From 844d1036eb734b6c80397a0c69f491645c682313 Mon Sep 17 00:00:00 2001
From: Michal Privoznik <mprivozn@redhat.com>
Date: Wed, 6 Nov 2024 12:57:21 +0100
Subject: [PATCH] qemu_domain: Automagically add IOMMU if needed
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If a Q35 domain has huge number of vCPUS (over 255, currently), then
it needs IOMMU with Extended Interrupt Mode enabled (see check in
qemuValidateDomainVCpuTopology()).

Well, we already add some devices and to other tricks when
parsing new domain XML. Might as well add IOMMU device if above
condition is met.

Resolves: https://issues.redhat.com/browse/RHEL-65844
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
---
 src/qemu/qemu_domain.c                        | 20 +++++++++++++++++++
 .../intel-iommu-eim-autoadd.xml               |  1 -
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 39f3e38351..562fa76a78 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -4262,6 +4262,7 @@ qemuDomainDefAddDefaultDevices(virQEMUDriver *driver,
     bool addDefaultUSBMouse = false;
     bool addPanicDevice = false;
     bool addITCOWatchdog = false;
+    bool addIOMMU = false;
 
     /* add implicit input devices */
     if (qemuDomainDefAddImplicitInputDevice(def, qemuCaps) < 0)
@@ -4284,6 +4285,10 @@ qemuDomainDefAddDefaultDevices(virQEMUDriver *driver,
             addImplicitSATA = true;
             addITCOWatchdog = true;
 
+            if (virDomainDefGetVcpusMax(def) > QEMU_MAX_VCPUS_WITHOUT_EIM) {
+                addIOMMU = true;
+            }
+
             /* Prefer adding a USB3 controller if supported, fall back
              * to USB2 if there is no USB3 available, and if that's
              * unavailable don't add anything.
@@ -4530,6 +4535,21 @@ qemuDomainDefAddDefaultDevices(virQEMUDriver *driver,
         }
     }
 
+    if (addIOMMU && !def->iommu &&
+        virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_INTEL_IOMMU) &&
+        virQEMUCapsGet(qemuCaps, QEMU_CAPS_INTEL_IOMMU_INTREMAP) &&
+        virQEMUCapsGet(qemuCaps, QEMU_CAPS_INTEL_IOMMU_EIM)) {
+        g_autoptr(virDomainIOMMUDef) iommu = NULL;
+
+        iommu = virDomainIOMMUDefNew();
+        iommu->model = VIR_DOMAIN_IOMMU_MODEL_INTEL;
+        /* eim requires intremap. */
+        iommu->intremap = VIR_TRISTATE_SWITCH_ON;
+        iommu->eim = VIR_TRISTATE_SWITCH_ON;
+
+        def->iommu = g_steal_pointer(&iommu);
+    }
+
     if (qemuDomainDefAddDefaultAudioBackend(driver, def) < 0)
         return -1;
 
diff --git a/tests/qemuxmlconfdata/intel-iommu-eim-autoadd.xml b/tests/qemuxmlconfdata/intel-iommu-eim-autoadd.xml
index 7c294fe2f9..fa3aaf0d44 100644
--- a/tests/qemuxmlconfdata/intel-iommu-eim-autoadd.xml
+++ b/tests/qemuxmlconfdata/intel-iommu-eim-autoadd.xml
@@ -30,6 +30,5 @@
     <audio id='1' type='none'/>
     <watchdog model='itco' action='reset'/>
     <memballoon model='none'/>
-    <iommu model='intel'/>
   </devices>
 </domain>