On 2015/12/31 15:13, Jason Wang wrote:
This patch tries to implement an device IOTLB for vhost. This could be used with for co-operation with userspace(qemu) implementation of iommu for a secure DMA environment in guest. The idea is simple. When vhost meets an IOTLB miss, it will request the assistance of userspace to do the translation, this is done through: - Fill the translation request in a preset userspace address (This address is set through ioctl VHOST_SET_IOTLB_REQUEST_ENTRY). - Notify userspace through eventfd (This eventfd was set through ioctl VHOST_SET_IOTLB_FD). When userspace finishes the translation, it will update the vhost IOTLB through VHOST_UPDATE_IOTLB ioctl. Userspace is also in charge of snooping the IOTLB invalidation of IOMMU IOTLB and use VHOST_UPDATE_IOTLB to invalidate the possible entry in vhost.
Is there any performance data shows the difference with IOTLB supporting? I doubt we may see performance decrease since the flush code path is longer than before.
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