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. thanks -- PMM
