[Qemu-devel] [PATCH v6 15/16] virtio-pci: increase the maximum number of virtqueues to 513

[Jason Wang <jasowang@redhat.com>]

This patch increases the maximum number of virtqueues for pci from 64
to 513. This will allow booting a virtio-net-pci device with 256 queue
pairs on recent Linux host (which supports up to 256 tuntap queue pairs).

To keep migration compatibility, 64 was kept for legacy machine
types. This is because qemu in fact allows guest to probe the limit of
virtqueues through trying to set queue_sel. So for legacy machine
type, we should make sure setting queue_sel to more than 63 won't
make effect.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Alexander Graf <agraf@suse.de>
Cc: qemu-ppc@nongnu.org
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 hw/i386/pc_piix.c      | 5 +++++
 hw/i386/pc_q35.c       | 5 +++++
 hw/ppc/spapr.c         | 5 +++++
 hw/virtio/virtio-pci.c | 3 ++-
 4 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 212e263..6e098ce 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -49,6 +49,7 @@
 #include "hw/acpi/acpi.h"
 #include "cpu.h"
 #include "qemu/error-report.h"
+#include "hw/virtio/virtio-bus.h"
 #ifdef CONFIG_XEN
 #  include <xen/hvm/hvm_info_table.h>
 #endif
@@ -312,6 +313,10 @@ static void pc_init_pci(MachineState *machine)
 
 static void pc_compat_2_3(MachineState *machine)
 {
+    ObjectClass *klass = object_class_by_name("virtio-pci-bus");
+    VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);
+
+    k->queue_max = 64;
 }
 
 static void pc_compat_2_2(MachineState *machine)
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index e67f2de..ff7c414 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -45,6 +45,7 @@
 #include "hw/usb.h"
 #include "hw/cpu/icc_bus.h"
 #include "qemu/error-report.h"
+#include "include/hw/virtio/virtio-bus.h"
 
 /* ICH9 AHCI has 6 ports */
 #define MAX_SATA_PORTS     6
@@ -291,6 +292,10 @@ static void pc_q35_init(MachineState *machine)
 
 static void pc_compat_2_3(MachineState *machine)
 {
+    ObjectClass *klass = object_class_by_name("virtio-pci-bus");
+    VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);
+
+    k->queue_max = 64;
 }
 
 static void pc_compat_2_2(MachineState *machine)
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 8e43aa2..ee8f6a3 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -50,6 +50,7 @@
 #include "hw/pci/pci.h"
 #include "hw/scsi/scsi.h"
 #include "hw/virtio/virtio-scsi.h"
+#include "hw/virtio/virtio-bus.h"
 
 #include "exec/address-spaces.h"
 #include "hw/usb.h"
@@ -1827,6 +1828,10 @@ static const TypeInfo spapr_machine_info = {
 
 static void spapr_compat_2_3(Object *obj)
 {
+    ObjectClass *klass = object_class_by_name("virtio-pci-bus");
+    VirtioBusClass *k = VIRTIO_BUS_CLASS(klass);
+
+    k->queue_max = 64;
 }
 
 static void spapr_compat_2_2(Object *obj)
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 7d01500..500d6db 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -42,7 +42,8 @@
  * configuration space */
 #define VIRTIO_PCI_CONFIG_SIZE(dev)     VIRTIO_PCI_CONFIG_OFF(msix_enabled(dev))
 
-#define VIRTIO_PCI_QUEUE_MAX 64
+/* 513 is for the kernel limit for the maximum number of tuntap queues - 256 */
+#define VIRTIO_PCI_QUEUE_MAX 513
 
 static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size,
                                VirtIOPCIProxy *dev);
-- 
2.1.0