Avihai Horon <avih...@nvidia.com> wrote: > On 15/02/2023 14:43, Juan Quintela wrote: >> External email: Use caution opening links or attachments >> >> >> Avihai Horon <avih...@nvidia.com> wrote: >>> Currently, if IOMMU of a VFIO container doesn't support dirty page >>> tracking, migration is blocked. This is because a DMA-able VFIO device >>> can dirty RAM pages without updating QEMU about it, thus breaking the >>> migration. >>> >>> However, this doesn't mean that migration can't be done at all. >>> In such case, allow migration and let QEMU VFIO code mark all pages >>> dirty. >>> >>> This guarantees that all pages that might have gotten dirty are reported >>> back, and thus guarantees a valid migration even without VFIO IOMMU >>> dirty tracking support. >>> >>> The motivation for this patch is the introduction of iommufd [1]. >>> iommufd can directly implement the /dev/vfio/vfio container IOCTLs by >>> mapping them into its internal ops, allowing the usage of these IOCTLs >>> over iommufd. However, VFIO IOMMU dirty tracking is not supported by >>> this VFIO compatibility API. >>> >>> This patch will allow migration by hosts that use the VFIO compatibility >>> API and prevent migration regressions caused by the lack of VFIO IOMMU >>> dirty tracking support. >>> >>> [1] >>> https://lore.kernel.org/kvm/0-v6-a196d26f289e+11787-iommufd_...@nvidia.com/ >>> >>> Signed-off-by: Avihai Horon <avih...@nvidia.com> >>> Reviewed-by: Cédric Le Goater <c...@redhat.com> >> Reviewed-by: Juan Quintela <quint...@redhat.com> >> >> I know why you are doing this. >> >> But I think this should print a warning, error, somewhere. > > IMHO, I'm not sure it's really necessary. > > To enable VFIO migration the user must explicitly set x-enable-migration=on. > I guess in this case the user is well aware of the dirty tracking > capabilities the VFIO device has or doesn't have. > So I don't think adding this error/warning will help much.
Oops. I missed that bit. I retire my objection. Sorry, Juan. > Thanks. > >> >> You are just dirtying all pages each time we arrive here. >> >> Even calling the featura "experimental" is an understatement. >> >> Later, Juan. >>
