On Fri, Dec 14, 2018 at 10:43:03AM +0800, Jason Wang wrote: > > On 2018/12/13 下午10:31, Michael S. Tsirkin wrote: > > > Just to make sure I understand this. It looks to me we should: > > > > > > - allow passing GIOVA->GPA through UAPI > > > > > > - cache GIOVA->GPA somewhere but still use GIOVA->HVA in device IOTLB for > > > performance > > > > > > Is this what you suggest? > > > > > > Thanks > > Not really. We already have GPA->HVA, so I suggested a flag to pass > > GIOVA->GPA in the IOTLB. > > > > This has advantages for security since a single table needs > > then to be validated to ensure guest does not corrupt > > QEMU memory. > > > > I wonder how much we can gain through this. Currently, qemu IOMMU gives > GIOVA->GPA mapping, and qemu vhost code will translate GPA to HVA then pass > GIOVA->HVA to vhost. It looks no difference to me. > > Thanks The difference is in security not in performance. Getting a bad HVA corrupts QEMU memory and it might be guest controlled. Very risky. If translations to HVA are done in a single place through a single table it's safer as there's a single risky place. -- MST
