linux-kernel - Re: [PATCH 3/4] iommu/sva: Support reservation of global PASIDs

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Date:   Fri, 3 Mar 2023 13:47:53 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Jason Gunthorpe <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        "David Woodhouse" <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 3/4] iommu/sva: Support reservation of global PASIDs

Hi Kevin,

On Thu, 2 Mar 2023 09:43:03 +0000, "Tian, Kevin" <kevin.tian@...el.com>
wrote:

> > From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > Sent: Thursday, March 2, 2023 9:00 AM
> > 
> > Global PASID allocation is under IOMMU SVA code since it is the primary
> > use case.  However, some architecture such as VT-d, global PASIDs are
> > necessary for its internal use of DMA API with PASID.  
> 
> No, global PASID is not a VT-d restriction. It's from ENQCMD/S hence a
> device requirement.
I meant VT-d based platforms, it is kind of intertwined in that ENQCMDS
does not restrict RIDPASID!=DMA PASID, vt-d does. Without this
restriction, there wouldn't be a need for this patch. Let me reword.
> > 
> > This patch introduces SVA APIs to reserve and release global PASIDs.
> > 
> > Link: https://lore.kernel.org/all/20230301235646.2692846-4-
> > jacob.jun.pan@...ux.intel.com/
> > Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> > ---
> >  drivers/iommu/iommu-sva.c | 25 +++++++++++++++++++++++++
> >  include/linux/iommu.h     | 14 ++++++++++++++
> >  2 files changed, 39 insertions(+)
> > 
> > diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> > index 8c92a145e15d..cfdeafde88a9 100644
> > --- a/drivers/iommu/iommu-sva.c
> > +++ b/drivers/iommu/iommu-sva.c
> > @@ -149,6 +149,31 @@ u32 iommu_sva_get_pasid(struct iommu_sva
> > *handle)
> >  }
> >  EXPORT_SYMBOL_GPL(iommu_sva_get_pasid);
> > 
> > +ioasid_t iommu_sva_reserve_pasid(ioasid_t min, ioasid_t max)
> > +{
> > +	int ret;
> > +
> > +	if (min == IOMMU_PASID_INVALID || max ==
> > IOMMU_PASID_INVALID ||
> > +	    min == 0 || max < min)
> > +		return IOMMU_PASID_INVALID;
> > +
> > +	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max,
> > GFP_KERNEL);
> > +	if (ret < 0)
> > +		return IOMMU_PASID_INVALID;
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(iommu_sva_reserve_pasid);
> > +  
> 
> I'm not sure it's the right way. It's not related to SVA.
> 
> We should move iommu_global_pasid_ida to iomm.c and then have
> another interface for allocation.
> 
> Above is pretty generic so probably a general one like:
> 
> 	ioasid_t iommu_allocate_global_pasid(struct device *dev)
> 
> internally it can use [1, dev->iommu->max_pasids] as min/max instead
> of passed in from the caller.
sounds good to me, will do.


Thanks,

Jacob