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

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Message-ID: <Z735AMlhP29YEndU@google.com>
Date: Tue, 25 Feb 2025 17:08:16 +0000
From: Pranjal Shrivastava <praan@...gle.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Jason Gunthorpe <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 Tue, Feb 25, 2025 at 08:41:27AM -0800, Nicolin Chen wrote:
> On Tue, Feb 25, 2025 at 12:02:25PM -0400, Jason Gunthorpe wrote:
> > On Mon, Feb 24, 2025 at 03:45:33PM -0800, Nicolin Chen wrote:
> > 
> > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
> > > @@ -95,8 +95,6 @@ int arm_smmu_attach_prepare_vmaster(struct arm_smmu_attach_state *state,
> > >  
> > >  	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 */
> > > @@ -122,19 +120,9 @@ 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;
> > > -	}
> > > -	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;
> > > +	master->vmaster = state->vmaster;
> > >  	mutex_unlock(&master->smmu->streams_mutex);
> > >  }
> > 
> > I'd leave the clear_vmaster just for clarity. Commit should not be
> > unpaired with prepare in the other functions.
> > 
> > It looks fine with this on top too
> > 
> > Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> 
> Ack. I added it back and a #ifdef to the vmaster: 
> 
> +void arm_smmu_master_clear_vmaster(struct arm_smmu_master *master)
> +{
> +       struct arm_smmu_attach_state state = { .master = master };
> +
> +       arm_smmu_attach_commit_vmaster(&state);
> +}
> [...]
> @@ -824,6 +829,9 @@ struct arm_smmu_master {
>         struct arm_smmu_device          *smmu;
>         struct device                   *dev;
>         struct arm_smmu_stream          *streams;
> +#ifdef CONFIG_ARM_SMMU_V3_IOMMUFD
> +       struct arm_smmu_vmaster         *vmaster; /* use smmu->streams_mutex */
> +#endif
>         /* Locked by the iommu core using the group mutex */
>         struct arm_smmu_ctx_desc_cfg    cd_table;
>         unsigned int                    num_streams;
> @@ -972,6 +980,9 @@ struct arm_smmu_attach_state {
>         bool disable_ats;
>         ioasid_t ssid;
>         /* Resulting state */
> +#ifdef CONFIG_ARM_SMMU_V3_IOMMUFD
> +       struct arm_smmu_vmaster *vmaster;
> +#endif
>         bool ats_enabled;
>  };
> 

Umm.. I'm not too sure how I feel about these #ifdefs _between_ a struct
definition. Given that currently, the arm_smmu_v3.h file doesn't have
such `#ifdef CONFIG`s between structs. I'd say, in case
CONFIG_ARM_SMMU_V3_IOMMUFD is turned off, we can simply leave the
vmaster ptr NULL?


-Praan