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: <aXgtmVXUBQuwCR7A@Asurada-Nvidia>
Date: Mon, 26 Jan 2026 19:14:33 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Will Deacon <will@...nel.org>
CC: Jason Gunthorpe <jgg@...dia.com>, <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 v9 6/7] iommu/arm-smmu-v3: Add arm_smmu_invs based
 arm_smmu_domain_inv_range()

On Mon, Jan 26, 2026 at 06:56:34PM +0000, Will Deacon wrote:
> On Mon, Jan 26, 2026 at 12:09:40PM -0400, Jason Gunthorpe wrote:
> > On Mon, Jan 26, 2026 at 04:02:19PM +0000, Will Deacon wrote:
> > > If we do that, can we drop the smp_mb()s from
> > > arm_smmu_install_{old,new}_domain_invs()?
> > 
> > I suppose so, but domain attach isn't a performance path so it depends
> > on your preference for strict pairing of barriers. Currently the two
> > smp_mbs() are paired. Can we reliably pair smp_mb() with dma_wmb()?
> > Are you happy with that clarity?
> 
> Yeah, I think that's ok.
> 
> > My view is attach isn't a performance path, so having extra barriers
> > is fine if it helps understandability.
> 
> I think that the more barriers we have, the harder the code is to
> understand so I would prefer just to have the smp_mb() for the
> write->read case in arm_smmu_domain_inv_range() along with a comment
> explaining why it's needed.
> 
> I think that also means that my concern about the old comments on the
> other patch largely disappears.

I sent v10. Thanks for the insightful reviews!

Nicolin