On Tue, May 19, 2026 at 3:00 PM David Woodhouse <[email protected]> wrote: > Or some guest configurations which have only ever been tested under KVM > could have a bug where they *rely* on the registers not being writable, > and write values which are inconsistent with the rest of their > configuration. Which breaks the moment those registers become writable.
Yeah, just having guests that worked by utter chance - but you still don't want to break them - is the case that is most likely. Crappy code that runs only under emulation/virtualization appears with probability 1 over time. Is this likely in this specific case---probably not, honestly. Christoffer's patch dates back to 2018 (commit d53c2c29ae0d); *back then* KVM/Arm was a lot less mature, and people developing for Arm on vanilla upstream kernels have moved on from Linux 4.19. I would still lean towards accepting the code considering the limited complexity of the addition (in fact I like it more now that it uses IIDR instead of v2_groups_user_writable, but that's taste). However, there's a huge difference between setting expectations based on 2018 vs 2026 maturity, and perhaps that's why Marc overall is inclined to put this in the category of pointless bug for bug compatibility? In any case, there's no arguing over this documentation patch, which is already a good thing to know. Thanks, Paolo > And those hypothetical cases *do* happen. All of the time. There's a > massive zoo of guest operating systems; not just the major players like > Linux, FreeBSD and Windows but a whole bunch of embedded home-grown and > network appliance kernels. > > Nobody is claiming that we shouldn't fix any bug ever.
