Hi Paolo, On Thu, Jul 21, 2022 at 01:47:02PM +0200, Paolo Bonzini wrote: > On 7/21/22 13:00, Michael S. Tsirkin wrote: > > Well why not. > > > > Reviewed-by: Michael S. Tsirkin<m...@redhat.com> > > > > who's merging this? Paolo me or you? > > I don't think this should be merged as is. > > The linuxboot ROM takes the data from fw_cfg, and (with the exception of > ACPI tables) that data is not migrated. Because reading it into the > guest is not atomic, both sides must match. This version of the patches > at least doesn't move the preexisting DTB entry of the setup_data, but > it still has a mismatching size and that can be a problem when migrating > backwards.
As discussed online, this seems absolutely preposterous and will never happen anywhere real ever at all. Trying to account for it is adding needless complexity for no real world benefit; it's the type of thinking that results in a mess. Further, conditionalizing the RNG seed on something else means fewer users receive the increased security of having an early boottime seed. This seems like a silly direction go go in. But to assess things in the open here: - On upgrades, there's no problem because the old bytes don't move. - On downgrades, there's mostly no problem because next will point to 0. - On downgrade there could be some ridiculous theoretical problem if the reader has already read a non-zero next. But this will never actually happen in practice. So we really should just stick with the simple and straight forward path that this v6 accomplishes, and not muck things up with stupidity. Jason
