[PATCH 2/2] intel_iommu: Simplify caching mode check with VFIO device

[Zhenzhong Duan <zhenzhong.duan@intel.com>]

In early days, we have different tricks to ensure caching-mode=on with VFIO
device:

28cf553afe ("intel_iommu: Sanity check vfio-pci config on machine init done")
c6cbc29d36 ("pc/q35: Disallow vfio-pci hotplug without VT-d caching mode")
b8d78277c0 ("intel-iommu: fail MAP notifier without caching mode")

Because without caching mode, MAP notifier won't work correctly since guest
won't send IOTLB update event when it establishes new mappings in the I/O page
tables.

Now with host IOMMU device interface between VFIO and vIOMMU, we can simplify
it with a small check in set_iommu_device(). This also works for future VDPA
implementation which may also need caching mode on.

For coldplug VFIO device:

qemu-system-x86_64: -device vfio-pci,host=0000:3b:00.0,id=hostdev3,bus=root0,iommufd=iommufd0: vfio 0000:3b:00.0: Failed to set vIOMMU: Device assignment is not allowed without enabling caching-mode=on for Intel IOMMU.

For hotplug VFIO device:

Error: vfio 0000:3b:00.0: Failed to set vIOMMU: Device assignment is not allowed without enabling caching-mode=on for Intel IOMMU.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
---
 hw/i386/intel_iommu.c | 47 ++++++-------------------------------------
 hw/i386/pc.c          | 20 ------------------
 2 files changed, 6 insertions(+), 61 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index f04300022e..5c67b42dde 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -85,13 +85,6 @@ struct vtd_iotlb_key {
 static void vtd_address_space_refresh_all(IntelIOMMUState *s);
 static void vtd_address_space_unmap(VTDAddressSpace *as, IOMMUNotifier *n);
 
-static void vtd_panic_require_caching_mode(void)
-{
-    error_report("We need to set caching-mode=on for intel-iommu to enable "
-                 "device assignment with IOMMU protection.");
-    exit(1);
-}
-
 static void vtd_define_quad(IntelIOMMUState *s, hwaddr addr, uint64_t val,
                             uint64_t wmask, uint64_t w1cmask)
 {
@@ -3731,13 +3724,6 @@ static int vtd_iommu_notify_flag_changed(IOMMUMemoryRegion *iommu,
                          "Snoop Control with vhost or VFIO is not supported");
         return -ENOTSUP;
     }
-    if (!s->caching_mode && (new & IOMMU_NOTIFIER_MAP)) {
-        error_setg_errno(errp, ENOTSUP,
-                         "device %02x.%02x.%x requires caching mode",
-                         pci_bus_num(vtd_as->bus), PCI_SLOT(vtd_as->devfn),
-                         PCI_FUNC(vtd_as->devfn));
-        return -ENOTSUP;
-    }
     if (!x86_iommu->dt_supported && (new & IOMMU_NOTIFIER_DEVIOTLB_UNMAP)) {
         error_setg_errno(errp, ENOTSUP,
                          "device %02x.%02x.%x requires device IOTLB mode",
@@ -4378,6 +4364,12 @@ static bool vtd_dev_set_iommu_device(PCIBus *bus, void *opaque, int devfn,
 
     assert(hiod);
 
+    if (!s->caching_mode) {
+        error_setg(errp, "Device assignment is not allowed without enabling "
+                   "caching-mode=on for Intel IOMMU.");
+        return false;
+    }
+
     vtd_iommu_lock(s);
 
     if (g_hash_table_lookup(s->vtd_host_iommu_dev, &key)) {
@@ -4910,32 +4902,6 @@ static bool vtd_decide_config(IntelIOMMUState *s, Error **errp)
     return true;
 }
 
-static int vtd_machine_done_notify_one(Object *child, void *unused)
-{
-    IntelIOMMUState *iommu = INTEL_IOMMU_DEVICE(x86_iommu_get_default());
-
-    /*
-     * We hard-coded here because vfio-pci is the only special case
-     * here.  Let's be more elegant in the future when we can, but so
-     * far there seems to be no better way.
-     */
-    if (object_dynamic_cast(child, "vfio-pci") && !iommu->caching_mode) {
-        vtd_panic_require_caching_mode();
-    }
-
-    return 0;
-}
-
-static void vtd_machine_done_hook(Notifier *notifier, void *unused)
-{
-    object_child_foreach_recursive(object_get_root(),
-                                   vtd_machine_done_notify_one, NULL);
-}
-
-static Notifier vtd_machine_done_notify = {
-    .notify = vtd_machine_done_hook,
-};
-
 static void vtd_realize(DeviceState *dev, Error **errp)
 {
     MachineState *ms = MACHINE(qdev_get_machine());
@@ -4990,7 +4956,6 @@ static void vtd_realize(DeviceState *dev, Error **errp)
     pci_setup_iommu(bus, &vtd_iommu_ops, dev);
     /* Pseudo address space under root PCI bus. */
     x86ms->ioapic_as = vtd_host_dma_iommu(bus, s, Q35_PSEUDO_DEVFN_IOAPIC);
-    qemu_add_machine_init_done_notifier(&vtd_machine_done_notify);
 }
 
 static void vtd_class_init(ObjectClass *klass, const void *data)
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index bc048a6d13..01cd9a67db 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1720,25 +1720,6 @@ static void pc_machine_wakeup(MachineState *machine)
     cpu_synchronize_all_post_reset();
 }
 
-static bool pc_hotplug_allowed(MachineState *ms, DeviceState *dev, Error **errp)
-{
-    X86IOMMUState *iommu = x86_iommu_get_default();
-    IntelIOMMUState *intel_iommu;
-
-    if (iommu &&
-        object_dynamic_cast((Object *)iommu, TYPE_INTEL_IOMMU_DEVICE) &&
-        object_dynamic_cast((Object *)dev, "vfio-pci")) {
-        intel_iommu = INTEL_IOMMU_DEVICE(iommu);
-        if (!intel_iommu->caching_mode) {
-            error_setg(errp, "Device assignment is not allowed without "
-                       "enabling caching-mode=on for Intel IOMMU.");
-            return false;
-        }
-    }
-
-    return true;
-}
-
 static void pc_machine_class_init(ObjectClass *oc, const void *data)
 {
     MachineClass *mc = MACHINE_CLASS(oc);
@@ -1758,7 +1739,6 @@ static void pc_machine_class_init(ObjectClass *oc, const void *data)
     x86mc->apic_xrupt_override = true;
     assert(!mc->get_hotplug_handler);
     mc->get_hotplug_handler = pc_get_hotplug_handler;
-    mc->hotplug_allowed = pc_hotplug_allowed;
     mc->auto_enable_numa_with_memhp = true;
     mc->auto_enable_numa_with_memdev = true;
     mc->has_hotpluggable_cpus = true;
-- 
2.47.1