On 2018/4/6 17:36, Peter Maydell wrote: > On 5 April 2018 at 15:22, Peter Maydell <peter.mayd...@linaro.org> wrote: >> > On 29 March 2018 at 11:54, Peter Maydell <peter.mayd...@linaro.org> wrote: >>> >> On 23 March 2018 at 12:08, Peter Maydell <peter.mayd...@linaro.org> >>> >> wrote: >>>> >>> On 21 March 2018 at 08:00, Shannon Zhao <zhaoshengl...@huawei.com> >>>> >>> wrote: >>>>> >>>> On 2018/3/20 19:54, Peter Maydell wrote: >>>>>> >>>>> Can you still successfully migrate a VM from a QEMU version >>>>>> >>>>> without this bugfix to one with the bugfix ? >>>>>> >>>>> >>>>> >>>> I've tested this case. I can migrate a VM between these two versions. >>>> >>> >>>> >>> Hmm. Looking at the code I can't see how that would work, >>>> >>> except by accident. Let me see if I understand what's happening >>>> >>> here: >> > >>> >> I was thinking a bit more about how to handle this, and >>> >> my best idea was: >>> >> >>> >> (1) send something in the migration stream that says >>> >> "I don't have this bug" (version number change? >>> >> vmstate field that's just a "no bug" flag? subsection >>> >> with no contents?) >>> >> >>> >> (2) on the destination, if the source doesn't tell us >>> >> it doesn't have this bug, and we are running KVM, then >>> >> shift all the data in the arrays down to fix it up >>> >> [Strictly what we want to know is if the source is >>> >> running KVM, not if the destination is, but I don't >>> >> know of a way to find that out, and in practice TCG->KVM >>> >> migrations don't work anyway, so it's not a big deal.] >> > >> > Shannon, are you planning to look at this for 2.12, or should >> > we postpone it to 2.13? (It's not a regression, right? So >> > we don't necessarily have to urgently fix it for 2.12.) > On reflection, I think I'd aim for 2.13 for this, since: > * it's not a regression > * it doesn't actually affect any of our boards, because > none of them define enough interrupt lines that they > would actually be using the top 32 that we fail to migrate > * getting the migration compat right is a bit tricky and > will benefit from having the time for careful review and testing > > Let me know if I'm wrong with any of those assumptions. Yes, it's no need to merge this for 2.12. I'll respin this patch later.
Thanks, -- Shannon
