linux-kernel - Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit flags

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Message-ID: <20210511163521.GN1002214@nvidia.com>
Date:   Tue, 11 May 2021 13:35:21 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Christoph Hellwig <hch@...radead.org>,
        Yi Liu <yi.l.liu@...el.com>, Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Dave Jiang <dave.jiang@...el.com>, wangzhou1@...ilicon.com,
        zhangfei.gao@...aro.org, vkoul@...nel.org,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit
 flags

On Tue, May 11, 2021 at 09:14:52AM -0700, Jacob Pan wrote:

> > Honestly, I'm not convinced we should have "kernel SVA" at all.. Why
> > does IDXD use normal DMA on the RID for kernel controlled accesses?
> 
> Using SVA simplifies the work submission, there is no need to do map/unmap.
> Just bind PASID with init_mm, then submit work directly either with ENQCMDS
> (supervisor version of ENQCMD) to a shared workqueue or put the supervisor
> PASID in the descriptor for dedicated workqueue.

That is not OK, protable drivers in Linux have to sue dma map/unmap
calls to manage cache coherence. PASID does not opt out of any of
that.

I dislike this whole idea a lot. A single driver should not opt itself
out of IOMMU based security "just because"

Jason