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: <Z7TfC4fmvm4e6fEb@nvidia.com>
Date: Tue, 18 Feb 2025 11:27:07 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...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 03:08:46PM -0400, Jason Gunthorpe wrote:
> 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?

Right, it's IRQF_ONESHOT. I will keep that unchanged.

Thanks
Nicolin