linux-kernel - Re: [PATCH rfcv1 5/8] iommu/arm-smmu-v3: Pre-allocate a per-master invalidation array

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Message-ID: <20250908153604.GB789684@nvidia.com>
Date: Mon, 8 Sep 2025 12:36:04 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: will@...nel.org, robin.murphy@....com, joro@...tes.org,
	jean-philippe@...aro.org, miko.lenczewski@....com,
	balbirs@...dia.com, peterz@...radead.org, smostafa@...gle.com,
	kevin.tian@...el.com, praan@...gle.com, zhangzekun11@...wei.com,
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH rfcv1 5/8] iommu/arm-smmu-v3: Pre-allocate a per-master
 invalidation array

On Sat, Sep 06, 2025 at 12:45:58AM -0700, Nicolin Chen wrote:
 
> One thing that I noticed is that group mutex alone isn't enough,
> because there can be two arm_smmu_build_invs() calls during the
> same attach_dev callback. And the second one would overwrite.

Well the group mutex is what makes it non-concurrent. Two things using
it sequentially within the same thread are a different issue

Jason