linux-kernel - Re: [PATCH rc v5 1/4] iommu/arm-smmu-v3: Add update

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Message-ID: <20260115131151.GA1081267@nvidia.com>
Date: Thu, 15 Jan 2026 09:11:51 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Will Deacon <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, xueshuai@...ux.alibaba.com, smostafa@...gle.com
Subject: Re: [PATCH rc v5 1/4] iommu/arm-smmu-v3: Add update_safe bits to fix
 STE update sequence

On Tue, Jan 13, 2026 at 04:51:12PM -0400, Jason Gunthorpe wrote:
> > -       safe_bits[1] |= cpu_to_le64(STRTAB_STE_1_EATS);
> > +       if (!((cur[2] | target[2]) & cpu_to_le64(STRTAB_STE_2_S2S)))
> > +               safe_bits[1] |= cpu_to_le64(
> > +                       FIELD_PREP(STRTAB_STE_1_EATS, STRTAB_STE_1_EATS_TRANS));
> > --------------------------------------------------------------------------
> > 
> > @will, does this look good to you? I can send a v7 with this.
> 
> That is an easy way to address Will's observation, makes sense to me.

Ah, but it looks like it can generate an errant view of a EATS that is
neither old or new. Ie value 3, reserved.

I think you should just check if old or new has EATS bit 1 set:

if (!((cur[2] | target[2]) & cpu_to_le64(STRTAB_STE_2_S2S)) &&
    !((cur[1] | target[1]) & cpu_to_le64(FIELD_PREP(STRTAB_STE_1_EATS, 2))))

Which the current driver never does..

Jason