* Peter Maydell (peter.mayd...@linaro.org) wrote: > On 17 July 2017 at 19:58, Dr. David Alan Gilbert <dgilb...@redhat.com> wrote: > > * Edgar E. Iglesias (edgar.igles...@gmail.com) wrote: > >> Is there a way we can prevent migration of the RAMBlock? > > > > Not yet, I think we'd have to: > > a) Add a flag to the RAMBlock > > b) Set it/clear it on registration > > c) Have a RAMBLOCK_FOREACH_MIGRATABLE macro > > d) Replace all of the RAMBLOCK_FOREACH (and the couple of hand coded > > cases) with the RAMBLOCK_FOREACH_MIGRATABLE > > e) Worry about the corner cases! > > > > I've got a few worries about what happens when the kernel tries to > > do dirty yncing - I'm not sure if we have to change anything on that > > interface to skip those RAMBlocks. > > OK, so what should we do for 2.10 ? > > We could: > * implement the changes you suggest above, and mark only > vmstate_register_ram'd blocks as migratable > (would probably need to fix some places which buggily > don't call vmstate_register_ram) > * implement the changes above, but special case mmio-interface > so only its ramblock is marked unmigratable
I think either of these is too late for 2.10 - I don't fancy prodding about in all of the migration RAM loops at this stage. > * postpone the changes above until 2.11, and for 2.10 register > a migration-blocker in mmio-interface so that we at least > give the user a useful error rather than having it fail > obscurely on vmload (and release note this) I think that's best, especially because I've just thought of another nasty. If I understand the way mmio-interface is working, you're dynamically changing the RAMBlock list while the guest is running. And while we are using QLIST_FOREACH_RCU I'm not convinced we're actually safe against dynamic modification of that list. > (Or something else?) > > I do think we definitely need to fix this for 2.11 at latest. OK, I can do a-e OK, I'm more worried now about that dynamic modification I just thought of. Dave > thanks > -- PMM -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
