Re: [PATCH v2 4/4] iommu/arm-smmu-v3: Enable HTTU for stage1 with io-pgtable mapping

From: Jason Gunthorpe <jgg@nvidia.com>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>,
	iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	joro@8bytes.org, kevin.tian@intel.com, nicolinc@nvidia.com,
	mshavit@google.com, robin.murphy@arm.com, will@kernel.org,
	joao.m.martins@oracle.com, jiangkunkun@huawei.com,
	zhukeqian1@huawei.com, linuxarm@huawei.com
Subject: Re: [PATCH v2 4/4] iommu/arm-smmu-v3: Enable HTTU for stage1 with io-pgtable mapping
Date: Tue, 23 Apr 2024 14:32:02 -0300	[thread overview]
Message-ID: <20240423173202.GB941030@nvidia.com> (raw)
In-Reply-To: <364b6a6f-048c-426c-a9c4-aabef551e0c0@arm.com>

On Tue, Apr 23, 2024 at 05:45:16PM +0100, Ryan Roberts wrote:
> On 22/02/2024 09:49, Shameer Kolothum wrote:
> > From: Kunkun Jiang <jiangkunkun@huawei.com>
> > 
> > If io-pgtable quirk flag indicates support for hardware update of
> > dirty state, enable HA/HD bits in the SMMU CD and also set the DBM
> > bit in the page descriptor.
> > 
> > And now report the dirty page tracking capability of SMMUv3.
> > 
> > Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
> > Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> > Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
> > Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> > Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> 
> Section 3.13 of the spec states: "Where translation tables are shared between
> CDs that contain the same ASID (within a translation regime), the CD HA and HD
> fields must be identical."
> 
> I don't think the way that smmu domains work, its possible to end up with a
> single pgtable shared between multiple CDs? 

It is possible. iommufd can link a single hwpt -> iommu_domain ->
smmu_domain to many different RIDs and to different PASIDs each with
their own CD.

> So the driver should be able to guarantee this constraint is met?

It is expected to be done by this:

> > @@ -1271,6 +1271,12 @@ void arm_smmu_make_s1_cd(struct arm_smmu_cd *target,
> >  		CTXDESC_CD_0_ASET |
> >  		FIELD_PREP(CTXDESC_CD_0_ASID, smmu_domain->asid)
> >  		);
> > +
> > +	/* To enable dirty flag update, set both Access flag and dirty state update */
> > +	if (pgtbl_cfg->quirks & IO_PGTABLE_QUIRK_ARM_HD)
> > +		target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_HA |
> > +					       CTXDESC_CD_0_TCR_HD);
> > +

This function is the only place that programs the ASID into a CD entry
for the domain, and it always derives the HA/HD bits in the same way
from some immutable value stored in the iommu_domain structure.

Jason

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