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

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Message-ID: <aWkU4a1wj5jsWFev@Asurada-Nvidia>
Date: Thu, 15 Jan 2026 08:25:05 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...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 Thu, Jan 15, 2026 at 09:11:51AM -0400, Jason Gunthorpe wrote:
> 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..

The EATS field is completely controlled by the driver. So, we are
safe for now, right?

Should we add this when the driver has the actual support for the
split stage thing?

Thanks
Nicolin