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

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Date:   Thu, 13 May 2021 12:57:49 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.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>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "wangzhou1@...ilicon.com" <wangzhou1@...ilicon.com>,
        "zhangfei.gao@...aro.org" <zhangfei.gao@...aro.org>,
        "vkoul@...nel.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 Thu, May 13, 2021 at 12:46:21PM -0700, Jacob Pan wrote:
> It seems there are two options:
> 1. Add a new IOMMU API to set up a system PASID with a *separate* IOMMU page
> table/domain, mark the device is PASID only with a flag. Use DMA APIs
> to explicit map/unmap. Based on this PASID-only flag, Vendor IOMMU driver
> will decide whether to use system PASID domain during map/unmap. Not clear
> if we also need to make IOVA==kernel VA.
> 
> 2. Add a new IOMMU API to setup a system PASID which points to init_mm.pgd.
> This API only allows trusted device to bind with the system PASID at its
> own risk. There is no need for DMA API. This is the same as the current
> code except with an explicit API.
> 
> Which option?

Option #1 looks cleaner to me. Option #2 gives access to bits
of memory that the users of system PASID shouldn't ever need
to touch ... just map regions of memory that the kernel has
a "struct page" for.

What does "use DMA APIs to explicitly map/unmap" mean? Is that
for the whole region?

I'm expecting that once this system PASID has been initialized,
then any accelerator device with a kernel use case would use the
same PASID. I.e. DSA for page clearing, IAX for ZSwap compression
& decompression, etc.

-Tony