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

[Nicolin Chen <nicolinc@nvidia.com>]

On Mon, Feb 24, 2025 at 09:53:58PM +0000, Pranjal Shrivastava wrote:
> On Mon, Feb 24, 2025 at 01:31:11PM -0800, Nicolin Chen wrote:
> > On Mon, Feb 24, 2025 at 08:35:56PM +0000, Pranjal Shrivastava wrote:
> > > 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?
> > 
> > No. prepare() and commit() are 1:1. How is it interpreted to have
> > "multiple times"?
> 
> Ohh alright. I was just confused about why do we need to check:
> `if (state->vmaster != master->vmaster)` ?

Hmm, it's probably not necessary, since we always allocate a new
vmaster pointer to the "state" or set a NULL.

I will clean that up a bit.

Thanks
Nicolin