linux-kernel - Re: [PATCH v1 04/14] iommu/arm-smmu-v3: Add arm_smmu_hw

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Message-ID: <ZBN2tmWoRURvjarc@Asurada-Nvidia>
Date:   Thu, 16 Mar 2023 13:06:14 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
CC:     <jgg@...dia.com>, <will@...nel.org>, <eric.auger@...hat.com>,
        <kevin.tian@...el.com>, <baolu.lu@...ux.intel.com>,
        <joro@...tes.org>, <shameerali.kolothum.thodi@...wei.com>,
        <jean-philippe@...aro.org>, <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 04/14] iommu/arm-smmu-v3: Add arm_smmu_hw_info

On Thu, Mar 16, 2023 at 03:19:27PM +0000, Robin Murphy wrote:

> > > Note that until now it has been extremely fortunate that in pretty much
> > > every case Linux either hasn't supported the affected feature at all, or
> > > has happened to avoid meeting the conditions. Once we do introduce
> > > nesting support that all goes out the window (and I'll have to think
> > > more when reviewing new errata in future...)
> > > 
> > > I've been putting off revisiting all the existing errata to figure out
> > > what we'd need to do until new nesting patches appeared, so I'll try to
> > > get to that soon now. I think in many cases it's likely to be best to
> > > just disallowing nesting entirely on affected implementations.
> > 
> > Do we have already a list of "affected implementations"? Or,
> > we would need to make such a list now? In a latter case, can
> > these affected implementations be detected from their IRD0-5
> > registers, so that we can simply do something in hw_info()?
> 
> Somewhere I have a patch that adds all the IIDR stuff needed for this,
> but I never sent it upstream since the erratum itself was an early
> MMU-600 one which in practice doesn't matter. I'll dig that out and
> update it with what I have in mind.

Nice!

Perhaps we should merge that first, or include in this series
if you don't mind, so that we would be less worried about any
affected platform when releasing the new Linux version having
this nesting feature.

Thanks!
Nic