path: root/hw
diff options
authorDavid Gibson <david@gibson.dropbear.id.au>2020-06-04 14:20:24 +1000
committerDavid Gibson <david@gibson.dropbear.id.au>2021-02-08 16:57:38 +1100
commit9f88a7a3df11a5aaa6212ea535d40d5f92561683 (patch)
treef2505dd7d9e87c4f4f96e84143fb63be20b088b2 /hw
parent6742eefc9314678bba39e461fe8cdd0a841c3e92 (diff)
confidential guest support: Alter virtio default properties for protected guests
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 confidential guest 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@gibson.dropbear.id.au> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Greg Kurz <groug@kaod.org>
Diffstat (limited to 'hw')
1 files changed, 13 insertions, 0 deletions
diff --git a/hw/core/machine.c b/hw/core/machine.c
index f45a795478..970046f438 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -33,6 +33,8 @@
#include "migration/global_state.h"
#include "migration/vmstate.h"
#include "exec/confidential-guest-support.h"
+#include "hw/virtio/virtio.h"
+#include "hw/virtio/virtio-pci.h"
GlobalProperty hw_compat_5_2[] = {};
const size_t hw_compat_5_2_len = G_N_ELEMENTS(hw_compat_5_2);
@@ -1196,6 +1198,17 @@ 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);