[v4] vEVENTQ support for accelerated SMMUv3 devices

[PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for accelerated SMMUv3 devices

Posted by Shameer Kolothum 5 days, 5 hours ago

From: Nicolin Chen <nicolinc@nvidia.com>

When the guest enables the Event Queue and a vIOMMU is present, allocate a
vEVENTQ object so that host-side events related to the vIOMMU can be
received and propagated back to the guest.

For cold-plugged devices using SMMUv3 acceleration, the vIOMMU is created
before the guest boots. In this case, the vEVENTQ is allocated when the
guest writes to SMMU_CR0 and sets EVENTQEN = 1.

If no cold-plugged device exists at boot (i.e. no vIOMMU initially), the
vEVENTQ is allocated when a vIOMMU is created, i.e. during the first
device hot-plug.

Event read and propagation will be added in a later patch.

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Tested-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
---
 hw/arm/smmuv3-accel.c | 61 +++++++++++++++++++++++++++++++++++++++++--
 hw/arm/smmuv3-accel.h |  6 +++++
 hw/arm/smmuv3.c       |  4 +++
 3 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
index c19c526fca..2ca0d1deac 100644
--- a/hw/arm/smmuv3-accel.c
+++ b/hw/arm/smmuv3-accel.c
@@ -390,6 +390,19 @@ bool smmuv3_accel_issue_inv_cmd(SMMUv3State *bs, void *cmd, SMMUDevice *sdev,
                    sizeof(Cmd), &entry_num, cmd, errp);
 }
 
+static void smmuv3_accel_free_veventq(SMMUv3AccelState *accel)
+{
+    IOMMUFDVeventq *veventq = accel->veventq;
+
+    if (!veventq) {
+        return;
+    }
+    close(veventq->veventq_fd);
+    iommufd_backend_free_id(accel->viommu->iommufd, veventq->veventq_id);
+    g_free(veventq);
+    accel->veventq = NULL;
+}
+
 static void smmuv3_accel_free_viommu(SMMUv3AccelState *accel)
 {
     IOMMUFDViommu *viommu = accel->viommu;
@@ -397,6 +410,7 @@ static void smmuv3_accel_free_viommu(SMMUv3AccelState *accel)
     if (!viommu) {
         return;
     }
+    smmuv3_accel_free_veventq(accel);
     iommufd_backend_free_id(viommu->iommufd, accel->bypass_hwpt_id);
     iommufd_backend_free_id(viommu->iommufd, accel->abort_hwpt_id);
     iommufd_backend_free_id(viommu->iommufd, accel->viommu->viommu_id);
@@ -404,6 +418,41 @@ static void smmuv3_accel_free_viommu(SMMUv3AccelState *accel)
     accel->viommu = NULL;
 }
 
+bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp)
+{
+    SMMUv3AccelState *accel = s->s_accel;
+    IOMMUFDVeventq *veventq;
+    uint32_t veventq_id;
+    uint32_t veventq_fd;
+
+    if (!accel->viommu) {
+        return true;
+    }
+
+    if (accel->veventq) {
+        return true;
+    }
+
+    if (!smmuv3_eventq_enabled(s)) {
+        return true;
+    }
+
+    if (!iommufd_backend_alloc_veventq(accel->viommu->iommufd,
+                                       accel->viommu->viommu_id,
+                                       IOMMU_VEVENTQ_TYPE_ARM_SMMUV3,
+                                       1 << s->eventq.log2size, &veventq_id,
+                                       &veventq_fd, errp)) {
+        return false;
+    }
+
+    veventq = g_new(IOMMUFDVeventq, 1);
+    veventq->veventq_id = veventq_id;
+    veventq->veventq_fd = veventq_fd;
+    veventq->viommu = accel->viommu;
+    accel->veventq = veventq;
+    return true;
+}
+
 static bool
 smmuv3_accel_alloc_viommu(SMMUv3State *s, HostIOMMUDeviceIOMMUFD *idev,
                           Error **errp)
@@ -429,6 +478,7 @@ smmuv3_accel_alloc_viommu(SMMUv3State *s, HostIOMMUDeviceIOMMUFD *idev,
     viommu->viommu_id = viommu_id;
     viommu->s2_hwpt_id = s2_hwpt_id;
     viommu->iommufd = idev->iommufd;
+    accel->viommu = viommu;
 
     /*
      * Pre-allocate HWPTs for S1 bypass and abort cases. These will be attached
@@ -448,14 +498,20 @@ smmuv3_accel_alloc_viommu(SMMUv3State *s, HostIOMMUDeviceIOMMUFD *idev,
         goto free_abort_hwpt;
     }
 
+    /* Allocate a vEVENTQ if guest has enabled event queue */
+    if (!smmuv3_accel_alloc_veventq(s, errp)) {
+        goto free_bypass_hwpt;
+    }
+
     /* Attach a HWPT based on SMMUv3 GBPA.ABORT value */
     hwpt_id = smmuv3_accel_gbpa_hwpt(s, accel);
     if (!host_iommu_device_iommufd_attach_hwpt(idev, hwpt_id, errp)) {
-        goto free_bypass_hwpt;
+        goto free_veventq;
     }
-    accel->viommu = viommu;
     return true;
 
+free_veventq:
+    smmuv3_accel_free_veventq(accel);
 free_bypass_hwpt:
     iommufd_backend_free_id(idev->iommufd, accel->bypass_hwpt_id);
 free_abort_hwpt:
@@ -463,6 +519,7 @@ free_abort_hwpt:
 free_viommu:
     iommufd_backend_free_id(idev->iommufd, viommu->viommu_id);
     g_free(viommu);
+    accel->viommu = NULL;
     return false;
 }
 
diff --git a/hw/arm/smmuv3-accel.h b/hw/arm/smmuv3-accel.h
index a8a64802ec..dba6c71de5 100644
--- a/hw/arm/smmuv3-accel.h
+++ b/hw/arm/smmuv3-accel.h
@@ -22,6 +22,7 @@
  */
 typedef struct SMMUv3AccelState {
     IOMMUFDViommu *viommu;
+    IOMMUFDVeventq *veventq;
     uint32_t bypass_hwpt_id;
     uint32_t abort_hwpt_id;
     QLIST_HEAD(, SMMUv3AccelDevice) device_list;
@@ -50,6 +51,7 @@ bool smmuv3_accel_attach_gbpa_hwpt(SMMUv3State *s, Error **errp);
 bool smmuv3_accel_issue_inv_cmd(SMMUv3State *s, void *cmd, SMMUDevice *sdev,
                                 Error **errp);
 void smmuv3_accel_idr_override(SMMUv3State *s);
+bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp);
 void smmuv3_accel_reset(SMMUv3State *s);
 #else
 static inline void smmuv3_accel_init(SMMUv3State *s)
@@ -80,6 +82,10 @@ smmuv3_accel_issue_inv_cmd(SMMUv3State *s, void *cmd, SMMUDevice *sdev,
 static inline void smmuv3_accel_idr_override(SMMUv3State *s)
 {
 }
+static inline bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp)
+{
+    return true;
+}
 static inline void smmuv3_accel_reset(SMMUv3State *s)
 {
 }
diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
index c08d58c579..210ac038fe 100644
--- a/hw/arm/smmuv3.c
+++ b/hw/arm/smmuv3.c
@@ -1605,6 +1605,10 @@ static MemTxResult smmu_writel(SMMUv3State *s, hwaddr offset,
         s->cr0ack = data & ~SMMU_CR0_RESERVED;
         /* in case the command queue has been enabled */
         smmuv3_cmdq_consume(s, &local_err);
+        /* Allocate vEVENTQ if EventQ is enabled and a vIOMMU is available */
+        if (local_err == NULL) {
+            smmuv3_accel_alloc_veventq(s, &local_err);
+        }
         break;
     case A_CR1:
         s->cr[1] = data;
-- 
2.43.0

Re: [PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for accelerated SMMUv3 devices

Posted by Eric Auger 4 days, 16 hours ago

Hi Shameer,

On 2/4/26 8:00 PM, Shameer Kolothum wrote:
> From: Nicolin Chen <nicolinc@nvidia.com>
>
> When the guest enables the Event Queue and a vIOMMU is present, allocate a
> vEVENTQ object so that host-side events related to the vIOMMU can be
> received and propagated back to the guest.
>
> For cold-plugged devices using SMMUv3 acceleration, the vIOMMU is created
> before the guest boots. In this case, the vEVENTQ is allocated when the
> guest writes to SMMU_CR0 and sets EVENTQEN = 1.
>
> If no cold-plugged device exists at boot (i.e. no vIOMMU initially), the
> vEVENTQ is allocated when a vIOMMU is created, i.e. during the first
> device hot-plug.
>
> Event read and propagation will be added in a later patch.
>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
> ---
>  hw/arm/smmuv3-accel.c | 61 +++++++++++++++++++++++++++++++++++++++++--
>  hw/arm/smmuv3-accel.h |  6 +++++
>  hw/arm/smmuv3.c       |  4 +++
>  3 files changed, 69 insertions(+), 2 deletions(-)
>
> diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
> index c19c526fca..2ca0d1deac 100644
> --- a/hw/arm/smmuv3-accel.c
> +++ b/hw/arm/smmuv3-accel.c
> @@ -390,6 +390,19 @@ bool smmuv3_accel_issue_inv_cmd(SMMUv3State *bs, void *cmd, SMMUDevice *sdev,
>                     sizeof(Cmd), &entry_num, cmd, errp);
>  }
>  
> +static void smmuv3_accel_free_veventq(SMMUv3AccelState *accel)
> +{
> +    IOMMUFDVeventq *veventq = accel->veventq;
> +
> +    if (!veventq) {
> +        return;
> +    }
> +    close(veventq->veventq_fd);
> +    iommufd_backend_free_id(accel->viommu->iommufd, veventq->veventq_id);
> +    g_free(veventq);
> +    accel->veventq = NULL;
> +}
> +
>  static void smmuv3_accel_free_viommu(SMMUv3AccelState *accel)
>  {
>      IOMMUFDViommu *viommu = accel->viommu;
> @@ -397,6 +410,7 @@ static void smmuv3_accel_free_viommu(SMMUv3AccelState *accel)
>      if (!viommu) {
>          return;
>      }
> +    smmuv3_accel_free_veventq(accel);
>      iommufd_backend_free_id(viommu->iommufd, accel->bypass_hwpt_id);
>      iommufd_backend_free_id(viommu->iommufd, accel->abort_hwpt_id);
>      iommufd_backend_free_id(viommu->iommufd, accel->viommu->viommu_id);
> @@ -404,6 +418,41 @@ static void smmuv3_accel_free_viommu(SMMUv3AccelState *accel)
>      accel->viommu = NULL;
>  }
>  
> +bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp)
> +{
> +    SMMUv3AccelState *accel = s->s_accel;
> +    IOMMUFDVeventq *veventq;
> +    uint32_t veventq_id;
> +    uint32_t veventq_fd;

you need to check !accel because in case of non accelerated SMMU it
sigsevs in smmu_writel/smmuv3_accel_alloc_veventq path

Thanks

Eric
>
> +
> +    if (!accel->viommu) {
> +        return true;
> +    }
> +
> +    if (accel->veventq) {
> +        return true;
> +    }
> +
> +    if (!smmuv3_eventq_enabled(s)) {
> +        return true;
> +    }
> +
> +    if (!iommufd_backend_alloc_veventq(accel->viommu->iommufd,
> +                                       accel->viommu->viommu_id,
> +                                       IOMMU_VEVENTQ_TYPE_ARM_SMMUV3,
> +                                       1 << s->eventq.log2size, &veventq_id,
> +                                       &veventq_fd, errp)) {
> +        return false;
> +    }
> +
> +    veventq = g_new(IOMMUFDVeventq, 1);
> +    veventq->veventq_id = veventq_id;
> +    veventq->veventq_fd = veventq_fd;
> +    veventq->viommu = accel->viommu;
> +    accel->veventq = veventq;
> +    return true;
> +}
> +
>  static bool
>  smmuv3_accel_alloc_viommu(SMMUv3State *s, HostIOMMUDeviceIOMMUFD *idev,
>                            Error **errp)
> @@ -429,6 +478,7 @@ smmuv3_accel_alloc_viommu(SMMUv3State *s, HostIOMMUDeviceIOMMUFD *idev,
>      viommu->viommu_id = viommu_id;
>      viommu->s2_hwpt_id = s2_hwpt_id;
>      viommu->iommufd = idev->iommufd;
> +    accel->viommu = viommu;
>  
>      /*
>       * Pre-allocate HWPTs for S1 bypass and abort cases. These will be attached
> @@ -448,14 +498,20 @@ smmuv3_accel_alloc_viommu(SMMUv3State *s, HostIOMMUDeviceIOMMUFD *idev,
>          goto free_abort_hwpt;
>      }
>  
> +    /* Allocate a vEVENTQ if guest has enabled event queue */
> +    if (!smmuv3_accel_alloc_veventq(s, errp)) {
> +        goto free_bypass_hwpt;
> +    }
> +
>      /* Attach a HWPT based on SMMUv3 GBPA.ABORT value */
>      hwpt_id = smmuv3_accel_gbpa_hwpt(s, accel);
>      if (!host_iommu_device_iommufd_attach_hwpt(idev, hwpt_id, errp)) {
> -        goto free_bypass_hwpt;
> +        goto free_veventq;
>      }
> -    accel->viommu = viommu;
>      return true;
>  
> +free_veventq:
> +    smmuv3_accel_free_veventq(accel);
>  free_bypass_hwpt:
>      iommufd_backend_free_id(idev->iommufd, accel->bypass_hwpt_id);
>  free_abort_hwpt:
> @@ -463,6 +519,7 @@ free_abort_hwpt:
>  free_viommu:
>      iommufd_backend_free_id(idev->iommufd, viommu->viommu_id);
>      g_free(viommu);
> +    accel->viommu = NULL;
>      return false;
>  }
>  
> diff --git a/hw/arm/smmuv3-accel.h b/hw/arm/smmuv3-accel.h
> index a8a64802ec..dba6c71de5 100644
> --- a/hw/arm/smmuv3-accel.h
> +++ b/hw/arm/smmuv3-accel.h
> @@ -22,6 +22,7 @@
>   */
>  typedef struct SMMUv3AccelState {
>      IOMMUFDViommu *viommu;
> +    IOMMUFDVeventq *veventq;
>      uint32_t bypass_hwpt_id;
>      uint32_t abort_hwpt_id;
>      QLIST_HEAD(, SMMUv3AccelDevice) device_list;
> @@ -50,6 +51,7 @@ bool smmuv3_accel_attach_gbpa_hwpt(SMMUv3State *s, Error **errp);
>  bool smmuv3_accel_issue_inv_cmd(SMMUv3State *s, void *cmd, SMMUDevice *sdev,
>                                  Error **errp);
>  void smmuv3_accel_idr_override(SMMUv3State *s);
> +bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp);
>  void smmuv3_accel_reset(SMMUv3State *s);
>  #else
>  static inline void smmuv3_accel_init(SMMUv3State *s)
> @@ -80,6 +82,10 @@ smmuv3_accel_issue_inv_cmd(SMMUv3State *s, void *cmd, SMMUDevice *sdev,
>  static inline void smmuv3_accel_idr_override(SMMUv3State *s)
>  {
>  }
> +static inline bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp)
> +{
> +    return true;
> +}
>  static inline void smmuv3_accel_reset(SMMUv3State *s)
>  {
>  }
> diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
> index c08d58c579..210ac038fe 100644
> --- a/hw/arm/smmuv3.c
> +++ b/hw/arm/smmuv3.c
> @@ -1605,6 +1605,10 @@ static MemTxResult smmu_writel(SMMUv3State *s, hwaddr offset,
>          s->cr0ack = data & ~SMMU_CR0_RESERVED;
>          /* in case the command queue has been enabled */
>          smmuv3_cmdq_consume(s, &local_err);
> +        /* Allocate vEVENTQ if EventQ is enabled and a vIOMMU is available */
> +        if (local_err == NULL) {
> +            smmuv3_accel_alloc_veventq(s, &local_err);
> +        }
>          break;
>      case A_CR1:
>          s->cr[1] = data;

RE: [PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for accelerated SMMUv3 devices

Posted by Shameer Kolothum Thodi 4 days, 15 hours ago


> -----Original Message-----
> From: Eric Auger <eric.auger@redhat.com>
> Sent: 05 February 2026 08:33
> To: Shameer Kolothum Thodi <skolothumtho@nvidia.com>; qemu-
> arm@nongnu.org; qemu-devel@nongnu.org
> Cc: peter.maydell@linaro.org; Nicolin Chen <nicolinc@nvidia.com>; Nathan
> Chen <nathanc@nvidia.com>; Matt Ochs <mochs@nvidia.com>; Jason
> Gunthorpe <jgg@nvidia.com>; jonathan.cameron@huawei.com;
> zhangfei.gao@linaro.org; zhenzhong.duan@intel.com; Krishnakant Jaju
> <kjaju@nvidia.com>
> Subject: Re: [PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for
> accelerated SMMUv3 devices
> 
> External email: Use caution opening links or attachments
> 
> 
> Hi Shameer,
> 
> On 2/4/26 8:00 PM, Shameer Kolothum wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> >
> > When the guest enables the Event Queue and a vIOMMU is present, allocate
> a
> > vEVENTQ object so that host-side events related to the vIOMMU can be
> > received and propagated back to the guest.
> >
> > For cold-plugged devices using SMMUv3 acceleration, the vIOMMU is
> created
> > before the guest boots. In this case, the vEVENTQ is allocated when the
> > guest writes to SMMU_CR0 and sets EVENTQEN = 1.
> >
> > If no cold-plugged device exists at boot (i.e. no vIOMMU initially), the
> > vEVENTQ is allocated when a vIOMMU is created, i.e. during the first
> > device hot-plug.
> >
> > Event read and propagation will be added in a later patch.
> >
> > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> > Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> > Reviewed-by: Eric Auger <eric.auger@redhat.com>
> > Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
> > ---
> >  hw/arm/smmuv3-accel.c | 61
> +++++++++++++++++++++++++++++++++++++++++--
> >  hw/arm/smmuv3-accel.h |  6 +++++
> >  hw/arm/smmuv3.c       |  4 +++
> >  3 files changed, 69 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
> > index c19c526fca..2ca0d1deac 100644
> > --- a/hw/arm/smmuv3-accel.c
> > +++ b/hw/arm/smmuv3-accel.c
> > @@ -390,6 +390,19 @@ bool
> smmuv3_accel_issue_inv_cmd(SMMUv3State *bs, void *cmd, SMMUDevice
> *sdev,
> >                     sizeof(Cmd), &entry_num, cmd, errp);
> >  }
> >
> > +static void smmuv3_accel_free_veventq(SMMUv3AccelState *accel)
> > +{
> > +    IOMMUFDVeventq *veventq = accel->veventq;
> > +
> > +    if (!veventq) {
> > +        return;
> > +    }
> > +    close(veventq->veventq_fd);
> > +    iommufd_backend_free_id(accel->viommu->iommufd, veventq-
> >veventq_id);
> > +    g_free(veventq);
> > +    accel->veventq = NULL;
> > +}
> > +
> >  static void smmuv3_accel_free_viommu(SMMUv3AccelState *accel)
> >  {
> >      IOMMUFDViommu *viommu = accel->viommu;
> > @@ -397,6 +410,7 @@ static void
> smmuv3_accel_free_viommu(SMMUv3AccelState *accel)
> >      if (!viommu) {
> >          return;
> >      }
> > +    smmuv3_accel_free_veventq(accel);
> >      iommufd_backend_free_id(viommu->iommufd, accel->bypass_hwpt_id);
> >      iommufd_backend_free_id(viommu->iommufd, accel->abort_hwpt_id);
> >      iommufd_backend_free_id(viommu->iommufd, accel->viommu-
> >viommu_id);
> > @@ -404,6 +418,41 @@ static void
> smmuv3_accel_free_viommu(SMMUv3AccelState *accel)
> >      accel->viommu = NULL;
> >  }
> >
> > +bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp)
> > +{
> > +    SMMUv3AccelState *accel = s->s_accel;
> > +    IOMMUFDVeventq *veventq;
> > +    uint32_t veventq_id;
> > +    uint32_t veventq_fd;
> 
> you need to check !accel because in case of non accelerated SMMU it
> sigsevs in smmu_writel/smmuv3_accel_alloc_veventq path

Oops. Right. Will add.

Thanks,
Shameer

Re: [PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for accelerated SMMUv3 devices

Posted by Nicolin Chen 5 days, 4 hours ago

On Wed, Feb 04, 2026 at 07:00:06PM +0000, Shameer Kolothum wrote:
> +bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp)
> +{
> +    SMMUv3AccelState *accel = s->s_accel;
> +    IOMMUFDVeventq *veventq;
> +    uint32_t veventq_id;
> +    uint32_t veventq_fd;
> +
> +    if (!accel->viommu) {
> +        return true;
> +    }

This seems meaningless or should be an assert?

Other looks okay.

Nicolin

RE: [PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for accelerated SMMUv3 devices

Posted by Shameer Kolothum Thodi 4 days, 16 hours ago


> -----Original Message-----
> From: Nicolin Chen <nicolinc@nvidia.com>
> Sent: 04 February 2026 19:55
> To: Shameer Kolothum Thodi <skolothumtho@nvidia.com>
> Cc: qemu-arm@nongnu.org; qemu-devel@nongnu.org;
> eric.auger@redhat.com; peter.maydell@linaro.org; Nathan Chen
> <nathanc@nvidia.com>; Matt Ochs <mochs@nvidia.com>; Jason Gunthorpe
> <jgg@nvidia.com>; jonathan.cameron@huawei.com;
> zhangfei.gao@linaro.org; zhenzhong.duan@intel.com; Krishnakant Jaju
> <kjaju@nvidia.com>
> Subject: Re: [PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for
> accelerated SMMUv3 devices
> 
> On Wed, Feb 04, 2026 at 07:00:06PM +0000, Shameer Kolothum wrote:
> > +bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp) {
> > +    SMMUv3AccelState *accel = s->s_accel;
> > +    IOMMUFDVeventq *veventq;
> > +    uint32_t veventq_id;
> > +    uint32_t veventq_fd;
> > +
> > +    if (!accel->viommu) {
> > +        return true;
> > +    }
> 
> This seems meaningless or should be an assert?

Hmm.. We need this check because, if there are no cold-plugged devices,
when the guest boots and enables EventQ, the vIOMMU may not exist yet.

Isn't it?

Thanks,
Shameer

Re: [PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for accelerated SMMUv3 devices

Posted by Nicolin Chen 4 days, 8 hours ago

On Thu, Feb 05, 2026 at 12:26:40AM -0800, Shameer Kolothum Thodi wrote:
> 
> 
> > -----Original Message-----
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: 04 February 2026 19:55
> > To: Shameer Kolothum Thodi <skolothumtho@nvidia.com>
> > Cc: qemu-arm@nongnu.org; qemu-devel@nongnu.org;
> > eric.auger@redhat.com; peter.maydell@linaro.org; Nathan Chen
> > <nathanc@nvidia.com>; Matt Ochs <mochs@nvidia.com>; Jason Gunthorpe
> > <jgg@nvidia.com>; jonathan.cameron@huawei.com;
> > zhangfei.gao@linaro.org; zhenzhong.duan@intel.com; Krishnakant Jaju
> > <kjaju@nvidia.com>
> > Subject: Re: [PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for
> > accelerated SMMUv3 devices
> > 
> > On Wed, Feb 04, 2026 at 07:00:06PM +0000, Shameer Kolothum wrote:
> > > +bool smmuv3_accel_alloc_veventq(SMMUv3State *s, Error **errp) {
> > > +    SMMUv3AccelState *accel = s->s_accel;
> > > +    IOMMUFDVeventq *veventq;
> > > +    uint32_t veventq_id;
> > > +    uint32_t veventq_fd;
> > > +
> > > +    if (!accel->viommu) {
> > > +        return true;
> > > +    }
> > 
> > This seems meaningless or should be an assert?
> 
> Hmm.. We need this check because, if there are no cold-plugged devices,
> when the guest boots and enables EventQ, the vIOMMU may not exist yet.
> 
> Isn't it?

Oh, you are right. I missed the other call in smmu_writel().

Nicolin

[PATCH v4 1/5] backends/iommufd: Introduce iommufd_backend_alloc_veventq
[PATCH v4 2/5] hw/arm/smmuv3-accel: Add viommu free helper
[PATCH v4 3/5] hw/arm/smmuv3-accel: Allocate vEVENTQ for accelerated SMMUv3 devices
[PATCH v4 4/5] hw/arm/smmuv3: Introduce a helper function for event propagation
[PATCH v4 5/5] hw/arm/smmuv3-accel: Read and propagate host vIOMMU events