Re: [PATCH v7 12/14] iommu/arm-smmu-v3: Introduce struct arm_smmu_vmaster

Pranjal Shrivastava
2025-02-24T20:36:08Z

oN sAt, Feb 22, 2025 at 07:54:09AM -0800, Nicolin Chen wrote:
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> index 5aa2e7af58b4..364d8469a480 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> @@ -85,6 +85,59 @@ static void arm_smmu_make_nested_domain_ste(
> }
> }
>
> +int arm_smmu_attach_prepare_vmaster(struct arm_smmu_attach_state *state,
> + struct iommu_domain *domain)
> +{
> + struct arm_smmu_nested_domain *nested_domain;
> + struct arm_smmu_vmaster *vmaster;
> + unsigned long vsid;
> + int ret;
> +
> + iommu_group_mutex_assert(state->master->dev);
> +
> + if (domain->type != IOMMU_DOMAIN_NESTED)
> + return 0;
> + nested_domain = to_smmu_nested_domain(domain);
> +
> + /* Skip invalid vSTE */
> + if (!(nested_domain->ste[0] & cpu_to_le64(STRTAB_STE_0_V)))
> + return 0;
> +
> + ret = iommufd_viommu_get_vdev_id(&nested_domain->vsmmu->core,
> + state->master->dev, &vsid);
> + if (ret)
> + return ret;
> +
> + vmaster = kzalloc(sizeof(*vmaster), GFP_KERNEL);
> + if (!vmaster)
> + return -ENOMEM;
> + vmaster->vsmmu = nested_domain->vsmmu;
> + vmaster->vsid = vsid;
> + state->vmaster = vmaster;
> +
> + return 0;
> +}
> +
> +void arm_smmu_attach_commit_vmaster(struct arm_smmu_attach_state *state)
> +{
> + struct arm_smmu_master *master = state->master;
> +
> + mutex_lock(&master->smmu->streams_mutex);
> + if (state->vmaster != master->vmaster) {
> + kfree(master->vmaster);
> + master->vmaster = state->vmaster;
> + }

Does this condition suggest that we might end up calling
`arm_smmu_attach_prepare_vmaster()` multiple times before __actually__
commiting to a vmaster?

> + mutex_unlock(&master->smmu->streams_mutex);
> +}
> +
> +void arm_smmu_master_clear_vmaster(struct arm_smmu_master *master)
> +{
> + mutex_lock(&master->smmu->streams_mutex);
> + kfree(master->vmaster);
> + master->vmaster = NULL;
> + mutex_unlock(&master->smmu->streams_mutex);
> +}
> +
> static int arm_smmu_attach_dev_nested(struct iommu_domain *domain,
> struct device *dev)
> {
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 358072b4e293..9e50bcee69d1 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2803,6 +2803,7 @@ int arm_smmu_attach_prepare(struct arm_smmu_attach_state *state,
> struct arm_smmu_domain *smmu_domain =
> to_smmu_domain_devices(new_domain);
> unsigned long flags;
> + int ret;
>
> /*
> * arm_smmu_share_asid() must not see two domains pointing to the same
> @@ -2832,9 +2833,15 @@ int arm_smmu_attach_prepare(struct arm_smmu_attach_state *state,
> }
>
> if (smmu_domain) {
> + ret = arm_smmu_attach_prepare_vmaster(state, new_domain);

IMO, this adds a little confusion for folks not using iommufd.

I guess it'd be cleaner if we invoke this below within the:
`if (new_domain->type == IOMMU_DOMAIN_NESTED)` condition instead of
simply returning from the function if the new_domain->type isn't NESTED.

> + if (ret)
> + return ret;
> +
> master_domain = kzalloc(sizeof(*master_domain), GFP_KERNEL);
> - if (!master_domain)
> + if (!master_domain) {
> + kfree(state->vmaster);
> return -ENOMEM;
> + }
> master_domain->master = master;
> master_domain->ssid = state->ssid;
> if (new_domain->type == IOMMU_DOMAIN_NESTED)
> @@ -2861,6 +2868,7 @@ int arm_smmu_attach_prepare(struct arm_smmu_attach_state *state,
> spin_unlock_irqrestore(&smmu_domain->devices_lock,
> flags);
> kfree(master_domain);
> + kfree(state->vmaster);
> return -EINVAL;
> }
>
> @@ -2893,6 +2901,8 @@ void arm_smmu_attach_commit(struct arm_smmu_attach_state *state)
>
> lockdep_assert_held(&arm_smmu_asid_lock);
>
> + arm_smmu_attach_commit_vmaster(state);
> +
> if (state->ats_enabled && !master->ats_enabled) {
> arm_smmu_enable_ats(master);
> } else if (state->ats_enabled && master->ats_enabled) {
> @@ -3162,6 +3172,7 @@ static int arm_smmu_attach_dev_identity(struct iommu_domain *domain,
> struct arm_smmu_ste ste;
> struct arm_smmu_master *master = dev_iommu_priv_get(dev);
>
> + arm_smmu_master_clear_vmaster(master);
> arm_smmu_make_bypass_ste(master->smmu, &ste);
> arm_smmu_attach_dev_ste(domain, dev, &ste, STRTAB_STE_1_S1DSS_BYPASS);
> return 0;
> @@ -3180,7 +3191,9 @@ static int arm_smmu_attach_dev_blocked(struct iommu_domain *domain,
> struct device *dev)
> {
> struct arm_smmu_ste ste;
> + struct arm_smmu_master *master = dev_iommu_priv_get(dev);
>
> + arm_smmu_master_clear_vmaster(master);
> arm_smmu_make_abort_ste(&ste);
> arm_smmu_attach_dev_ste(domain, dev, &ste,
> STRTAB_STE_1_S1DSS_TERMINATE);
>

Thanks,
Praan