[RFC HCI-8.1 PATCH 1/5] qemu update: allow qemu-update for VMs with PCI and USB hostdevs #VSTOR-103860 #VSTOR-137800

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

Previous commit 23ba7842b6 ("qemu update: disable update if hostdev
device is added to VM #VSTOR-97345") refused qemu-update for any domain
carrying a <hostdev>, because QEMU of that time could not preserve
passthrough devices across cpr-exec.  QEMU now does: VFIO devices
survive the update via the CPR FD preservation machinery, and USB
hostdevs are covered by QEMU as well.

Replace the blanket check with an allowlist.  PCI hostdevs (VFIO; this
also covers <interface type='hostdev'> SR-IOV VFs, which libvirt keeps
in the hostdevs array too) and USB hostdevs pass.  Other hostdev types
(mdev, scsi, scsi_host) haven't been validated with cpr-exec and are
still refused, now naming the offending type in the error.

NVMe disks (QEMU's userspace NVMe driver on top of VFIO) and vDPA
interfaces pin guest memory for device DMA just like VFIO devices, but
they are not hostdevs and thus never went through the hostdev check.
Refuse them explicitly, each with its own error.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 src/qemu/qemu_driver.c | 34 ++++++++++++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 911690e3909..b3902f10c65 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -25158,6 +25158,7 @@ qemuDomainGuestQemuUpdatePrechecks(virDomainObj *vm)
     qemuDomainObjPrivate *priv = vm->privateData;
     g_autoptr(GHashTable) blockjobstats = NULL;
     g_autoptr(virJSONValue) array = NULL;
+    size_t i;
 
     if (virDomainObjGetState(vm, NULL) != VIR_DOMAIN_RUNNING) {
         virReportError(VIR_ERR_OPERATION_INVALID,
@@ -25172,9 +25173,38 @@ qemuDomainGuestQemuUpdatePrechecks(virDomainObj *vm)
         return -1;
     }
 
-    if (vm->def->nhostdevs > 0) {
+    /* Only PCI (VFIO) and USB hostdevs are known to survive cpr-exec */
+    for (i = 0; i < vm->def->nhostdevs; i++) {
+        virDomainHostdevDef *hostdev = vm->def->hostdevs[i];
+        const char *type;
+
+        if (virHostdevIsPCIDevice(hostdev) ||
+            (hostdev->mode == VIR_DOMAIN_HOSTDEV_MODE_SUBSYS &&
+             hostdev->source.subsys.type == VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_USB))
+            continue;
+
+        if (hostdev->mode == VIR_DOMAIN_HOSTDEV_MODE_SUBSYS)
+            type = virDomainHostdevSubsysTypeToString(hostdev->source.subsys.type);
+        else
+            type = virDomainHostdevModeTypeToString(hostdev->mode);
+
         virReportError(VIR_ERR_OPERATION_INVALID,
-                       _("VM '%1$s' has hostdevs, qemu-update cancelled"), vm->def->name);
+                       _("VM '%1$s' has hostdev of unsupported type '%2$s', qemu-update cancelled"),
+                       vm->def->name, type);
+        return -1;
+    }
+
+    if (virDomainDefHasNVMeDisk(vm->def)) {
+        virReportError(VIR_ERR_OPERATION_INVALID,
+                       _("VM '%1$s' has NVMe disk, qemu-update cancelled"),
+                       vm->def->name);
+        return -1;
+    }
+
+    if (virDomainDefHasVDPANet(vm->def)) {
+        virReportError(VIR_ERR_OPERATION_INVALID,
+                       _("VM '%1$s' has vDPA interface, qemu-update cancelled"),
+                       vm->def->name);
         return -1;
     }
 
-- 
2.47.1