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From: "Tian, Kevin" <kevin.tian@intel.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>,
	Jean-Philippe Brucker <Jean-Philippe.Brucker@arm.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>,
	"Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
	"Liu, Yi L" <yi.l.liu@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>
Subject: RE: [PATCH v4 04/22] iommu/vt-d: add bind_pasid_table function
Date: Wed, 30 May 2018 03:45:30 +0000	[thread overview]
Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D1911E5F06@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <20180529211746.74f1dd23@w520.home>

> From: Alex Williamson [mailto:alex.williamson@redhat.com]
> Sent: Wednesday, May 30, 2018 11:18 AM
> 
> On Wed, 30 May 2018 01:41:43 +0000
> "Tian, Kevin" <kevin.tian@intel.com> wrote:
> 
> > > From: Alex Williamson [mailto:alex.williamson@redhat.com]
> > > Sent: Wednesday, May 30, 2018 4:09 AM
> > >
> > > On Fri, 20 Apr 2018 16:42:51 -0700
> > > Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:
> > >
> > > > 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.
> > >
> > > Digging this up again since v5 still has this issue.  The IOMMU API is
> > > a kernel internal abstraction of the IOMMU.  sysfs is a userspace
> > > interface.  Are we suggesting that the /only/ way to make use of the
> > > internal IOMMU API here is to have a user provided opaque pasid table
> > > that we can't even do minimal compatibility sanity testing on and we
> > > simply hope that hardware covers all the fault conditions without
> > > taking the host down with it?  I guess we have to assume the latter
> > > since the user has full control of the table, but I have a hard time
> > > getting past lack of internal ability to use the interface and no
> > > ability to provide even the slimmest sanity testing.  Thanks,
> > >
> >
> > checking size, alignment, ... is OK, which I think is already considered
> > by vendor IOMMU driver. However sanity testing table format might
> > be difficult. The initial table provided by guest is likely just all ZEROs.
> > whatever format violation may be caught only when a PASID entry
> > is updated...
> 
> There's sanity testing the actual contents of the table, which I agree
> would be difficult and would likely require some sort of shadowing at
> additional overhead, but what about even basic consistency checking?
> For example, is it possible that due to hardware variations a user
> might generate a table which works on some systems but not others?
> What
> if two table formats are sufficiently similar that the IOMMU driver
> puts an incompatible table in place but it continuously generates
> faults, how do we debug that?  As an intermediary in this whole process
> I'd really rather be able to identify that the user claims to be
> providing a TypeA table but the IOMMU only supports TypeB, so clearly
> this won't work.  I don't see that we have that capability.  Thanks,
> 

I remember we ever discussed to define some vendor/model ID,
which can be retrieved by user space and then passed back when
doing table binding. Then above simple model matching check can
be done accordingly. It is actually a basic requirement when using 
virtio-iommu, same driver expecting to work on all vendor IOMMUs.

However I don't remember whether/where that logic is implemented
in this series (especially when there are two tracks moving in parallel).
I'll leave to Jacob/Jean to further comment.

Thanks
Kevin

  reply	other threads:[~2018-05-30  3:45 UTC|newest]

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-16 21:48 [PATCH v4 00/22] IOMMU and VT-d driver support for Shared Virtual Address (SVA) Jacob Pan
2018-04-16 21:48 ` [PATCH v4 01/22] iommu: introduce bind_pasid_table API function Jacob Pan
2018-04-16 21:48 ` [PATCH v4 02/22] iommu/vt-d: move device_domain_info to header Jacob Pan
2018-04-16 21:48 ` [PATCH v4 03/22] iommu/vt-d: add a flag for pasid table bound status Jacob Pan
2018-04-16 21:48 ` [PATCH v4 04/22] iommu/vt-d: add bind_pasid_table function Jacob Pan
2018-04-17 19:10   ` Alex Williamson
2018-04-20 18:25     ` Jean-Philippe Brucker
2018-04-20 23:42       ` Jacob Pan
2018-05-29 20:09         ` Alex Williamson
2018-05-30  1:41           ` Tian, Kevin
2018-05-30  3:17             ` Alex Williamson
2018-05-30  3:45               ` Tian, Kevin [this message]
2018-05-30 11:53                 ` Jean-Philippe Brucker
2018-05-30 19:52                   ` Jacob Pan
2018-05-31  9:09                     ` Jean-Philippe Brucker
2018-06-05 17:32                       ` Jacob Pan
2018-06-06 11:20                         ` Jean-Philippe Brucker
2018-06-06 21:22                           ` Jacob Pan
2018-06-07 13:21                             ` Jean-Philippe Brucker
2018-04-20 23:22     ` Jacob Pan
2018-04-16 21:48 ` [PATCH v4 05/22] iommu: introduce iommu invalidate API function Jacob Pan
2018-04-20 18:19   ` Jean-Philippe Brucker
2018-04-23 20:43     ` Jacob Pan
2018-04-27 18:07       ` Jean-Philippe Brucker
2018-04-28  2:41         ` Tian, Kevin
2018-05-01 22:58         ` Jacob Pan
2018-05-02  9:31           ` Jean-Philippe Brucker
2018-05-04  4:46             ` Jacob Pan
2018-05-04 18:07               ` Jacob Pan
2018-05-08 10:35                 ` Jean-Philippe Brucker
2018-05-09 12:55                   ` Jacob Pan
2018-05-05 22:19   ` Jerry Snitselaar
2018-05-07 15:41     ` Jacob Pan
2018-04-16 21:48 ` [PATCH v4 06/22] iommu/vt-d: add definitions for PFSID Jacob Pan
2018-04-16 21:48 ` [PATCH v4 07/22] iommu/vt-d: fix dev iotlb pfsid use Jacob Pan
2018-04-16 21:48 ` [PATCH v4 08/22] iommu/vt-d: support flushing more translation cache types Jacob Pan
2018-04-16 21:48 ` [PATCH v4 09/22] iommu/vt-d: add svm/sva invalidate function Jacob Pan
2018-04-17 19:10   ` Alex Williamson
2018-04-20 22:36     ` Jacob Pan
2018-04-16 21:48 ` [PATCH v4 10/22] iommu: introduce device fault data Jacob Pan
2018-04-23 10:11   ` Jean-Philippe Brucker
2018-04-23 11:54     ` Jacob Pan
2018-05-20  8:17   ` Liu, Yi L
2018-05-21 23:16     ` Jacob Pan
2018-04-16 21:49 ` [PATCH v4 11/22] driver core: add per device iommu param Jacob Pan
2018-04-23 10:26   ` Greg Kroah-Hartman
2018-04-16 21:49 ` [PATCH v4 12/22] iommu: introduce device fault report API Jacob Pan
2018-04-23 11:30   ` Jean-Philippe Brucker
2018-04-24 18:29     ` Jacob Pan
2018-04-30 16:53   ` Jean-Philippe Brucker
2018-04-30 18:54     ` Jacob Pan
2018-04-16 21:49 ` [PATCH v4 13/22] iommu: introduce page response function Jacob Pan
2018-04-23 11:47   ` Jean-Philippe Brucker
2018-04-23 12:16     ` Jacob Pan
2018-04-23 15:50       ` Jean-Philippe Brucker
2018-04-16 21:49 ` [PATCH v4 14/22] iommu: handle page response timeout Jacob Pan
2018-04-23 15:36   ` Jean-Philippe Brucker
2018-04-25 15:37     ` Jacob Pan
2018-04-30 10:58       ` Jean-Philippe Brucker
2018-04-30 17:54         ` Jacob Pan
2018-04-16 21:49 ` [PATCH v4 15/22] iommu/config: add build dependency for dmar Jacob Pan
2018-04-16 21:49 ` [PATCH v4 16/22] iommu/vt-d: report non-recoverable faults to device Jacob Pan
2018-04-16 21:49 ` [PATCH v4 17/22] iommu/intel-svm: report device page request Jacob Pan
2018-04-16 21:49 ` [PATCH v4 18/22] iommu/intel-svm: replace dev ops with fault report API Jacob Pan
2018-04-16 21:49 ` [PATCH v4 19/22] iommu/intel-svm: do not flush iotlb for viommu Jacob Pan
2018-04-16 21:49 ` [PATCH v4 20/22] iommu/vt-d: add intel iommu page response function Jacob Pan
2018-04-16 21:49 ` [PATCH v4 21/22] trace/iommu: add sva trace events Jacob Pan
2018-04-16 21:49 ` [PATCH v4 22/22] iommu: use sva invalidate and device fault trace event Jacob Pan
  -- strict thread matches above, loose matches on Subject: below --
2018-03-23  3:11 [PATCH v4 00/22] IOMMU and VT-d driver support for Shared Virtual Address (SVA) Jacob Pan
2018-03-23  3:11 ` [PATCH v4 04/22] iommu/vt-d: add bind_pasid_table function Jacob Pan

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