From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Xu Subject: Re: [PATCH v4 1/9] iommu/vt-d: Global PASID name space Date: Wed, 11 Jul 2018 10:48:43 +0800 Message-ID: <20180711024843.GC2359@xz-mi> References: <1531113778-28238-1-git-send-email-baolu.lu@linux.intel.com> <1531113778-28238-2-git-send-email-baolu.lu@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <1531113778-28238-2-git-send-email-baolu.lu@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Lu Baolu Cc: Joerg Roedel , David Woodhouse , ashok.raj@intel.com, sanjay.k.kumar@intel.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, yi.y.sun@intel.com, jacob.jun.pan@intel.com List-Id: iommu@lists.linux-foundation.org On Mon, Jul 09, 2018 at 01:22:50PM +0800, Lu Baolu wrote: [...] > +#ifndef __INTEL_PASID_H > +#define __INTEL_PASID_H > + > +#define PASID_MIN 0x1 > +#define PASID_MAX 0x20000 Could I ask whether there's a reason to explicitly use 0x20000 for the max value? Asked since I saw that the example in the spec gave 20 bits for PASID (please refer to spec ver 3.0 section 3.4.3 figure 3-8). Also I believe that's what I was told by Kevin. I saw that the old per-iommu max value is set to 0x20000, though I'm not sure whether that's still needed since if we're going to have two-level pasid table then AFAIU we don't need physically continuous memory any more (though I saw that we don't yet have two-level pasid table implemented): /* Eventually I'm promised we will get a multi-level PASID table * and it won't have to be physically contiguous. Until then, * limit the size because 8MiB contiguous allocations can be hard * to come by. The limit of 0x20000, which is 1MiB for each of * the PASID and PASID-state tables, is somewhat arbitrary. */ if (iommu->pasid_max > 0x20000) iommu->pasid_max = 0x20000; Thanks, -- Peter Xu