On 29 January 2018 at 09:53, Dr. David Alan Gilbert <dgilb...@redhat.com> wrote: > * Peter Maydell (peter.mayd...@linaro.org) wrote: >> On 26 January 2018 at 19:46, Dr. David Alan Gilbert <dgilb...@redhat.com> >> wrote: >> > * Peter Maydell (peter.mayd...@linaro.org) wrote: >> >> I think the correct fix here is that your test code should turn >> >> its MMU on. Trying to treat guest RAM as uncacheable doesn't work >> >> for Arm KVM guests (for the same reason that VGA device video memory >> >> doesn't work). If it's RAM your guest has to arrange to map it as >> >> Normal Cacheable, and then everything should work fine. >> > >> > Does this cause problems with migrating at just the wrong point during >> > a VM boot? >> >> It wouldn't surprise me if it did, but I don't think I've ever >> tried to provoke that problem... > > If you think it'll get the RAM contents wrong, it might be best to fail > the migration if you can detect the cache is disabled in the guest.
I guess QEMU could look at the value of the "MMU disabled/enabled" bit in the guest's system registers, and refuse migration if it's off... (cc'd Marc, Christoffer to check that I don't have the wrong end of the stick about how thin the ice is in the period before the guest turns on its MMU...) thanks -- PMM
