linux-kernel - RE: [PATCH v5 0/6] Add Tegra241 (Grace) CMDQV Support (part 1/2)

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Date: Wed, 17 Apr 2024 15:13:52 +0000
From: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Nicolin Chen <nicolinc@...dia.com>, "will@...nel.org" <will@...nel.org>,
	"robin.murphy@....com" <robin.murphy@....com>, "joro@...tes.org"
	<joro@...tes.org>, "thierry.reding@...il.com" <thierry.reding@...il.com>,
	"vdumpa@...dia.com" <vdumpa@...dia.com>, "jonathanh@...dia.com"
	<jonathanh@...dia.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-tegra@...r.kernel.org"
	<linux-tegra@...r.kernel.org>, Jerry Snitselaar <jsnitsel@...hat.com>
Subject: RE: [PATCH v5 0/6] Add Tegra241 (Grace) CMDQV Support (part 1/2)



> -----Original Message-----
> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Wednesday, April 17, 2024 1:25 PM
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
> Cc: Nicolin Chen <nicolinc@...dia.com>; will@...nel.org;
> robin.murphy@....com; joro@...tes.org; thierry.reding@...il.com;
> vdumpa@...dia.com; jonathanh@...dia.com; linux-kernel@...r.kernel.org;
> iommu@...ts.linux.dev; linux-arm-kernel@...ts.infradead.org; linux-
> tegra@...r.kernel.org; Jerry Snitselaar <jsnitsel@...hat.com>
> Subject: Re: [PATCH v5 0/6] Add Tegra241 (Grace) CMDQV Support (part 1/2)
> 
> On Wed, Apr 17, 2024 at 08:01:10AM +0000, Shameerali Kolothum Thodi wrote:
> > We do have plans to revive the SMMUv3 ECMDQ series posted a while back[0]
> > and looking at this series, I am just wondering whether it makes sense to have
> > a similar one with ECMDQ as well?  I see that the NVIDIA VCMDQ has a special
> bit
> > to restrict the commands that can be issued from user space. If we end up
> assigning
> > a ECMDQ to user space, is there any potential risk in doing so?
> 
> I think there is some risk/trouble, ECMDQ needs some enhancement
> before it can be really safe to use from less privileged software, and
> it wasn't designed to have an isolated doorbell page either.
> 
> > Not clear to me what are the major concerns here and maybe we can come up
> with
> > something to address that in kernel.
> 
> I haven't looked deeply but my impression has been the ECMDQ is not
> workable to support virtualization. At a minimum it has no way to
> constrain the command flow to a VMID and to do VSID -> PSID
> translation.

Ok. That makes sense.

> 
> I suggest you talk directly to ARM on this if you are interested in
> this.
> 

Sure. Will check.

Thanks,
Shameer