain
> >> builder needs to be updated to build all PVH-boot-ABI images consistently.
> > Do you expect users to drop an arbitrary hvmloader into an arbitrary
> > version of Xen and they continue to work?
> This is hard to answer.  HVMLoader specifically, perhaps not.  After
> all, it does link unstable libraries from tools/

That's my thought as well.

To me it would be nice to make hvmloader a proper PVH binary, but this
task's priority is rather low, because I consider it internal to Xen.

> That said, how we boot guests is an ABI, and this should be kept in mind
> when making changes.

Sure. I agree.

I think we've been mindful in that regard. Domain builder code isn't
perfect, but it doesn't remove or add to the ABI willy-nilly. Long term
I agree with Roger -- things can be streamlined.

Your use case is rather special. At this moment I think if we fix issue
bug #1 you should be good to go?


> ~Andrew

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