Date: Tue, 7 Mar 2023 14:32:09 -0800
From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Baolu Lu <baolu.lu@linux.intel.com>, Jean-Philippe Brucker
 <jean-philippe@linaro.org>, LKML <linux-kernel@vger.kernel.org>,
 iommu@lists.linux.dev, Joerg Roedel <joro@8bytes.org>, Jean-Philippe
 Brucker <jean-philippe@linaro.com>, Dave Hansen <dave.hansen@intel.com>,
 Thomas Gleixner <tglx@linutronix.de>, X86 Kernel <x86@kernel.org>,
 bp@alien8.de, "H. Peter Anvin" <hpa@zytor.com>, Peter Zijlstra
 <peterz@infradead.org>, corbet@lwn.net, vkoul@kernel.org,
 dmaengine@vger.kernel.org, linux-doc@vger.kernel.org, Robin Murphy
 <robin.murphy@arm.com>, Will Deacon <will@kernel.org>, David Woodhouse
 <dwmw2@infradead.org>, Raj Ashok <ashok.raj@intel.com>, "Tian, Kevin"
 <kevin.tian@intel.com>, Yi Liu <yi.l.liu@intel.com>, "Yu, Fenghua"
 <fenghua.yu@intel.com>, Dave Jiang <dave.jiang@intel.com>, Kirill Shutemov
 <kirill.shutemov@linux.intel.com>, jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH v4 3/6] iommu/sva: Stop using ioasid_set for SVA
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Hi Jason,

On Fri, 3 Mar 2023 09:15:45 -0400, Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Fri, Mar 03, 2023 at 05:57:41PM +0800, Baolu Lu wrote:
> > On 2023/3/3 17:32, Jean-Philippe Brucker wrote:  
> > > > I suppose the common thing is reserving some kind of special
> > > > PASIDs.  
> > > Are you planning to use RID_PASID != 0 in VT-d?  Otherwise we could
> > > just communicate min_pasid from the IOMMU driver the same way we do
> > > max_pasid.
> > > 
> > > Otherwise I guess re-introduce a lighter ioasid_alloc() that the IOMMU
> > > driver calls to reserve PASID0/RID_PASID.  
> > 
> > Yes. We probably will use a non-zero RID_PASID in the future. An
> > interface to reserve (or allocate) a PASID from iommu_global_pasid_ida
> > should work then.  
> 
> Just allowing the driver to store XA_ZERO_ENTRY would be fine
> 
It looks like there are incoming users of iommu_sva_find()
https://lore.kernel.org/lkml/20230306163138.587484-1-fenghua.yu@intel.com/T/#m1fc97725a0e56ea269c8bdabacee447070d51846
Should we keep the xa here instead of the global ida?

 
Thanks,

Jacob