Re: [PATCH v2 5/7] hw/arm/smmuv3-accel: Implement "auto" value for "oas"

[Eric Auger <eric.auger@redhat.com>]

On 4/22/26 10:43 PM, Nathan Chen wrote:
> Allow accelerated SMMUv3 OAS property to be derived from host IOMMU
> capabilities. Derive host values using IOMMU_GET_HW_INFO, retrieving
> OAS from IDR5.
>
> This keeps the OAS value advertised by the virtual SMMU compatible with
> the capabilities of the host SMMUv3, so that the intermediate physical
> addresses (IPA) consumed by host SMMU for stage-2 translation do not
> exceed the host's max supported IPA size.
>
> Signed-off-by: Nathan Chen <nathanc@nvidia.com>
> ---
>  hw/arm/smmuv3-accel.c |  8 +++++++-
>  hw/arm/smmuv3.c       | 15 ++++++++-------
>  2 files changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
> index d13d15a11d..f45e268bde 100644
> --- a/hw/arm/smmuv3-accel.c
> +++ b/hw/arm/smmuv3-accel.c
> @@ -68,6 +68,11 @@ static void smmuv3_accel_auto_finalise(SMMUv3State *s,
>                                 FIELD_EX32(info->idr[1], IDR1, SSIDSIZE));
>      }
>  
> +    if (s->oas == OAS_MODE_AUTO) {
> +        s->idr[5] = FIELD_DP32(s->idr[5], IDR5, OAS,
> +                               FIELD_EX32(info->idr[5], IDR5, OAS));
> +    }
> +
>      accel->auto_finalised = true;
>  }
>  
> @@ -988,7 +993,8 @@ void smmuv3_accel_init(SMMUv3State *s)
>  
>      if (s->ats == ON_OFF_AUTO_AUTO ||
>          s->ril == ON_OFF_AUTO_AUTO ||
> -        s->ssidsize == SSID_SIZE_MODE_AUTO) {
> +        s->ssidsize == SSID_SIZE_MODE_AUTO ||
> +        s->oas == OAS_MODE_AUTO) {
>          s->s_accel->auto_mode = true;
>      }
>  
> diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
> index 07025245e2..39a6f72938 100644
> --- a/hw/arm/smmuv3.c
> +++ b/hw/arm/smmuv3.c
> @@ -1975,9 +1975,11 @@ static bool smmu_validate_property(SMMUv3State *s, Error **errp)
>      }
>  #endif
>  
> -    if (s->oas != OAS_MODE_44 && s->oas != OAS_MODE_48) {
> -        error_setg(errp, "QEMU SMMUv3 model only implements 44 and 48 bit"
> -                   "OAS; other OasMode values are not supported");
> +    if (s->oas != OAS_MODE_44 && s->oas != OAS_MODE_48 &&
> +        s->oas != OAS_MODE_AUTO) {
> +        error_setg(errp, "QEMU SMMUv3 model only implements auto, "
> +                   "44 bit, or 48 bit OAS. Other OasMode values are "
> +                   "not supported.");
>          return false;
>      }
>  
> @@ -1991,7 +1993,7 @@ static bool smmu_validate_property(SMMUv3State *s, Error **errp)
>              return false;
>          }
>          if (s->oas > OAS_MODE_44) {
> -            error_setg(errp, "OAS must be 44 bits when accel=off");
> +            error_setg(errp, "oas must be 44 bits when accel=off");
>              return false;
>          }
>          if (s->ssidsize > SSID_SIZE_MODE_0) {
> @@ -2173,9 +2175,8 @@ static void smmuv3_class_init(ObjectClass *klass, const void *data)
>          "Valid values are on, off, and auto. Defaults to off. "
>          "Please ensure host platform supports ATS before enabling.");
>      object_class_property_set_description(klass, "oas",
> -        "Specify Output Address Size (for accel=on). Supported values "
> -        "are 44 or 48 bits. Defaults to 44 bits. oas=auto is not "
> -        "supported.");
> +        "Set Output Address Size in bits (for accel=on). "
> +        "Valid values are 44, 48, and auto. Defaults to 44 bits.");


same auto mode is not explained. It must be explainer either here of in
qemu-options.hx

when set to 'auto' the oas value is derived from host smmu value.

Besides
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Eric


>      object_class_property_set_description(klass, "ssidsize",
>          "Set number of bits used to represent SubstreamIDs (SSIDs). "
>          "Valid values are 0-20 and auto. Defaults to 0. "