linux-kernel - Re: [PATCH v9 6/7] iommu/arm-smmu-v3: Add arm_smmu_invs based arm_smmu_domain_inv

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Message-ID: <aXjqBy2sWAUMm/aY@Asurada-Nvidia>
Date: Tue, 27 Jan 2026 08:38:31 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: <jgg@...dia.com>, Pranjal Shrivastava <praan@...gle.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>,
	<linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 6/7] iommu/arm-smmu-v3: Add arm_smmu_invs based
 arm_smmu_domain_inv_range()

Hi Pranjal,

Sorry, I missed this!

On Fri, Jan 23, 2026 at 09:48:37AM +0000, Pranjal Shrivastava wrote:
> On Fri, Dec 19, 2025 at 12:11:28PM -0800, Nicolin Chen wrote:
> > +	/*
> > +	 * Avoid locking unless ATS is being used. No ATC invalidation can be
> > +	 * going on after a domain is detached.
> > +	 */
> > +	if (invs->has_ats) {
> > +		read_lock(&invs->rwlock);
> 
> Shouldn't these be read_lock_irqsave for all rwlock variants here? 
> Invalidations might happen in IRQ context as well..
> 
> > +		__arm_smmu_domain_inv_range(invs, iova, size, granule, leaf);
> > +		read_unlock(&invs->rwlock);

It was kept from the older versions where we had a trylock. Jason
had an insight about this, mainly for less latency on invalidation
threads.

Yet, now we have a plain locking. TBH, I can't find a good reason
justifying this. And it does look a bit unsafe to me. So, I think
I will just change to the _irqsave version. (Jason?)

Thanks
Nicolin