linux-kernel - Re: [PATCH rc v1 3/4] iommu/arm-smmu-v3: Ignore STE EATS when computing the update sequence

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Message-ID: <20251206194637.GH1219718@nvidia.com>
Date: Sat, 6 Dec 2025 15:46:37 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: will@...nel.org, robin.murphy@....com, joro@...tes.org,
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, skolothumtho@...dia.com,
	praan@...gle.com
Subject: Re: [PATCH rc v1 3/4] iommu/arm-smmu-v3: Ignore STE EATS when
 computing the update sequence

On Fri, Dec 05, 2025 at 04:52:02PM -0800, Nicolin Chen wrote:
> From: Jason Gunthorpe <jgg@...dia.com>
> 
> If a VM want to toggle EATS off the hypervisor will see EATS change to 0
> and insert a V=0 breaking update into the STE even though the VM did not
> ask for that.

"EATS off at the same time as changing CFG"

In bare metal EATS is ignored by CFG=ABORT/BYPASS which is why this
doesn't cause a problem until we have nested where CFG is always a
variation of S2 trans that does use EATS.

Jason