Re: [PATCH RFCv1 03/10] hw/arm/virt: Get the number of host-level SMMUv3 instances

[Eric Auger]

Hi Nicolin,

On 6/26/24 02:28, Nicolin Chen wrote:
> Nested SMMUv3 feature requires the support/presence of host-level SMMUv3
> instance(s). Add a helper to read the sysfs for the number of instances.
> Log them in a vms list using a new struct VirtNestedSmmu.
>
> This will be used by a following patch to assign a passthrough device to
> corresponding nested SMMUv3 instance.
Laterly the HostIOMMUDevice has been introduced to allow, among other
things, to pass information related to the physical IOMMU to the virtual
IOMMU.
I guess it would be well fitted to associate the viommu with its
underlying piommu.

I don't think we have such kind of host introspection in machine type.
Generally in can happen in the very device or in libvirt.

Thanks

Eric
>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>  hw/arm/virt.c         | 35 +++++++++++++++++++++++++++++++++++
>  include/hw/arm/virt.h |  8 ++++++++
>  2 files changed, 43 insertions(+)
>
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 71093d7c60..be3d8b0ce6 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -2668,6 +2668,37 @@ static char *virt_get_iommu(Object *obj, Error **errp)
>      }
>  }
>  
> +static int virt_get_num_nested_smmus(VirtMachineState *vms, Error **errp)
> +{
> +    VirtNestedSmmu *nested_smmu;
> +    struct dirent *dent;
> +    DIR *dir = NULL;
> +    int num = 0;
> +
> +    dir = opendir("/sys/class/iommu");
> +    if (!dir) {
> +        error_setg_errno(errp, errno, "couldn't open /sys/class/iommu");
> +        return 0;
> +    }
> +
> +    while ((dent = readdir(dir))) {
> +        if (!strncmp(dent->d_name, "smmu3.0x", 7)) {
> +            nested_smmu = g_new0(VirtNestedSmmu, 1);
> +            nested_smmu->index = num;
> +            nested_smmu->smmu_node = g_strdup(dent->d_name);
> +            QLIST_INSERT_HEAD(&vms->nested_smmu_list, nested_smmu, next);
> +            num++;
> +        }
> +    }
> +
> +    if (num == 0) {
> +        error_setg_errno(errp, errno,
> +                         "couldn't find any SMMUv3 HW to setup nesting");
> +    }
> +
> +    return num;
> +}
> +
>  static void virt_set_iommu(Object *obj, const char *value, Error **errp)
>  {
>      VirtMachineState *vms = VIRT_MACHINE(obj);
> @@ -2676,6 +2707,7 @@ static void virt_set_iommu(Object *obj, const char 
> *value, Error **errp)
>          vms->iommu = VIRT_IOMMU_SMMUV3;
>      } else if (!strcmp(value, "nested-smmuv3")) {
>          vms->iommu = VIRT_IOMMU_NESTED_SMMUV3;
> +        vms->num_nested_smmus = virt_get_num_nested_smmus(vms, errp);
>      } else if (!strcmp(value, "none")) {
>          vms->iommu = VIRT_IOMMU_NONE;
>      } else {
> @@ -3232,6 +3264,9 @@ static void virt_instance_init(Object *obj)
>      /* The default root bus is attached to iommu by default */
>      vms->default_bus_bypass_iommu = false;
>  
> +    /* Default disallows nested SMMU instantiation */
> +    vms->num_nested_smmus = 0;
> +
>      /* Default disallows RAS instantiation */
>      vms->ras = false;
>  
> diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
> index d5cbce1a30..e0c07527c4 100644
> --- a/include/hw/arm/virt.h
> +++ b/include/hw/arm/virt.h
> @@ -135,6 +135,12 @@ struct VirtMachineClass {
>      bool no_ns_el2_virt_timer_irq;
>  };
>  
> +typedef struct VirtNestedSmmu {
> +    int index;
> +    char *smmu_node;
> +    QLIST_ENTRY(VirtNestedSmmu) next;
> +} VirtNestedSmmu;
> +
>  struct VirtMachineState {
>      MachineState parent;
>      Notifier machine_done;
> @@ -153,6 +159,7 @@ struct VirtMachineState {
>      bool ras;
>      bool mte;
>      bool dtb_randomness;
> +    int num_nested_smmus;
>      OnOffAuto acpi;
>      VirtGICType gic_version;
>      IOMMUFDBackend *iommufd;
> @@ -178,6 +185,7 @@ struct VirtMachineState {
>      char *oem_id;
>      char *oem_table_id;
>      bool ns_el2_virt_timer_irq;
> +    QLIST_HEAD(, VirtNestedSmmu) nested_smmu_list;
>  };
>  
>  #define VIRT_ECAM_ID(high) (high ? VIRT_HIGH_PCIE_ECAM : VIRT_PCIE_ECAM)