On 04.12.20 06:44, David Gibson wrote:
> The default behaviour for virtio devices is not to use the platforms normal
> DMA paths, but instead to use the fact that it's running in a hypervisor
> to directly access guest memory. That doesn't work if the guest's memory
> is protected from hypervisor access, such as with AMD's SEV or POWER's PEF.
>
> So, if a securable guest memory mechanism is enabled, then apply the
> iommu_platform=on option so it will go through normal DMA mechanisms.
> Those will presumably have some way of marking memory as shared with
> the hypervisor or hardware so that DMA will work.
>
> Signed-off-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx>
> ---
> hw/core/machine.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index a67a27d03c..d16273d75d 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -28,6 +28,8 @@
> #include "hw/mem/nvdimm.h"
> #include "migration/vmstate.h"
> #include "exec/securable-guest-memory.h"
> +#include "hw/virtio/virtio.h"
> +#include "hw/virtio/virtio-pci.h"
>
> GlobalProperty hw_compat_5_1[] = {
> { "vhost-scsi", "num_queues", "1"},
> @@ -1169,6 +1171,17 @@ void machine_run_board_init(MachineState *machine)
> * areas.
> */
> machine_set_mem_merge(OBJECT(machine), false, &error_abort);
> +
> + /*
> + * Virtio devices can't count on directly accessing guest
> + * memory, so they need iommu_platform=on to use normal DMA
> + * mechanisms. That requires also disabling legacy virtio
> + * support for those virtio pci devices which allow it.
> + */
> + object_register_sugar_prop(TYPE_VIRTIO_PCI, "disable-legacy",
> + "on", true);
> + object_register_sugar_prop(TYPE_VIRTIO_DEVICE, "iommu_platform",
> + "on", false);
I have not followed all the history (sorry). Should we also set iommu_platform
for virtio-ccw? Halil?
