linux-kernel - Re: [PATCH] iommu: Add Kconfig help text for IOMMU

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Date:   Tue, 9 May 2023 20:06:01 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>, Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>
Subject: Re: [PATCH] iommu: Add Kconfig help text for IOMMU_SVA

On Mon, May 08, 2023 at 10:17:53AM -0700, Linus Torvalds wrote:

> That said, the arm-smmu-v3-sva.c code clearly *also* uses pasid,
> except it seems to really want to call it "ssid".

This code is incorrect.. It is using the mm->pasid to try to deliver
an invalidation, but our new design does not restrict the userspace to
a single PASID, thus it will fail to properly synchronize the ATC in
some degenerate cases. In general the driver needs to be able to go
over a list of PASIDs that the domains are linked to and replicate
invalidations (of any sort) to the whole list. 

It is still a WIP to make this driver implement the driver contract
for PASID logic properly.

> Now, "SSID" is a completely horrible name, as I immediately realized
> when I tried to google for it. So arm64 is just wrong, and we're most
> definitely continuing to call it PASID.

Yes, PASID comes from PCIe so we are using that.

> I'd lean towards just "CONFIG_MM_PASID" or something, but at some
> point this is bikeshedding, and I don't know about any possible
> non-iommu direct uses?

I don't think there is any other use, IOMMU should be the only
consumer of PASID, so it is a fine name as well.

Thanks,
Jason