linux-kernel - Re: [PATCH 2/2] iommu/ioasid: Remove custom IOASID allocator

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Date:   Mon, 13 Feb 2023 10:34:55 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     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>,
        David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 2/2] iommu/ioasid: Remove custom IOASID allocator

Hi Jean-Philippe,

On Mon, 13 Feb 2023 16:20:29 +0000, Jean-Philippe Brucker
<jean-philippe@...aro.org> wrote:

> On Fri, Feb 10, 2023 at 03:02:06PM -0800, Jacob Pan wrote:
> > Custom allocator feature was introduced to support VT-d's virtual
> > command, an enlightened interface designed for VMs to allocate PASIDs
> > from the host.
> > 
> > As we remove/withdraw the VT-d virtual command feature, the sole user
> > of custom allocator, we can safely remove the custom allocator as well.
> > Effectively, this will return IOASID core to the original simple global
> > namespace allocator.
> > 
> > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>  
> 
> You can also drop the spinlock.h include. With that:
> 
good catch, thanks
> Reviewed-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
> 
> On a related note, it looks like 100b8a14a370 ("iommu/vt-d: Add pasid
> private data helpers") removed the last user of ioasid_set_data(). I guess
> that could be dropped too, unless you plan to still use it?
> 
You are right, will remove.
I was planning on the other way around which will convert VT-d's private
pasid data helpers to common ioasid code, but when I look closer the
private pasid xa is just holding a list of pasid/mm which could be per iommu
not global. Another cleanup I suppose.

> We could also merge ioasid.c into iommu-sva.c at this point, since I
> haven't seen any interest for having multiple IOASID sets on Arm, but I'm
> not sure what the current plan is for vSVA on x86.
VT-d do plan to use global PASIDs for DMA API with PASIDs since the
work submited via ENQCMDS must use a PASID must != RIDPASID.
https://lore.kernel.org/lkml/20220518182120.1136715-1-jacob.jun.pan@linux.intel.com/T/

So I was thinking a separate ioasid_set for devices that allocates global
PASIDs for DMA API usage. ioasid_set will be useful here for limiting
lookup and resource management. e.g. PASIDs used under in-kernel DMA API
are not subject to cgroups.


> Thanks,
> Jean
> 
> 


Thanks,

Jacob