linux-kernel - Re: [PATCH v4 5/7] iommu/arm-smmu-v3: Populate smmu

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Message-ID: <20251107194932.GC1932966@nvidia.com>
Date: Fri, 7 Nov 2025 15:49:32 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: will@...nel.org, jean-philippe@...aro.org, robin.murphy@....com,
	joro@...tes.org, balbirs@...dia.com, miko.lenczewski@....com,
	peterz@...radead.org, kevin.tian@...el.com, praan@...gle.com,
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/7] iommu/arm-smmu-v3: Populate smmu_domain->invs
 when attaching masters

On Mon, Oct 27, 2025 at 11:54:19AM -0700, Nicolin Chen wrote:
> Update the invs array with the invalidations required by each domain type
> during attachment operations.
> 
> Only an SVA domain or a paging domain will have an invs array:
>  a. SVA domain will add an INV_TYPE_S1_ASID per SMMU and an INV_TYPE_ATS
>     per SID
> 
>  b. Non-nesting-parent paging domain with no ATS-enabled master will add
>     a single INV_TYPE_S1_ASID or INV_TYPE_S2_VMID per SMMU
> 
>  c. Non-nesting-parent paging domain with ATS-enabled master(s) will do
>     (b) and add an INV_TYPE_ATS per SID
> 
>  d. Nesting-parent paging domain will add an INV_TYPE_S2_VMID followed by
>     an INV_TYPE_S2_VMID_S1_CLEAR per vSMMU. For an ATS-enabled master, it
>     will add an INV_TYPE_ATS_FULL per SID
> 
>  Note that case #d prepares for a future implementation of VMID allocation
>  which requires a followup series for S2 domain sharing. So when a nesting
>  parent domain is attached through a vSMMU instance using a nested domain.
>  VMID will be allocated per vSMMU instance v.s. currectly per S2 domain.
> 
> The per-domain invalidation is not needed until the domain is attached to
> a master (when it starts to possibly use TLB). This will make it possible
> to attach the domain to multiple SMMUs and avoid unnecessary invalidation
> overhead during teardown if no STEs/CDs refer to the domain. It also means
> that when the last device is detached, the old domain must flush its ASID
> or VMID, since any new iommu_unmap() call would not trigger invalidations
> given an empty domain->invs array.
> 
> Introduce some arm_smmu_invs helper functions for building scratch arrays,
> preparing and installing old/new domain's invalidation arrays.
> 
> Co-developed-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  17 ++
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 242 +++++++++++++++++++-
>  2 files changed, 258 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason