On Thu, Aug 06, 2020 at 03:27:38PM +0800, Jason Wang wrote: > > On 2020/8/6 下午1:53, Michael S. Tsirkin wrote: > > On Thu, Aug 06, 2020 at 11:23:05AM +0800, Jason Wang wrote: > > > On 2020/8/5 下午7:40, Michael S. Tsirkin wrote: > > > > On Wed, Aug 05, 2020 at 02:14:07PM +0800, Jason Wang wrote: > > > > > On 2020/8/4 上午5:00, Michael S. Tsirkin wrote: > > > > > > Some legacy guests just assume features are 0 after reset. > > > > > > We detect that config space is accessed before features are > > > > > > set and set features to 0 automatically. > > > > > > Note: some legacy guests might not even access config space, if this is > > > > > > reported in the field we might need to catch a kick to handle these. > > > > > I wonder whether it's easier to just support modern device? > > > > > > > > > > Thanks > > > > Well hardware vendors are I think interested in supporting legacy > > > > guests. Limiting vdpa to modern only would make it uncompetitive. > > > > > > My understanding is that, IOMMU_PLATFORM is mandatory for hardware vDPA to > > > work. > > Hmm I don't really see why. Assume host maps guest memory properly, > > VM does not have an IOMMU, legacy guest can just work. > > > Yes, guest may not set IOMMU_PLATFORM. > > > > > > Care explaining what's wrong with this picture? > > > The problem is virtio_vdpa, without IOMMU_PLATFORM it uses PA which can not > work if IOMMU is enabled. > > Thanks So that's a virtio_vdpa limitation. In the same way, if a device does not have an on-device iommu *and* is not behind an iommu, then vdpa can't bind to it. But this virtio_vdpa specific hack does not belong in a generic vdpa code. > > > > > > > > So it can only work for modern device ... > > > > > > Thanks > > > > > > > > > > > > > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
