linux-kernel - Re: [PATCH v6 4/7] iommu/arm-smmu-v3: Pre-allocate a per-master invalidation array

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Message-ID: <20251126183649.GM520526@nvidia.com>
Date: Wed, 26 Nov 2025 14:36:49 -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 4/7] iommu/arm-smmu-v3: Pre-allocate a per-master
 invalidation array

On Tue, Nov 25, 2025 at 05:10:09PM -0800, Nicolin Chen wrote:
> When a master is attached from an old domain to a new domain, it needs to
> build an invalidation array to delete and add the array entries from/onto
> the invalidation arrays of those two domains, passed via the to_merge and
> to_unref arguments into arm_smmu_invs_merge/unref() respectively.
> 
> Since the master->num_streams might differ across masters, a memory would
> have to be allocated when building an to_merge/to_unref array which might
> fail with -ENOMEM.
> 
> On the other hand, an attachment to arm_smmu_blocked_domain must not fail
> so it's the best to avoid any memory allocation in that path.
> 
> Pre-allocate a fixed size invalidation array for every master. This array
> will be used as a scratch to fill dynamically when building a to_merge or
> to_unref invs array. Sort fwspec->ids in an ascending order to fit to the
> arm_smmu_invs_merge() function.
> 
> Co-developed-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  8 ++++
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 41 +++++++++++++++++++--
>  2 files changed, 45 insertions(+), 4 deletions(-)

Looks good and addresses Will's remark

Jason