Date:   Fri, 3 Mar 2023 09:32:35 +0000
From:   Jean-Philippe Brucker <jean-philippe@linaro.org>
To:     Baolu Lu <baolu.lu@linux.intel.com>
Cc:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>, iommu@lists.linux.dev,
        Jason Gunthorpe <jgg@nvidia.com>,
        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>
Subject: Re: [PATCH v4 3/6] iommu/sva: Stop using ioasid_set for SVA
Message-ID: <20230303093235.GB361458@myrica>
References: <20230301235646.2692846-1-jacob.jun.pan@linux.intel.com>
 <20230301235646.2692846-4-jacob.jun.pan@linux.intel.com>
 <3b7fb4d3-1fe9-a3be-46ad-c271be9f96c7@linux.intel.com>
 <20230302091707.58d59964@jacob-builder>
 <794c7dad-2e62-3afa-ea10-92179b0d1659@linux.intel.com>
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On Fri, Mar 03, 2023 at 10:24:42AM +0800, Baolu Lu wrote:
> > > > -int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t
> > > > max) +static int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t
> > > > min, ioasid_t max) {
> > > > -	int ret = 0;
> > > > -	ioasid_t pasid;
> > > > +	int ret;
> > > > -	if (min == INVALID_IOASID || max == INVALID_IOASID ||
> > > > +	if (min == IOMMU_PASID_INVALID || max == IOMMU_PASID_INVALID ||
> > > >    	    min == 0 || max < min)
> > > 
> > > It's irrelevant to this patch. Just out of curiosity, why do we need to
> > > exclude PASID 0 here? I just had a quick look at PCI spec section 6.20.
> > > The spec does not state that PASID 0 is invalid.
> > > 
> > my understanding is that ARM reserves PASID0, unlike VT-d where RID_PASID
> > is programmable.

It does, but that's specific to the IOMMU driver so we shouldn't check it
here.

> 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.

Thanks,
Jean