Date:   Tue, 7 Mar 2023 09:42:03 -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
Message-ID: <20230307094203.4dc51ff4@jacob-builder>
In-Reply-To: <ZAHzAa0mnilf0N9K@nvidia.com>
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        <3b2c6fe9-821f-9b84-acb6-777e8517a0fc@linux.intel.com>
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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
> 
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