[PATCH v3 1/2] spapr: Disable legacy virtio devices for pseries-5.0 and later

[David Gibson]

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 <da...@gibson.dropbear.id.au>
---
 hw/ppc/spapr.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 2eb0d8f70d..3cfc98ac61 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"
 
@@ -4566,8 +4567,20 @@ static const TypeInfo spapr_machine_info = {
 
 static void spapr_machine_latest_class_options(MachineClass *mc)
 {
+    /*
+     * 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.  We can't do that from the base
+     * class since it doesn't have a compat_props.
+     */
+    static GlobalProperty compat[] = {
+        { TYPE_VIRTIO_PCI, "disable-legacy", "on", },
+    };
+
     mc->alias = "pseries";
     mc->is_default = true;
+
+    compat_props_add(mc->compat_props, compat, G_N_ELEMENTS(compat));
 }
 
 #define DEFINE_SPAPR_MACHINE(suffix, verstr, latest)                 \
@@ -4607,6 +4620,9 @@ 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);
@@ -4614,6 +4630,7 @@ static void spapr_machine_4_2_class_options(MachineClass 
*mc)
     smc->default_caps.caps[SPAPR_CAP_FWNMI_MCE] = SPAPR_CAP_OFF;
     smc->rma_limit = 16 * GiB;
     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