linux-kernel - Re: [PATCH v4 02/11] iommufd: Introduce IOMMUFD_OBJ

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Message-ID: <20241022131554.GF13034@nvidia.com>
Date: Tue, 22 Oct 2024 10:15:54 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, kevin.tian@...el.com,
	will@...nel.org, joro@...tes.org, suravee.suthikulpanit@....com,
	robin.murphy@....com, dwmw2@...radead.org, shuah@...nel.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, eric.auger@...hat.com,
	jean-philippe@...aro.org, mdf@...nel.org, mshavit@...gle.com,
	shameerali.kolothum.thodi@...wei.com, smostafa@...gle.com,
	yi.l.liu@...el.com, aik@....com, zhangfei.gao@...aro.org,
	patches@...ts.linux.dev
Subject: Re: [PATCH v4 02/11] iommufd: Introduce IOMMUFD_OBJ_VIOMMU and its
 related struct

On Tue, Oct 22, 2024 at 04:59:07PM +0800, Baolu Lu wrote:

> Is it feasible to make vIOMMU object more generic, rather than strictly
> tying it to nested translation? For example, a normal paging domain that
> translates gPAs to hPAs could also have a vIOMMU object associated with
> it.
> 
> While we can only support vIOMMU object allocation uAPI for S2 paging
> domains in the context of this series, we could consider leaving the
> option open to associate a vIOMMU object with other normal paging
> domains that are not a nested parent?

Why? The nested parent flavour of the domain is basically free to
create, what reason would be to not do that?

If the HW doesn't support it, then does the HW really need/support a
VIOMMU?

I suppose it could be made up to the driver, but for now I think we
should leave it as is in the core code requiring it until we have a
reason to relax it.

Jason