Paolo Bonzini <pbonz...@redhat.com> wrote: > > > On 05/07/2016 18:27, Nadav Amit wrote: >>> Although such hardware is old, there are some hypervisors that do not set >>> the ecap.coherency of emulated IOMMUs. Yes, it is unwise, but there is no >>> reason to further punish these hypervisors. > > QEMU will need the kernel to respect ecap.coherency in order to support > nested VFIO, for example.
To clarify - the kernel respects the coherency, but performs more clflushes than necessary. It has no functional impact, but induces performance degradation (which I did not measure, but is likely to be several hundreds of cycles per flush). Regards, Nadav _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
