On Sat, 2012-06-09 at 20:53 +1000, Benjamin Herrenschmidt wrote: > Hi folks !
(After some discussion with Andreas ...) > I'm looking at sorting out the state save/restore of target-ppc (which > means understanding in general how it works in qemu :-) > > So far I've somewhat figured out that there's the "old way" where we > just provide a "bulk" save/restore function pair, and the "new way" > where we have nicely tagged field lists etc... > > x86 seems to use the later for the CPU state, ppc is a mess and uses the > former with interesting incompatible format change depending on how qemu > is build :-) So I think that's one area I need to fix. Ok, so I'm told there are patches to convert ppc, I haven't seen them in my list archives, so if somebody has a pointer, please shoot, that will save me some work :-) .../... > What I'd need is something in spapr that can be used to "resync" bits of > the cpu state with the external htab that gets run after everything is > loaded and before emulation restarts. > > Any idea how to do that properly ? I suppose I could also try to iterate > all the vcpu's after loading the hash table & update the fields but not > only that's gross ... I also don't know how to do it :-) So I did an experiment using the "old style" save/restore (bad boy !) and got that part to work by just iterating the vcpu's. It's a bit nasty but it's the right way I think, ie, what we have here (the external hash table) is a global object under control/ownership of the platform code for which a pointer is cached in the CPU state (so the mmu emulation gets to it easily), so those cached pointers need to be updated in all CPUs when a new hash table is loaded/allocated. That leads to another question however... I need to add save/restore to a bunch more stuff such as the xics (interrupt controller), the various spapr devices, etc... So far the VMState stuff is all nice if you have fixed sized arrays. However I haven't quite found out the right way to use it for things like: - The hash table (mentioned above). This is just a big chunk of memory (it will routinely be 16M), so I really don't want to start iterating all elements, just a bulk load will do, and the size might actually be variable. - The XICS (interrupt controller). The actual size of the interrupt state array can vary (the number of interrupt sources can vary, it's fixed today by the machine code but I wouldn't rely too much on that and in any case, from the XICS driver perspective, it's not a constant, it's a variable it gets passed when initializing). So in both these cases, I need either code to control the save/load process (old style ? hard to hook into vmstate as far as I can tell) or maybe a way to describe the array so that the array size itself is a pointer to a variable (Andreas mentioned something along those lines). Is there any doco for that stuff btw ? I haven't seen anything detailed... Suggestions ? Cheers, Ben.
