linux-kernel - RE: [PATCH RFC 2/2] iommu/arm-smmu-v3: Bypass SID0 for NXP i.MX95

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Message-ID:
 <PAXPR04MB8459EC5B8A55E7FF10E550AC88462@PAXPR04MB8459.eurprd04.prod.outlook.com>
Date: Wed, 16 Oct 2024 09:02:39 +0000
From: Peng Fan <peng.fan@....com>
To: Pranjal Shrivastava <praan@...gle.com>, Robin Murphy
	<robin.murphy@....com>, Jason Gunthorpe <jgg@...pe.ca>
CC: "Peng Fan (OSS)" <peng.fan@....nxp.com>, Will Deacon <will@...nel.org>,
	Joerg Roedel <joro@...tes.org>, Rob Herring <robh@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Joy Zou
	<joy.zou@....com>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RFC 2/2] iommu/arm-smmu-v3: Bypass SID0 for NXP i.MX95

All,

> Subject: Re: [PATCH RFC 2/2] iommu/arm-smmu-v3: Bypass SID0 for
> NXP i.MX95

Thanks for the discussion on this topic to show much information
that I not foresee.

> 
> On Tue, Oct 15, 2024 at 04:37:25PM +0100, Robin Murphy wrote:
> > On 2024-10-15 4:31 pm, Jason Gunthorpe wrote:
> > > On Tue, Oct 15, 2024 at 04:13:13PM +0100, Robin Murphy wrote:
> > > > On 2024-10-15 1:47 pm, Jason Gunthorpe wrote:
> > > > > On Tue, Oct 15, 2024 at 08:13:28AM +0000, Pranjal Shrivastava
> wrote:
> > > > >
> > > > > > Umm.. this was specific for rmr not a generic thing. I'd
> > > > > > suggest to avoid meddling with the STEs directly for acheiving
> > > > > > bypass. Playing with the iommu domain type could be neater.
> > > > > > Perhaps, modify the
> > > > > > ops->def_domain_type to return an appropriate domain?
> > > > >
> > > > > Yeah, that is the expected way, to force the def_domain_type to
> > > > > IDENTITY and refuse to attach a PAGING/BLOCKED domain.
> > > >
> > > > There is no domain, this is bypassing an arbitrary StreamID not
> > > > associated with any device.
> > >
> > > If the stream ID is going to flow traffic shouldn't it have a DT
> > > node for it? Something must be driving the DMA on this SID, and
> the
> > > kernel does need to know what that is in some way, even for basic
> > > security things like making sure VFIO doesn't get a hold of it :\
> >
> > Exactly, hence this RFC is definitely not the right approach.
> 
> Agreed. I assumed the bypass was needed for a registered SID.

I just reply here, not reply each thread.

The SID is not a registered SID.

Considering the security things, except "iommus = <&smmu 0>"
being added, is there other method for this issue?

Thanks,
Peng.

> 
> >
> > Thanks,
> > Robin.
> 
> Thanks,
> Pranjal