On Sat, Jul 25, 2026 at 12:45:08PM +0900, Akihiko Odaki wrote: > I also hope this could fix vhost-user for TCG: > https://gitlab.com/qemu-project/qemu/-/work_items/2092 > > Perhaps the memory isolation should be enabled by default for TCG.
If I understand the bug correctly, TCG needs the dirty bitmap to be up-to-date and vhost-user's dirty logging mechanism does not suffice. Memory isolation would keep the dirty bitmap up-to-date but copying data between guest RAM and the isolated memory would add overhead. For the TCG use case it should be possible to use just vhost-shadow-virtqueue.c without isolated memory so that vhost_svq_flush() -> virtqueue_fill() -> virtqueue_unmap_sg() -> dma_memory_unmap() keeps the dirty bitmap updated. There is still an overhead because the virtqueue kick/call is intercepted by QEMU, but there is no memcpy. The TCG use case is something that could be tackled once memory isolation is finished. If no one has time to implement the pure svq solution for TCG, then memory isolation could be used in any case. Stefan
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