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

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Message-ID: <Z7zqdrQn7Q8yXfcn@google.com>
Date: Mon, 24 Feb 2025 21:53:58 +0000
From: Pranjal Shrivastava <praan@...gle.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, corbet@....net, will@...nel.org,
	joro@...tes.org, suravee.suthikulpanit@....com,
	robin.murphy@....com, dwmw2@...radead.org, baolu.lu@...ux.intel.com,
	shuah@...nel.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
	eric.auger@...hat.com, jean-philippe@...aro.org, mdf@...nel.org,
	mshavit@...gle.com, shameerali.kolothum.thodi@...wei.com,
	smostafa@...gle.com, ddutile@...hat.com, yi.l.liu@...el.com,
	patches@...ts.linux.dev
Subject: Re: [PATCH v7 12/14] iommu/arm-smmu-v3: Introduce struct
 arm_smmu_vmaster

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)` ?

> 
> > > +	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.
> 
> But the arm_smmu_attach_commit_vmaster() still has to be
> unconditional as !NESTED domain should clean the vamster away..
> 

Ack. Right.

Thanks,
Praan