linux-kernel - Re: [PATCH v4 3/6] iommu/sva: Stop using ioasid

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Message-ID: <20230307094203.4dc51ff4@jacob-builder>
Date:   Tue, 7 Mar 2023 09:42:03 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Joerg Roedel <joro@...tes.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        X86 Kernel <x86@...nel.org>, bp@...en8.de,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, corbet@....net,
        vkoul@...nel.org, dmaengine@...r.kernel.org,
        linux-doc@...r.kernel.org, Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.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>,
        Dave Jiang <dave.jiang@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v4 3/6] iommu/sva: Stop using ioasid_set for SVA

Hi Jason,

On Fri, 3 Mar 2023 09:15:45 -0400, Jason Gunthorpe <jgg@...dia.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
> 
So we provide APIs for both?
1. alloc a global PASID, returned by this API
2. try to reserve a global PASID given by the driver, i.e.
	xa_cmpxchg(&iommu_global_pasid_ida.xa, 2, NULL, XA_ZERO_ENTRY,
			 GFP_KERNEL);
seems #1 is sufficient.

Thanks,

Jacob