linux-kernel - Re: [PATCH v6 13/14] iommu/arm-smmu-v3: Report events that belong to devices attached to vIOMMU

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Message-ID: <20250218190846.GA4183890@nvidia.com>
Date: Tue, 18 Feb 2025 15:08:46 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, corbet@....net, will@...nel.org, joro@...tes.org,
	suravee.suthikulpanit@....com, robin.murphy@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com, shuah@...nel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org,
	eric.auger@...hat.com, jean-philippe@...aro.org, mdf@...nel.org,
	mshavit@...gle.com, shameerali.kolothum.thodi@...wei.com,
	smostafa@...gle.com, ddutile@...hat.com, yi.l.liu@...el.com,
	patches@...ts.linux.dev
Subject: Re: [PATCH v6 13/14] iommu/arm-smmu-v3: Report events that belong to
 devices attached to vIOMMU

On Tue, Feb 18, 2025 at 11:02:23AM -0800, Nicolin Chen wrote:
> > > > This already holds the streams_mutex across all of this, do you think
> > > > we should get rid of the vmaster_rwsem and hold the streams_mutex on
> > > > write instead?
> > > 
> > > They are per master v.s. per smmu. The latter one would make master
> > > commits/attaches exclusive, which feels unnecessary to me, although
> > > it would make the code here slightly cleaner..
> > 
> > I'd pay the cost on the attach side to have a single lock on the fault
> > side..
> 
> OK. Maybe a small patch to turn the streams_mutex to streams_rwsem?

I don't think the interrupt path is multithreaded, is it? So only 1
reader anyhow?

Jason