linux-kernel - Re: [PATCH v6 3/7] iommu/arm-smmu-v3: Introduce a per-domain arm_smmu

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Message-ID: <20251126183610.GL520526@nvidia.com>
Date: Wed, 26 Nov 2025 14:36:10 -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 v6 3/7] iommu/arm-smmu-v3: Introduce a per-domain
 arm_smmu_invs array

On Tue, Nov 25, 2025 at 05:10:08PM -0800, Nicolin Chen wrote:
> From: Jason Gunthorpe <jgg@...dia.com>
> 
> Create a new data structure to hold an array of invalidations that need to
> be performed for the domain based on what masters are attached, to replace
> the single smmu pointer and linked list of masters in the current design.
> 
> Each array entry holds one of the invalidation actions - S1_ASID, S2_VMID,
> ATS or their variant with information to feed invalidation commands to HW.
> It is structured so that multiple SMMUs can participate in the same array,
> removing one key limitation of the current system.
> 
> To maximize performance, a sorted array is used as the data structure. It
> allows grouping SYNCs together to parallelize invalidations. For instance,
> it will group all the ATS entries after the ASID/VMID entry, so they will
> all be pushed to the PCI devices in parallel with one SYNC.
> 
> To minimize the locking cost on the invalidation fast path (reader of the
> invalidation array), the array is managed with RCU.
> 
> Provide a set of APIs to add/delete entries to/from an array, which cover
> cannot-fail attach cases, e.g. attaching to arm_smmu_blocked_domain. Also
> add kunit coverage for those APIs.
> 
> Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Co-developed-by: Nicolin Chen <nicolinc@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h   |  97 +++++++
>  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-test.c  |  92 +++++++
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   | 256 ++++++++++++++++++
>  3 files changed, 445 insertions(+)

New version looks good

Jason