linux-kernel - Re: [PATCH v1 1/4] iommu/arm-smmu-v3: Pass in vmid to arm_smmu_make_s2_domain

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Message-ID: <Z_OOukRG0foehmV6@google.com>
Date: Mon, 7 Apr 2025 08:37:14 +0000
From: Pranjal Shrivastava <praan@...gle.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>,
	"will@...nel.org" <will@...nel.org>,
	"robin.murphy@....com" <robin.murphy@....com>,
	"jgg@...dia.com" <jgg@...dia.com>,
	"joro@...tes.org" <joro@...tes.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/4] iommu/arm-smmu-v3: Pass in vmid to
 arm_smmu_make_s2_domain_ste()

On Wed, Mar 05, 2025 at 09:44:30AM -0800, Nicolin Chen wrote:
> On Wed, Mar 05, 2025 at 08:50:17AM +0000, Shameerali Kolothum Thodi wrote:
> > > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > > b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > > index bd9d7c85576a..e08c4ede4b2d 100644
> > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > > @@ -887,7 +887,7 @@ struct arm_smmu_entry_writer_ops {
> > >  void arm_smmu_make_abort_ste(struct arm_smmu_ste *target);
> > >  void arm_smmu_make_s2_domain_ste(struct arm_smmu_ste *target,
> > >  				 struct arm_smmu_master *master,
> > > -				 struct arm_smmu_domain *smmu_domain,
> > > +				 struct arm_smmu_domain *smmu_domain,
> > > u16 vmid,
> > >  				 bool ats_enabled);
> > 
> > Now that vmid is an input, do we need some kind of validation here as
> > at least vmid = 0 is reserved I guess for bypass STEs.
> 
> Perhaps it should do a WARN_ON_ONCE(!vmid), as it doesn't make
> sense for a caller to make an S2-bypass STE with this function.
> 

+1, a warning should suffice as the caller isn't expected to call this
with vmid = 0. For the s2 bypass case, we already set vmid field to 0 in
make_cdtable_ste for clients who *really* want the vmid = 0.

> Thanks
> Nicolin
> 

Thanks
Praan