From: Rahul Singh <rahul.singh@arm.com>

This patch adds basic framework for vIOMMU.

Signed-off-by: Rahul Singh <rahul.singh@arm.com>
Signed-off-by: Milan Djokic <milan_djokic@epam.com>
---
 xen/arch/arm/dom0less-build.c        |  2 +
 xen/arch/arm/domain.c                | 25 ++++++++++
 xen/arch/arm/domain_build.c          |  2 +
 xen/arch/arm/include/asm/viommu.h    | 70 ++++++++++++++++++++++++++++
 xen/drivers/passthrough/Kconfig      |  5 ++
 xen/drivers/passthrough/arm/Makefile |  1 +
 xen/drivers/passthrough/arm/viommu.c | 48 +++++++++++++++++++
 xen/include/public/arch-arm.h        |  4 ++
 8 files changed, 157 insertions(+)
 create mode 100644 xen/arch/arm/include/asm/viommu.h
 create mode 100644 xen/drivers/passthrough/arm/viommu.c

diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
index 4181c10538..067835e5d0 100644
--- a/xen/arch/arm/dom0less-build.c
+++ b/xen/arch/arm/dom0less-build.c
@@ -23,6 +23,7 @@
 #include <asm/arm64/sve.h>
 #include <asm/domain_build.h>
 #include <asm/firmware/sci.h>
+#include <asm/viommu.h>
 #include <asm/grant_table.h>
 #include <asm/setup.h>
 
@@ -317,6 +318,7 @@ int __init arch_parse_dom0less_node(struct dt_device_node *node,
     uint32_t val;
 
     d_cfg->arch.gic_version = XEN_DOMCTL_CONFIG_GIC_NATIVE;
+    d_cfg->arch.viommu_type = viommu_get_type();
     d_cfg->flags |= XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap;
 
     if ( domu_dt_sci_parse(node, d_cfg) )
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 94b9858ad2..37511c9323 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -28,6 +28,7 @@
 #include <asm/tee/tee.h>
 #include <asm/vfp.h>
 #include <asm/vgic.h>
+#include <asm/viommu.h>
 #include <asm/vtimer.h>
 
 #include "vpci.h"
@@ -626,6 +627,21 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
         return -EINVAL;
     }
 
+    if ( !(config->flags & XEN_DOMCTL_CDF_iommu) &&
+         config->arch.viommu_type != XEN_DOMCTL_CONFIG_VIOMMU_NONE )
+    {
+        dprintk(XENLOG_INFO,
+                "vIOMMU requested while iommu not enabled for domain\n");
+        return -EINVAL;
+    }
+
+    if ( config->arch.viommu_type != XEN_DOMCTL_CONFIG_VIOMMU_NONE )
+    {
+        dprintk(XENLOG_INFO,
+                "vIOMMU type requested not supported by the platform or Xen\n");
+        return -EINVAL;
+    }
+
     return sci_domain_sanitise_config(config);
 }
 
@@ -721,6 +737,9 @@ int arch_domain_create(struct domain *d,
     if ( (rc = sci_domain_init(d, config)) != 0 )
         goto fail;
 
+    if ( (rc = domain_viommu_init(d, config->arch.viommu_type)) != 0 )
+        goto fail;
+
     return 0;
 
 fail:
@@ -965,6 +984,7 @@ enum {
     PROG_pci = 1,
     PROG_sci,
     PROG_tee,
+    PROG_viommu,
     PROG_xen,
     PROG_page,
     PROG_mapping,
@@ -1021,6 +1041,11 @@ int domain_relinquish_resources(struct domain *d)
         if (ret )
             return ret;
 
+    PROGRESS(viommu):
+        ret = viommu_relinquish_resources(d);
+        if (ret )
+            return ret;
+
     PROGRESS(xen):
         ret = relinquish_memory(d, &d->xenpage_list);
         if ( ret )
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index e8795745dd..a51563ee3d 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -35,6 +35,7 @@
 #include <asm/arm64/sve.h>
 #include <asm/cpufeature.h>
 #include <asm/domain_build.h>
+#include <asm/viommu.h>
 #include <xen/event.h>
 
 #include <xen/irq.h>
@@ -1946,6 +1947,7 @@ void __init create_dom0(void)
     dom0_cfg.arch.nr_spis = vgic_def_nr_spis();
     dom0_cfg.arch.tee_type = tee_get_type();
     dom0_cfg.max_vcpus = dom0_max_vcpus();
+    dom0_cfg.arch.viommu_type = viommu_get_type();
 
     if ( iommu_enabled )
         dom0_cfg.flags |= XEN_DOMCTL_CDF_iommu;
diff --git a/xen/arch/arm/include/asm/viommu.h b/xen/arch/arm/include/asm/viommu.h
new file mode 100644
index 0000000000..7cd3818a12
--- /dev/null
+++ b/xen/arch/arm/include/asm/viommu.h
@@ -0,0 +1,70 @@
+/* SPDX-License-Identifier: (GPL-2.0-or-later OR BSD-2-Clause) */
+#ifndef __ARCH_ARM_VIOMMU_H__
+#define __ARCH_ARM_VIOMMU_H__
+
+#ifdef CONFIG_VIRTUAL_IOMMU
+
+#include <xen/lib.h>
+#include <xen/types.h>
+#include <public/xen.h>
+
+struct viommu_ops {
+    /*
+     * Called during domain construction if toolstack requests to enable
+     * vIOMMU support.
+     */
+    int (*domain_init)(struct domain *d);
+
+    /*
+     * Called during domain destruction to free resources used by vIOMMU.
+     */
+    int (*relinquish_resources)(struct domain *d);
+};
+
+struct viommu_desc {
+    /* vIOMMU domains init/free operations described above. */
+    const struct viommu_ops *ops;
+
+    /*
+     * ID of vIOMMU. Corresponds to xen_arch_domainconfig.viommu_type.
+     * Should be one of XEN_DOMCTL_CONFIG_VIOMMU_xxx
+     */
+    uint16_t viommu_type;
+};
+
+int domain_viommu_init(struct domain *d, uint16_t viommu_type);
+int viommu_relinquish_resources(struct domain *d);
+uint16_t viommu_get_type(void);
+
+#else
+
+static inline uint8_t viommu_get_type(void)
+{
+    return XEN_DOMCTL_CONFIG_VIOMMU_NONE;
+}
+
+static inline int domain_viommu_init(struct domain *d, uint16_t viommu_type)
+{
+    if ( likely(viommu_type == XEN_DOMCTL_CONFIG_VIOMMU_NONE) )
+        return 0;
+
+    return -ENODEV;
+}
+
+static inline int viommu_relinquish_resources(struct domain *d)
+{
+    return 0;
+}
+
+#endif /* CONFIG_VIRTUAL_IOMMU */
+
+#endif /* __ARCH_ARM_VIOMMU_H__ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/drivers/passthrough/Kconfig b/xen/drivers/passthrough/Kconfig
index b413c33a4c..487331607c 100644
--- a/xen/drivers/passthrough/Kconfig
+++ b/xen/drivers/passthrough/Kconfig
@@ -35,6 +35,11 @@ config IPMMU_VMSA
 	  (H3 ES3.0, M3-W+, etc) or Gen4 SoCs which IPMMU hardware supports stage 2
 	  translation table format and is able to use CPU's P2M table as is.
 
+config VIRTUAL_IOMMU
+	bool "Virtual IOMMU Support (UNSUPPORTED)" if UNSUPPORTED
+	help
+	 Support virtual IOMMU infrastructure to implement vIOMMU.
+
 endif
 
 config AMD_IOMMU
diff --git a/xen/drivers/passthrough/arm/Makefile b/xen/drivers/passthrough/arm/Makefile
index c5fb3b58a5..4cc54f3f4d 100644
--- a/xen/drivers/passthrough/arm/Makefile
+++ b/xen/drivers/passthrough/arm/Makefile
@@ -2,3 +2,4 @@ obj-y += iommu.o iommu_helpers.o iommu_fwspec.o
 obj-$(CONFIG_ARM_SMMU) += smmu.o
 obj-$(CONFIG_IPMMU_VMSA) += ipmmu-vmsa.o
 obj-$(CONFIG_ARM_SMMU_V3) += smmu-v3.o
+obj-$(CONFIG_VIRTUAL_IOMMU) += viommu.o
diff --git a/xen/drivers/passthrough/arm/viommu.c b/xen/drivers/passthrough/arm/viommu.c
new file mode 100644
index 0000000000..7ab6061e34
--- /dev/null
+++ b/xen/drivers/passthrough/arm/viommu.c
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: (GPL-2.0-or-later OR BSD-2-Clause) */
+
+#include <xen/errno.h>
+#include <xen/init.h>
+#include <xen/types.h>
+
+#include <asm/viommu.h>
+
+const struct viommu_desc __read_mostly *cur_viommu;
+
+int domain_viommu_init(struct domain *d, uint16_t viommu_type)
+{
+    if ( viommu_type == XEN_DOMCTL_CONFIG_VIOMMU_NONE )
+        return 0;
+
+    if ( !cur_viommu )
+        return -ENODEV;
+
+    if ( cur_viommu->viommu_type != viommu_type )
+        return -EINVAL;
+
+    return cur_viommu->ops->domain_init(d);
+}
+
+int viommu_relinquish_resources(struct domain *d)
+{
+    if ( !cur_viommu )
+        return 0;
+
+    return cur_viommu->ops->relinquish_resources(d);
+}
+
+uint16_t viommu_get_type(void)
+{
+    if ( !cur_viommu )
+        return XEN_DOMCTL_CONFIG_VIOMMU_NONE;
+
+    return cur_viommu->viommu_type;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index cd563cf706..b1db2bf19d 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -330,12 +330,16 @@ DEFINE_XEN_GUEST_HANDLE(vcpu_guest_context_t);
 #define XEN_DOMCTL_CONFIG_ARM_SCI_NONE      0
 #define XEN_DOMCTL_CONFIG_ARM_SCI_SCMI_SMC  1
 
+#define XEN_DOMCTL_CONFIG_VIOMMU_NONE   0
+
 struct xen_arch_domainconfig {
     /* IN/OUT */
     uint8_t gic_version;
     /* IN - Contains SVE vector length divided by 128 */
     uint8_t sve_vl;
     /* IN */
+    uint8_t viommu_type;
+    /* IN */
     uint16_t tee_type;
     /* IN */
     uint32_t nr_spis;
-- 
2.43.0

On 23.03.2026 23:51, Milan Djokic wrote:
> --- a/xen/include/public/arch-arm.h
> +++ b/xen/include/public/arch-arm.h
> @@ -330,12 +330,16 @@ DEFINE_XEN_GUEST_HANDLE(vcpu_guest_context_t);
>  #define XEN_DOMCTL_CONFIG_ARM_SCI_NONE      0
>  #define XEN_DOMCTL_CONFIG_ARM_SCI_SCMI_SMC  1
>  
> +#define XEN_DOMCTL_CONFIG_VIOMMU_NONE   0
> +
>  struct xen_arch_domainconfig {
>      /* IN/OUT */
>      uint8_t gic_version;
>      /* IN - Contains SVE vector length divided by 128 */
>      uint8_t sve_vl;
>      /* IN */
> +    uint8_t viommu_type;
> +    /* IN */
>      uint16_t tee_type;
>      /* IN */
>      uint32_t nr_spis;

You're altering structure layout, and hence an interface version change is
needed. Adding at the end would be less intrusive (no real change to layout),
but still would require an interface version bump due to the lack of
checking that the 3 padding bytes are actually 0. (IOW to help future
changes, you may want to add explicit padding bytes along with the new field
you need, and check them to be zero.)

Jan

On 23.03.2026 23:51, Milan Djokic wrote:
> --- a/xen/drivers/passthrough/Kconfig
> +++ b/xen/drivers/passthrough/Kconfig
> @@ -35,6 +35,11 @@ config IPMMU_VMSA
>  	  (H3 ES3.0, M3-W+, etc) or Gen4 SoCs which IPMMU hardware supports stage 2
>  	  translation table format and is able to use CPU's P2M table as is.
>  
> +config VIRTUAL_IOMMU
> +	bool "Virtual IOMMU Support (UNSUPPORTED)" if UNSUPPORTED
> +	help
> +	 Support virtual IOMMU infrastructure to implement vIOMMU.
> +
>  endif

This is being added to an Arm-only section, without it having an Arm-only
name. Judging from the diffstat in the cover letter, there's hardly any
abstraction in common code, so likely adding an ARM_ prefix to the name
would be the way to go (for now, i.e. if doing proper abstraction is
specifically not a goal).

Jan

Hello Jan,

On 3/24/26 09:27, Jan Beulich wrote:
> On 23.03.2026 23:51, Milan Djokic wrote:
>> --- a/xen/drivers/passthrough/Kconfig
>> +++ b/xen/drivers/passthrough/Kconfig
>> @@ -35,6 +35,11 @@ config IPMMU_VMSA
>>   	  (H3 ES3.0, M3-W+, etc) or Gen4 SoCs which IPMMU hardware supports stage 2
>>   	  translation table format and is able to use CPU's P2M table as is.
>>   
>> +config VIRTUAL_IOMMU
>> +	bool "Virtual IOMMU Support (UNSUPPORTED)" if UNSUPPORTED
>> +	help
>> +	 Support virtual IOMMU infrastructure to implement vIOMMU.
>> +
>>   endif
> 
> This is being added to an Arm-only section, without it having an Arm-only
> name. Judging from the diffstat in the cover letter, there's hardly any
> abstraction in common code, so likely adding an ARM_ prefix to the name
> would be the way to go (for now, i.e. if doing proper abstraction is
> specifically not a goal).
> 
> Jan

The idea is to reuse (if possible) the generic framework covered by this 
configuration option for RISC-V in the future. At the moment, most of 
the implementation resides under the ARM section, since only SMMUv3 
hardware is supported. I will add the ARM prefix for now and update the 
other patches according to the review comments.

BR,
Milan