From 99ca73f9c43c7a266cf65f0012a5350197d0f229 Mon Sep 17 00:00:00 2001
Message-ID: <99ca73f9c43c7a266cf65f0012a5350197d0f229.1780571166.git.jdenemar@redhat.com>
From: Pavel Hrdina <phrdina@redhat.com>
Date: Fri, 13 Mar 2026 15:28:17 +0100
Subject: [PATCH] conf: Add iommufd fdgroup support

This will allow management applications running libvirt without
necessary permissions to pass FD for /dev/iommu with per-process
locked memory accounting enabled.

Kernel uses per-user locked memory accounting by default which may
cause error while starting multiple VMs with host devices using IOMMUFD.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
(cherry picked from commit 58875a6df679c5272f61028d33bf1380c51b0d5b)

Resolves: https://redhat.atlassian.net/browse/RHEL-156803
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
---
 docs/formatdomain.rst                  |  8 +++++++-
 src/conf/domain_conf.c                 |  6 ++++++
 src/conf/domain_conf.h                 |  1 +
 src/conf/domain_validate.c             | 16 ++++++++++++++++
 src/conf/schemas/domaincommon.rng      |  3 +++
 tests/genericxml2xmlindata/iommufd.xml |  2 +-
 6 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 86b3bad903..225152e0f2 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -1368,7 +1368,7 @@ Host Device IOMMUFD
 
    <domain>
      ...
-     <iommufd enabled='yes'/>
+     <iommufd enabled='yes' fdgroup='iommu'/>
      ...
    </domain>
 
@@ -1382,6 +1382,12 @@ Host Device IOMMUFD
    This controls IOMMUFD usage for all host devices, each device can change this
    global default by setting ``iommufd`` attribute for ``driver`` element.
 
+   Optional ``fdgroup`` attribute can be used together with
+   `virDomainFDAssociate <html/libvirt-libvirt-domain.html#virDomainFDAssociate>`__
+   to pass /dev/iommu FD instead of letting libvirt to open it. Caller is
+   responsible for setting per-process locked memory accounting otherwise
+   starting multiple VMs with host devices using IOMMUFD may fail.
+
 Resource partitioning
 ---------------------
 
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 1e91561fea..cec0f88f0f 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -4192,6 +4192,8 @@ void virDomainDefFree(virDomainDef *def)
     g_free(def->kvm_features);
     g_free(def->tcg_features);
 
+    g_free(def->iommufd_fdgroup);
+
     virBlkioDeviceArrayClear(def->blkio.devices,
                              def->blkio.ndevices);
     g_free(def->blkio.devices);
@@ -19765,6 +19767,8 @@ virDomainDefIommufdParse(virDomainDef *def,
     if (virXMLPropTristateBool(nodes[0], "enabled", VIR_XML_PROP_REQUIRED, &def->iommufd) < 0)
         return -1;
 
+    def->iommufd_fdgroup = virXMLPropString(nodes[0], "fdgroup");
+
     return 0;
 }
 
@@ -27998,6 +28002,8 @@ virDomainDefIommufdFormat(virBuffer *buf,
     virBufferAsprintf(&attrBuf, " enabled='%s'",
                       virTristateBoolTypeToString(def->iommufd));
 
+    virBufferEscapeString(&attrBuf, " fdgroup='%s'", def->iommufd_fdgroup);
+
     virXMLFormatElement(buf, "iommufd", &attrBuf, NULL);
 }
 
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index e12064a3ab..8c8c11c0cf 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -3232,6 +3232,7 @@ struct _virDomainDef {
     virDomainFeatureTCG *tcg_features;
 
     virTristateBool iommufd;
+    char *iommufd_fdgroup;
 
     bool tseg_specified;
     unsigned long long tseg_size;
diff --git a/src/conf/domain_validate.c b/src/conf/domain_validate.c
index 4558e7b210..3e6ba5e609 100644
--- a/src/conf/domain_validate.c
+++ b/src/conf/domain_validate.c
@@ -1995,6 +1995,19 @@ virDomainDefValidateThrottleGroups(const virDomainDef *def)
 }
 
 
+static int
+virDomainDefValidateIommufd(const virDomainDef *def)
+{
+    if (def->iommufd == VIR_TRISTATE_BOOL_NO && def->iommufd_fdgroup) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                       _("Setting 'fdgroup' when 'iommufd' is disabled is not supported."));
+        return -1;
+    }
+
+    return 0;
+}
+
+
 static int
 virDomainDefValidateInternal(const virDomainDef *def,
                              virDomainXMLOption *xmlopt)
@@ -2056,6 +2069,9 @@ virDomainDefValidateInternal(const virDomainDef *def,
     if (virDomainDefValidateThrottleGroups(def) < 0)
         return -1;
 
+    if (virDomainDefValidateIommufd(def) < 0)
+        return -1;
+
     return 0;
 }
 
diff --git a/src/conf/schemas/domaincommon.rng b/src/conf/schemas/domaincommon.rng
index 81b57a937a..9fde565d94 100644
--- a/src/conf/schemas/domaincommon.rng
+++ b/src/conf/schemas/domaincommon.rng
@@ -1353,6 +1353,9 @@
       <attribute name="enabled">
         <ref name="virYesNo"/>
       </attribute>
+      <optional>
+        <attribute name="fdgroup"/>
+      </optional>
     </element>
   </define>
 
diff --git a/tests/genericxml2xmlindata/iommufd.xml b/tests/genericxml2xmlindata/iommufd.xml
index 63ea839383..10d59ca548 100644
--- a/tests/genericxml2xmlindata/iommufd.xml
+++ b/tests/genericxml2xmlindata/iommufd.xml
@@ -4,7 +4,7 @@
   <memory unit='KiB'>219136</memory>
   <currentMemory unit='KiB'>219136</currentMemory>
   <vcpu placement='static'>1</vcpu>
-  <iommufd enabled='yes'/>
+  <iommufd enabled='yes' fdgroup='iommu'/>
   <os>
     <type arch='i686' machine='pc'>hvm</type>
     <boot dev='hd'/>
-- 
2.54.0