[PATCH v2 1/2] spapr: Disable legacy virtio devices for pseries-5.0 and later

[David Gibson <david@gibson.dropbear.id.au>]

PAPR specifies a kind of odd, paravirtualized PCI bus, which looks to
the guess mostly like classic PCI, even if some of the individual
devices on the bus are PCI Express.  One consequence of that is that
virtio-pci devices still default to being in transitional mode, though
legacy mode is now disabled by default on current q35 x86 machine
types.

Legacy mode virtio devices aren't really necessary any more, and are
causing some problems for future changes.  Therefore, for the
pseries-5.0 machine type (and onwards), switch to modern-only
virtio-pci devices by default.

This does mean we no longer support guest kernels prior to 4.0, unless
they have modern virtio support backported (which some distro kernels
like that in RHEL7 do).

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 hw/ppc/spapr.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index cb220fde45..6e1e467cc6 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -65,6 +65,7 @@
 
 #include "hw/pci/pci.h"
 #include "hw/scsi/scsi.h"
+#include "hw/virtio/virtio-pci.h"
 #include "hw/virtio/virtio-scsi.h"
 #include "hw/virtio/vhost-scsi-common.h"
 
@@ -4567,7 +4568,14 @@ static void spapr_machine_latest_class_options(MachineClass *mc)
  */
 static void spapr_machine_5_0_class_options(MachineClass *mc)
 {
-    /* Defaults for the latest behaviour inherited from the base class */
+    /* Most defaults for the latest behaviour are inherited from the
+     * base class, but we need to override the (non ppc specific)
+     * default behaviour for virtio */
+    static GlobalProperty compat[] = {
+        { TYPE_VIRTIO_PCI, "disable-legacy", "on", },
+    };
+
+    compat_props_add(mc->compat_props, compat, G_N_ELEMENTS(compat));
 }
 
 DEFINE_SPAPR_MACHINE(5_0, "5.0", true);
@@ -4578,12 +4586,16 @@ DEFINE_SPAPR_MACHINE(5_0, "5.0", true);
 static void spapr_machine_4_2_class_options(MachineClass *mc)
 {
     SpaprMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
+    static GlobalProperty compat[] = {
+        { TYPE_VIRTIO_PCI, "disable-legacy", "auto" },
+    };
 
     spapr_machine_5_0_class_options(mc);
     compat_props_add(mc->compat_props, hw_compat_4_2, hw_compat_4_2_len);
     smc->default_caps.caps[SPAPR_CAP_CCF_ASSIST] = SPAPR_CAP_OFF;
     smc->default_caps.caps[SPAPR_CAP_FWNMI_MCE] = SPAPR_CAP_OFF;
     mc->nvdimm_supported = false;
+    compat_props_add(mc->compat_props, compat, G_N_ELEMENTS(compat));
 }
 
 DEFINE_SPAPR_MACHINE(4_2, "4.2", false);
-- 
2.24.1