Re: [PATCH v3 2/3] qemu: add IOMMU attribute "cmdqv" for smmuv3

[Nathan Chen via Devel]

Hi Pavel,

On 8/18/2026 1:50 AM, Pavel Hrdina wrote:
On Tue, Aug 11, 2026 at 11:50:45AM -0700, Nathan Chen via Devel wrote:
From: Nathan Chen<nath...@nvidia.com>
Introduce support for "cmdqv" IOMMU attribute, which
enables NVIDIA Tegra241 CMDQV, an extension for ARM
SMMUv3. It supports passthroughs of physical SMMU-CMDQ
linked command queue from host space to a VM.

Signed-off-by: Nathan Chen<nath...@nvidia.com>
---
  docs/formatdomain.rst             |  6 ++++++
  src/conf/domain_conf.c            | 15 +++++++++++++++
  src/conf/domain_conf.h            |  1 +
  src/conf/domain_validate.c        |  6 +++++-
  src/conf/schemas/domaincommon.rng |  5 +++++
  src/qemu/qemu_command.c           |  1 +
  src/qemu/qemu_validate.c          |  1 -
  7 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 0b346a0952..2d5a34cb35 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -9436,6 +9436,12 @@ Examples:
        devices.
        :since:`Since 12.7.0` (QEMU/KVM and ``smmuv3`` model only)
  
+   ``cmdqv``
+      The ``cmdqv`` attribute with possible values ``on`` and ``off`` can be 
used
+      to enable NVIDIA Tegra241 CMDQV, an extension for ARM SMMUv3 that 
supports
+      passthrough of physical SMMU-CMDQ linked command queue from host space 
to VM.
+      :since:`Since 12.7.0` (QEMU/KVM and ``smmuv3`` model only)
+
It should mention the default value if accel is enabled like the other
attributes.

Right, I will include that line to match the other attributes.>> 
``ats``
        The ``ats`` attribute with possible values ``on`` and ``off`` can be
        used to enable reporting Address Translation Services capability to
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 9880339e42..42a0faca88 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -14758,6 +14758,10 @@ virDomainIOMMUDefParseXML(virDomainXMLOption *xmlopt,
                                       &iommu->accel) < 0)
              return NULL;
  
+        if (virXMLPropTristateSwitch(driver, "cmdqv", VIR_XML_PROP_NONE,
+                                     &iommu->cmdqv) < 0)
+            return NULL;
+
          if (virXMLPropTristateSwitch(driver, "ats", VIR_XML_PROP_NONE,
                                       &iommu->ats) < 0)
              return NULL;
@@ -16879,6 +16883,7 @@ virDomainIOMMUDefEquals(const virDomainIOMMUDef *a,
          a->dma_translation != b->dma_translation ||
          a->pci_bus != b->pci_bus ||
          a->accel != b->accel ||
+        a->cmdqv != b->cmdqv ||
          a->ats != b->ats ||
          a->ril != b->ril ||
          a->ssid_size != b->ssid_size ||
@@ -22773,6 +22778,12 @@ virDomainIOMMUDefCheckABIStability(virDomainIOMMUDef 
*src,
                         dst->accel, src->accel);
          return false;
      }
+    if (src->cmdqv != dst->cmdqv) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Target domain IOMMU device cmdqv value '%1$d' does not 
match source '%2$d'"),
+                       dst->cmdqv, src->cmdqv);
+        return false;
+    }
      if (src->ats != dst->ats) {
          virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
                         _("Target domain IOMMU device ATS value '%1$d' does not 
match source '%2$d'"),
@@ -29271,6 +29282,10 @@ virDomainIOMMUDefFormat(virBuffer *buf,
          virBufferAsprintf(&driverAttrBuf, " accel='%s'",
                            virTristateSwitchTypeToString(iommu->accel));
      }
+    if (iommu->cmdqv != VIR_TRISTATE_SWITCH_ABSENT) {
+            virBufferAsprintf(&driverAttrBuf, " cmdqv='%s'",
+                              virTristateSwitchTypeToString(iommu->cmdqv));
+        }
      if (iommu->ats != VIR_TRISTATE_SWITCH_ABSENT) {
          virBufferAsprintf(&driverAttrBuf, " ats='%s'",
                            virTristateSwitchTypeToString(iommu->ats));
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 2c017738e3..0c79bea015 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -3106,6 +3106,7 @@ struct _virDomainIOMMUDef {
      virTristateSwitch pt;
      int granule; /* -1 means 'host', 0 unset, page size in KiB otherwise */
      virTristateSwitch accel;
+    virTristateSwitch cmdqv;
      virTristateSwitch ats;
      virTristateSwitch ril;
      int ssid_size;
diff --git a/src/conf/domain_validate.c b/src/conf/domain_validate.c
index 710a891904..59b6c5f6d7 100644
--- a/src/conf/domain_validate.c
+++ b/src/conf/domain_validate.c
@@ -3207,7 +3207,8 @@ virDomainIOMMUDefValidate(const virDomainIOMMUDef *iommu)
              (iommu->ats != VIR_TRISTATE_SWITCH_ABSENT ||
               iommu->ril != VIR_TRISTATE_SWITCH_ABSENT ||
               iommu->ssid_size >= 0 ||
-             iommu->oas >= 0)) {
+             iommu->oas >= 0 ||
+             iommu->cmdqv != VIR_TRISTATE_SWITCH_ABSENT)) {
For consistency with the other conditions I would move the check between
accel and ats.

Otherwise looks good.
I will move this up in the next refresh.

Thanks,
Nathan