On Thu, Feb 20, 2020 at 05:06:04PM +0100, Halil Pasic wrote: > * This usage is not congruent with standardised semantics of > VIRTIO_F_IOMMU_PLATFORM. Guest memory protected is an orthogonal reason > for using DMA API in virtio (orthogonal with respect to what is > expressed by VIRTIO_F_IOMMU_PLATFORM). Quoting the spec: \item[VIRTIO_F_ACCESS_PLATFORM(33)] This feature indicates that the device can be used on a platform where device access to data in memory is limited and/or translated. E.g. this is the case if the device can be located behind an IOMMU that translates bus addresses from the device into physical addresses in memory, if the device can be limited to only access certain memory addresses or if special commands such as a cache flush can be needed to synchronise data in memory with the device. Whether accesses are actually limited or translated is described by platform-specific means. If this feature bit is set to 0, then the device has same access to memory addresses supplied to it as the driver has. In particular, the device will always use physical addresses matching addresses used by the driver (typically meaning physical addresses used by the CPU) and not translated further, and can access any address supplied to it by the driver. When clear, this overrides any platform-specific description of whether device access is limited or translated in any way, e.g. whether an IOMMU may be present. since device can't access encrypted memory, this seems to match your case reasonably well. -- MST
