On Tue, Dec 4, 2018 at 8:30 PM Jason Wang <jasow...@redhat.com> wrote: > > > On 2018/12/5 上午2:37, Jintack Lim wrote: > > Hi, > > > > I'm wondering how the current implementation works when logging dirty > > pages during migration from vhost-net (in kernel) when used vIOMMU. > > > > I understand how vhost-net logs GPAs when not using vIOMMU. But when > > we use vhost with vIOMMU, then shouldn't vhost-net need to log the > > translated address (GPA) instead of the address written in the > > descriptor (IOVA) ? The current implementation looks like vhost-net > > just logs IOVA without translation in vhost_get_vq_desc() in > > drivers/vhost/net.c. It seems like QEMU doesn't do any further > > translation of the dirty log when syncing. > > > > I might be missing something. Could somebody shed some light on this? > > > Good catch. It looks like a bug to me. Want to post a patch for this?
Thanks for the confirmation. What would be a good setup to catch this kind of migration bug? I tried to observe it in the VM expecting to see network applications not getting data correctly on the destination, but it was not successful (i.e. the VM on the destination just worked fine.) I didn't even see anything going wrong when I disabled the vhost logging completely without using vIOMMU. What I did is I ran multiple network benchmarks (e.g. netperf tcp stream and my own one to check correctness of received data) in a VM without vhost dirty page logging, and the benchmarks just ran fine in the destination. I checked the used ring at the time the VM is stopped in the source for migration, and it had multiple descriptors that is (probably) not processed in the VM yet. Do you have any insight how it could just work and what would be a good setup to catch this? About sending a patch, as Michael suggested, I think it's better for you to handle this case - this is not my area of expertise, yet :-) > > Thanks > > > > > > Thanks, > > Jintack > > > > >
