Add dma_translation attribute to iommu to enable/disable dma traslation
for intel-iommu

Signed-off-by: Sandesh Patel <sandesh.patel@nutanix.com>
---
 docs/formatdomain.rst             |  7 +++++++
 src/conf/domain_conf.c            | 15 +++++++++++++++
 src/conf/domain_conf.h            |  1 +
 src/conf/schemas/domaincommon.rng |  5 +++++
 4 files changed, 28 insertions(+)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index c56b739b23..a037ab65e4 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -8611,6 +8611,13 @@ Example:
       mapping larger iova addresses in the guest. :since:`Since 6.5.0` (QEMU/KVM
       only)
 
+   ``dma_translation``
+      The ``dma_translation`` attribute with possible values ``on`` and ``off`` can
+      be used to turn off the dma translation for IOMMU. It is useful when only
+      interrupt remapping is required but dma translation overhead is unwanted, for
+      example to efficiently enable more than 255 vCPUs.
+      :since:`Since 10.6.1` (QEMU/KVM only)
+
 The ``virtio`` IOMMU devices can further have ``address`` element as described
 in `Device addresses`_ (address has to by type of ``pci``).
 
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 86b563fbfb..d950921667 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -13931,6 +13931,10 @@ virDomainIOMMUDefParseXML(virDomainXMLOption *xmlopt,
         if (virXMLPropUInt(driver, "aw_bits", 10, VIR_XML_PROP_NONE,
                            &iommu->aw_bits) < 0)
             return NULL;
+
+        if (virXMLPropTristateSwitch(driver, "dma_translation", VIR_XML_PROP_NONE,
+                                     &iommu->dma_translation) < 0)
+            return NULL;
     }
 
     if (virDomainDeviceInfoParseXML(xmlopt, node, ctxt,
@@ -21467,6 +21471,13 @@ virDomainIOMMUDefCheckABIStability(virDomainIOMMUDef *src,
                        dst->aw_bits, src->aw_bits);
         return false;
     }
+    if (src->dma_translation != dst->dma_translation) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Target domain IOMMU device dma translation '%1$s' does not match source '%2$s'"),
+                       virTristateSwitchTypeToString(dst->dma_translation),
+                       virTristateSwitchTypeToString(src->dma_translation));
+        return false;
+    }
 
     return virDomainDeviceInfoCheckABIStability(&src->info, &dst->info);
 }
@@ -27451,6 +27462,10 @@ virDomainIOMMUDefFormat(virBuffer *buf,
         virBufferAsprintf(&driverAttrBuf, " aw_bits='%d'",
                           iommu->aw_bits);
     }
+    if (iommu->dma_translation != VIR_TRISTATE_SWITCH_ABSENT) {
+        virBufferAsprintf(&driverAttrBuf, " dma_translation='%s'",
+                          virTristateSwitchTypeToString(iommu->dma_translation));
+    }
 
     virXMLFormatElement(&childBuf, "driver", &driverAttrBuf, NULL);
 
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 95ddf5470e..eae621f900 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -2928,6 +2928,7 @@ struct _virDomainIOMMUDef {
     virTristateSwitch iotlb;
     unsigned int aw_bits;
     virDomainDeviceInfo info;
+    virTristateSwitch dma_translation;
 };
 
 typedef enum {
diff --git a/src/conf/schemas/domaincommon.rng b/src/conf/schemas/domaincommon.rng
index 7d58dce465..05ba697924 100644
--- a/src/conf/schemas/domaincommon.rng
+++ b/src/conf/schemas/domaincommon.rng
@@ -6100,6 +6100,11 @@
                 <ref name="uint8"/>
               </attribute>
             </optional>
+            <optional>
+              <attribute name="dma_translation">
+                <ref name="virOnOff"/>
+              </attribute>
+            </optional>
           </element>
         </optional>
         <optional>
-- 
2.22.3

On 8/7/24 09:37, Sandesh Patel wrote:
> Add dma_translation attribute to iommu to enable/disable dma traslation
> for intel-iommu
> 
> Signed-off-by: Sandesh Patel <sandesh.patel@nutanix.com>
> ---
>  docs/formatdomain.rst             |  7 +++++++
>  src/conf/domain_conf.c            | 15 +++++++++++++++
>  src/conf/domain_conf.h            |  1 +
>  src/conf/schemas/domaincommon.rng |  5 +++++
>  4 files changed, 28 insertions(+)
> 
> diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
> index c56b739b23..a037ab65e4 100644
> --- a/docs/formatdomain.rst
> +++ b/docs/formatdomain.rst
> @@ -8611,6 +8611,13 @@ Example:
>        mapping larger iova addresses in the guest. :since:`Since 6.5.0` (QEMU/KVM
>        only)
>  
> +   ``dma_translation``
> +      The ``dma_translation`` attribute with possible values ``on`` and ``off`` can
> +      be used to turn off the dma translation for IOMMU. It is useful when only
> +      interrupt remapping is required but dma translation overhead is unwanted, for
> +      example to efficiently enable more than 255 vCPUs.
> +      :since:`Since 10.6.1` (QEMU/KVM only)

This must be 10.7.0. The micro is reserved for maintenance releases
(which we don't really do anymore).

https://libvirt.org/downloads.html#release-numbering

Oh, and we often put xml2xml testcase here to prove parsing & formatting
works. This also drags in xml2cmd testcase, but that's okay. In fact, it
makes it more obvious how cmd line is changed once we start generating
it (patch 3/3).

Michal