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

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Wednesday, April 17, 2024 1:25 PM
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>
> Cc: Nicolin Chen <nicolinc@xxxxxxxxxx>; will@xxxxxxxxxx;
> robin.murphy@xxxxxxx; joro@xxxxxxxxxx; thierry.reding@xxxxxxxxx;
> vdumpa@xxxxxxxxxx; jonathanh@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> iommu@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> tegra@xxxxxxxxxxxxxxx; Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
> 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