On 03/16/2012 03:55 PM, Takuya Yoshikawa wrote: > On Fri, 16 Mar 2012 15:30:45 +0800 > Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> wrote: > >>>> There is a example: >>>> >>>> CPU A CPU B >>>> guest page is written by write-emulation >>>> >>>> hold mmu-lock and see dirty-bitmap >>>> is not be changed, then migration is >>>> completed. >>> >>> We do not allow this break. >>> >> >> >> Hmm? what can avoid this? Could you please point it out? > > Stopping the guest before actualy migrating the guest means VCPU threads > must be back in the userspace at the moment, no? > > So when the final GET_DIRTY_LOG is being executed, thread A cannot be > in KVM. > >> The problem is the guest page is written before dirty-bitmap is set, >> we may log the dirty page in this window like above case... > > Exactly, but the next GET_DIRTY_LOG call can take that because, as I > wrote above, at this time the GET_DIRTY_LOG must not be the final one. > Thanks for your explanation, maybe you are right, i do not know migration much. What i worried about is, you have changed the behaviour of GET_DIRTY_LOG, in the current one, it can get all the dirty pages when it is called; after your change, GET_DIRTY_LOG can get a empty dirty bitmap but dirty page exists. Migration may work correctly depends on the final GET_DIRTY_LOG, in that time, guest is stopped. But i am not sure whether other components using GET_DIRTY_LOG are happy, e.g. frame-buffer. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
