Re: [RFC PATCH v3 12/15] hw/arm/smmuv3-accel: Introduce helpers to batch and issue cache invalidations

[Jonathan Cameron via <qemu-devel@nongnu.org>]

On Mon, 14 Jul 2025 16:59:38 +0100
Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> wrote:

> From: Nicolin Chen <nicolinc@nvidia.com>
> 
> Helpers will batch the commands and issue at once to host SMMUv3.
> 
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> ---
>  hw/arm/smmuv3-accel.c    | 65 ++++++++++++++++++++++++++++++++++++++++
>  hw/arm/smmuv3-accel.h    | 16 ++++++++++
>  hw/arm/smmuv3-internal.h | 12 ++++++++
>  3 files changed, 93 insertions(+)
> 
> diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
> index 04c665ccf5..1298b4f6d0 100644
> --- a/hw/arm/smmuv3-accel.c
> +++ b/hw/arm/smmuv3-accel.c
> @@ -168,6 +168,71 @@ smmuv3_accel_install_nested_ste_range(SMMUState *bs, SMMUSIDRange *range)
>      g_hash_table_foreach(bs->configs, smmuv3_accel_ste_range, range);
>  }
>  
> +/* Update batch->ncmds to the number of execute cmds */

Not obvious what the return value here means. Maybe a comment?

> +bool smmuv3_accel_issue_cmd_batch(SMMUState *bs, SMMUCommandBatch *batch)
> +{
> +    SMMUv3State *s = ARM_SMMUV3(bs);
> +    SMMUv3AccelState *s_accel = s->s_accel;
> +    uint32_t total = batch->ncmds;
> +    IOMMUFDViommu *viommu_core;
> +    int ret;
> +
> +    if (!bs->accel) {
> +        return true;
> +    }
> +
> +    if (!s_accel->viommu) {
> +        return true;
> +    }
> +
> +    viommu_core = &s_accel->viommu->core;
> +    ret = iommufd_backend_invalidate_cache(viommu_core->iommufd,
> +                                           viommu_core->viommu_id,
> +                                           IOMMU_VIOMMU_INVALIDATE_DATA_ARM_SMMUV3,
> +                                           sizeof(Cmd), &batch->ncmds,
> +                                           batch->cmds, NULL);
> +    if (!ret || total != batch->ncmds) {
> +        error_report("%s failed: ret=%d, total=%d, done=%d",
> +                      __func__, ret, total, batch->ncmds);
> +        return ret;

This is reporting an error either way but returning success for the second
condition which looks odd.  Add a comment if intended.

> +    }
> +
> +    batch->ncmds = 0;
> +    return ret;

return true; given I think we know it's true if we get here?

> +}
> +
> +/*
> + * Note: sdev can be NULL for certain invalidation commands
> + * e.g., SMMU_CMD_TLBI_NH_ASID, SMMU_CMD_TLBI_NH_VA etc.
> + */
> +void smmuv3_accel_batch_cmd(SMMUState *bs, SMMUDevice *sdev,
> +                           SMMUCommandBatch *batch, Cmd *cmd,
> +                           uint32_t *cons)
> +{
> +    if (!bs->accel) {
> +        return;
> +    }
> +
> +   /*
> +    * We may end up here for any emulated PCI bridge or root port type
> +    * devices. The batching of commands only matters for vfio-pci endpoint
> +    * devices with Guest S1 translation enabled. Hence check that, if
> +    * sdev is available.
> +    */
> +    if (sdev) {
> +        SMMUv3AccelDevice *accel_dev;
> +        accel_dev = container_of(sdev, SMMUv3AccelDevice, sdev);
> +
> +        if (!accel_dev->s1_hwpt) {
> +            return;
> +        }
> +    }
> +
> +    batch->cmds[batch->ncmds] = *cmd;
> +    batch->cons[batch->ncmds++] = *cons;
> +    return;
Drop this trailing return.

> +}