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Date:   Fri, 20 Apr 2018 16:42:51 -0700
From:   Jacob Pan <jacob.jun.pan@linux.intel.com>
To:     Jean-Philippe Brucker <Jean-Philippe.Brucker@arm.com>
Cc:     Alex Williamson <alex.williamson@redhat.com>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Raj Ashok <ashok.raj@intel.com>,
        Jean Delvare <khali@linux-fr.org>,
        Christoph Hellwig <hch@infradead.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Yi L <yi.l.liu@linux.intel.com>, jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH v4 04/22] iommu/vt-d: add bind_pasid_table function
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On Fri, 20 Apr 2018 19:25:34 +0100
Jean-Philippe Brucker <Jean-Philippe.Brucker@arm.com> wrote:

> On Tue, Apr 17, 2018 at 08:10:47PM +0100, Alex Williamson wrote:
> [...]
> > > +	/* Assign guest PASID table pointer and size order */
> > > +	ctx_lo = (pasidt_binfo->base_ptr & VTD_PAGE_MASK) |
> > > +		(pasidt_binfo->pasid_bits - MIN_NR_PASID_BITS);  
> > 
> > Where does this IOMMU API interface define that base_ptr is 4K
> > aligned or the format of the PASID table?  Are these all
> > standardized or do they vary by host IOMMU?  If they're standards,
> > maybe we could note that and the spec which defines them when we
> > declare base_ptr.  If they're IOMMU specific then I don't
> > understand how we'll match a user provided PASID table to the
> > requirements and format of the host IOMMU. Thanks,  
> 
> On SMMUv3 the minimum alignment for base_ptr is 64 bytes, so a guest
> under a vSMMU might pass a pointer that's not aligned on 4k.
> 
PASID table pointer for VT-d is 4K aligned. 
> Maybe this information could be part of the data passed to userspace
> about IOMMU table formats and features? They're not part of this
> series, but I think we wanted to communicate IOMMU-specific features
> via sysfs.
> 
Agreed, I believe Yi Liu is working on a sysfs interface such that QEMU
can match IOMMU model and features.