On 2025/07/24 4:31, Paolo Abeni wrote:
Extend the features configuration space to 128 bits. If the virtio
device supports any extended features, allow the common read/write
operation to access all of it, otherwise keep exposing only the
lower 64 bits.
On migration, save the 128 bit version of the features only if the
upper bits are non zero. Relay on reset to clear all the feature
space before load.
Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
v3 -> v4:
- use new virtio_features macro names
- move the build bug before vmstate_virtio_pci_modern_state_sub
v2 -> v3:
- drop the pre_load/post_load trickery and relay on reset zeroing
the features instead.
- avoid union usage, just increase guest_features size and use
SUB_ARRAY.
- drop unneeded '!!'
- _array -> _ex
v1 -> v2:
- use separate VMStateDescription and pre/post load to avoid breaking
migration
- clear proxy features on device reset
---
hw/virtio/virtio-pci.c | 69 +++++++++++++++++++++++++++++-----
include/hw/virtio/virtio-pci.h | 2 +-
2 files changed, 61 insertions(+), 10 deletions(-)
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 767216d795..bcc4d48c2c 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -109,6 +109,29 @@ static const VMStateDescription
vmstate_virtio_pci_modern_queue_state = {
}
};
+static bool virtio_pci_modern_state_features128_needed(void *opaque)
+{
+ VirtIOPCIProxy *proxy = opaque;
+ uint32_t features = 0;
+ int i;
+
+ for (i = 2; i < ARRAY_SIZE(proxy->guest_features); ++i) {
+ features |= proxy->guest_features[i];
+ }
+ return features;
+}
+
+static const VMStateDescription vmstate_virtio_pci_modern_state_features128 = {
+ .name = "virtio_pci/modern_state/features128",
+ .version_id = 1,
+ .minimum_version_id = 1,
+ .needed = &virtio_pci_modern_state_features128_needed,
+ .fields = (const VMStateField[]) {
+ VMSTATE_UINT32_SUB_ARRAY(guest_features, VirtIOPCIProxy, 2, 2),
+ VMSTATE_END_OF_LIST()
+ }
+};
+
static bool virtio_pci_modern_state_needed(void *opaque)
{
VirtIOPCIProxy *proxy = opaque;
@@ -116,6 +139,11 @@ static bool virtio_pci_modern_state_needed(void *opaque)
return virtio_pci_modern(proxy);
}
+/*
+ * Avoid silently breaking migration should the feature space increase
+ * even more in the (far away) future
+ */
+QEMU_BUILD_BUG_ON(VIRTIO_FEATURES_NU32S != 4);
Another nitpick: there is a blank line after QEMU_BUILD_BUG_ON() in
"[RFC PATCH v4 05/14] virtio: serialize extended features state" but
this patch doesn't have a corresponding one. Please keep them consistent.
static const VMStateDescription vmstate_virtio_pci_modern_state_sub = {
.name = "virtio_pci/modern_state",
.version_id = 1,
@@ -124,11 +152,15 @@ static const VMStateDescription
vmstate_virtio_pci_modern_state_sub = {
.fields = (const VMStateField[]) {
VMSTATE_UINT32(dfselect, VirtIOPCIProxy),
VMSTATE_UINT32(gfselect, VirtIOPCIProxy),
- VMSTATE_UINT32_ARRAY(guest_features, VirtIOPCIProxy, 2),
+ VMSTATE_UINT32_SUB_ARRAY(guest_features, VirtIOPCIProxy, 0, 2),
VMSTATE_STRUCT_ARRAY(vqs, VirtIOPCIProxy, VIRTIO_QUEUE_MAX, 0,
vmstate_virtio_pci_modern_queue_state,
VirtIOPCIQueue),
VMSTATE_END_OF_LIST()
+ },
+ .subsections = (const VMStateDescription * const []) {
+ &vmstate_virtio_pci_modern_state_features128,
+ NULL
}
};
@@ -1477,6 +1509,13 @@ int virtio_pci_add_shm_cap(VirtIOPCIProxy *proxy,
return virtio_pci_add_mem_cap(proxy, &cap.cap);
}
+static int virtio_pci_select_max(const VirtIODevice *vdev)
+{
+ return virtio_features_use_ex(vdev->host_features_ex) ?
+ VIRTIO_FEATURES_NU32S :
+ 2;
This function could be simplified by replacing VIRTIO_FEATURES_NU32S
without any functional difference:
1. For writes: virtio_set_features_ex() already ignores extended
features when !virtio_features_use_ex(vdev->host_features_ex)
2. For reads: When !virtio_features_use_ex(vdev->host_features_ex), the
upper bits of host_features_ex are zero, and guest_features upper bits
remain zero (since they can't be set per point 1)
So the conditional logic is redundant here.
+}
+
static uint64_t virtio_pci_common_read(void *opaque, hwaddr addr,
unsigned size)
{
@@ -1494,18 +1533,21 @@ static uint64_t virtio_pci_common_read(void *opaque,
hwaddr addr,
val = proxy->dfselect;
break;
case VIRTIO_PCI_COMMON_DF:
- if (proxy->dfselect <= 1) {
+ if (proxy->dfselect < virtio_pci_select_max(vdev)) {
VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
- val = (vdev->host_features & ~vdc->legacy_features) >>
- (32 * proxy->dfselect);
+ val = vdev->host_features_ex[proxy->dfselect >> 1] >>
+ (32 * (proxy->dfselect & 1));
+ if (proxy->dfselect <= 1) {
+ val &= (~vdc->legacy_features) >> (32 * proxy->dfselect);
+ }
}
break;
case VIRTIO_PCI_COMMON_GFSELECT:
val = proxy->gfselect;
break;
case VIRTIO_PCI_COMMON_GF:
- if (proxy->gfselect < ARRAY_SIZE(proxy->guest_features)) {
+ if (proxy->gfselect < virtio_pci_select_max(vdev)) {
val = proxy->guest_features[proxy->gfselect];
}
break;
@@ -1588,11 +1630,18 @@ static void virtio_pci_common_write(void *opaque,
hwaddr addr,
proxy->gfselect = val;
break;
case VIRTIO_PCI_COMMON_GF:
- if (proxy->gfselect < ARRAY_SIZE(proxy->guest_features)) {
+ if (proxy->gfselect < virtio_pci_select_max(vdev)) {
+ uint64_t features[VIRTIO_FEATURES_NU64S];
+ int i;
+
proxy->guest_features[proxy->gfselect] = val;
- virtio_set_features(vdev,
- (((uint64_t)proxy->guest_features[1]) << 32) |
- proxy->guest_features[0]);
+ virtio_features_clear(features);
+ for (i = 0; i < ARRAY_SIZE(proxy->guest_features); ++i) {
+ uint64_t cur = proxy->guest_features[i];
+
+ features[i >> 1] |= cur << ((i & 1) * 32);
+ }
+ virtio_set_features_ex(vdev, features);
}
break;
case VIRTIO_PCI_COMMON_MSIX:
@@ -2311,6 +2360,8 @@ static void virtio_pci_reset(DeviceState *qdev)
virtio_bus_reset(bus);
msix_unuse_all_vectors(&proxy->pci_dev);
+ memset(proxy->guest_features, 0, sizeof(proxy->guest_features));
+
for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
proxy->vqs[i].enabled = 0;
proxy->vqs[i].reset = 0;
diff --git a/include/hw/virtio/virtio-pci.h b/include/hw/virtio/virtio-pci.h
index eab5394898..639752977e 100644
--- a/include/hw/virtio/virtio-pci.h
+++ b/include/hw/virtio/virtio-pci.h
@@ -158,7 +158,7 @@ struct VirtIOPCIProxy {
uint32_t nvectors;
uint32_t dfselect;
uint32_t gfselect;
- uint32_t guest_features[2];
+ uint32_t guest_features[VIRTIO_FEATURES_NU32S];
VirtIOPCIQueue vqs[VIRTIO_QUEUE_MAX];
VirtIOIRQFD *vector_irqfd;
