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From: "Tian, Kevin" <kevin.tian@intel.com>
To: "Liu, Yi L" <yi.l.liu@intel.com>, Stefan Hajnoczi <stefanha@gmail.com>
Cc: "jean-philippe@linaro.org" <jean-philippe@linaro.org>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"Sun, Yi Y" <yi.y.sun@intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>, "Wu, Hao" <hao.wu@intel.com>,
	"Tian, Jun J" <jun.j.tian@intel.com>
Subject: RE: [PATCH v3 02/14] iommu: Report domain nesting info
Date: Tue, 30 Jun 2020 02:00:49 +0000	[thread overview]
Message-ID: <MWHPR11MB1645B09EBDC76514ADC897A68C6F0@MWHPR11MB1645.namprd11.prod.outlook.com> (raw)
In-Reply-To: <DM5PR11MB1435FC14F2E8AC075DE41205C36E0@DM5PR11MB1435.namprd11.prod.outlook.com>

> From: Liu, Yi L <yi.l.liu@intel.com>
> Sent: Monday, June 29, 2020 8:23 PM
> 
> Hi Stefan,
> 
> > From: Stefan Hajnoczi <stefanha@gmail.com>
> > Sent: Monday, June 29, 2020 5:25 PM
> >
> > On Wed, Jun 24, 2020 at 01:55:15AM -0700, Liu Yi L wrote:
> > > +/*
> > > + * struct iommu_nesting_info - Information for nesting-capable IOMMU.
> > > + *				user space should check it before using
> > > + *				nesting capability.
> > > + *
> > > + * @size:	size of the whole structure
> > > + * @format:	PASID table entry format, the same definition with
> > > + *		@format of struct iommu_gpasid_bind_data.
> > > + * @features:	supported nesting features.
> > > + * @flags:	currently reserved for future extension.
> > > + * @data:	vendor specific cap info.
> > > + *
> > > + * +---------------+----------------------------------------------------+
> > > + * | feature       |  Notes                                             |
> > > + *
> >
> +===============+===============================================
> ====
> > =+
> > > + * | SYSWIDE_PASID |  Kernel manages PASID in system wide, PASIDs
> used  |
> > > + * |               |  in the system should be allocated by host kernel  |
> > > + * +---------------+----------------------------------------------------+
> > > + * | BIND_PGTBL    |  bind page tables to host PASID, the PASID could   |
> > > + * |               |  either be a host PASID passed in bind request or  |
> > > + * |               |  default PASIDs (e.g. default PASID of aux-domain) |
> > > + * +---------------+----------------------------------------------------+
> > > + * | CACHE_INVLD   |  mandatory feature for nesting capable IOMMU
> |
> > > + * +---------------+----------------------------------------------------+
> >
> > This feature description is vague about what CACHE_INVLD does and how
> to
> > use it. If I understand correctly, the presence of this feature means
> > that VFIO_IOMMU_NESTING_OP_CACHE_INVLD must be used?
> >
> > The same kind of clarification could be done for SYSWIDE_PASID and
> > BIND_PGTBL too.
> 
> For SYSWIDE_PASID and BIND_PGTBL, yes, presence of the feature bit
> means must use. So the two are requirements to user space if it wants
> to setup nesting. While for CACHE_INVLD, it's kind of availability
> here. How about removing CACHE_INVLD as presence of BIND_PGTBL should
> indicates support of CACHE_INVLD?
> 

So far this assumption is correct but it may not be true when thinking forward.
For example, a vendor might find a way to allow the owner of 1st-level page
table to directly invalidate cache w/o going through host IOMMU driver. From
this angle I feel explicitly reporting this capability is more robust.

Regarding to the description, what about below?

--
SYSWIDE_PASID: PASIDs are managed in system-wide, instead of per device.
When a device is assigned to userspace or VM, proper uAPI (provided by 
userspace driver framework, e.g. VFIO) must be used to allocate/free PASIDs
for the assigned device.

BIND_PGTBL: The owner of the first-level/stage-1 page table must explicitly 
bind the page table to associated PASID (either the one specified in bind 
request or the default PASID of the iommu domain), through VFIO_IOMMU
_NESTING_OP

CACHE_INVLD: The owner of the first-level/stage-1 page table must
explicitly invalidate the IOMMU cache through VFIO_IOMMU_NESTING_OP,
according to vendor-specific requirement when changing the page table.
--

Thanks
Kevin



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  reply	other threads:[~2020-06-30  2:00 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-24  8:55 [PATCH v3 00/14] vfio: expose virtual Shared Virtual Addressing to VMs Liu Yi L
2020-06-24  8:55 ` [PATCH v3 01/14] vfio/type1: Refactor vfio_iommu_type1_ioctl() Liu Yi L
2020-07-02 21:21   ` Alex Williamson
2020-07-03  3:46     ` Liu, Yi L
2020-06-24  8:55 ` [PATCH v3 02/14] iommu: Report domain nesting info Liu Yi L
2020-06-26  7:47   ` Jean-Philippe Brucker
2020-06-26 16:04     ` Robin Murphy
2020-06-27  6:53       ` Liu, Yi L
2020-06-30  1:20         ` Tian, Kevin
2020-06-27  6:14     ` Liu, Yi L
2020-06-29  9:24   ` Stefan Hajnoczi
2020-06-29 12:23     ` Liu, Yi L
2020-06-30  2:00       ` Tian, Kevin [this message]
2020-06-30  3:45         ` Liu, Yi L
2020-07-03  9:59         ` Stefan Hajnoczi
2020-07-02 17:54   ` Alex Williamson
2020-07-03  3:53     ` Liu, Yi L
2020-06-24  8:55 ` [PATCH v3 03/14] vfio/type1: Report iommu nesting info to userspace Liu Yi L
2020-07-02 18:38   ` Alex Williamson
2020-07-03  6:05     ` Liu, Yi L
2020-07-03 13:03       ` Liu, Yi L
2020-06-24  8:55 ` [PATCH v3 04/14] vfio: Add PASID allocation/free support Liu Yi L
2020-07-02 21:17   ` Alex Williamson
2020-07-03  6:08     ` Liu, Yi L
2020-06-24  8:55 ` [PATCH v3 05/14] iommu/vt-d: Support setting ioasid set to domain Liu Yi L
2020-06-24  8:55 ` [PATCH v3 06/14] vfio/type1: Add VFIO_IOMMU_PASID_REQUEST (alloc/free) Liu Yi L
2020-07-02 21:18   ` Alex Williamson
2020-07-03  6:28     ` Liu, Yi L
2020-07-08  8:16       ` Liu, Yi L
2020-07-08 19:54         ` Alex Williamson
2020-07-09  0:32           ` Liu, Yi L
2020-07-09  1:56             ` Tian, Kevin
2020-07-09  2:08               ` Liu, Yi L
2020-07-09  2:18                 ` Tian, Kevin
2020-07-09  2:26                   ` Liu, Yi L
2020-07-09  7:16                     ` Liu, Yi L
2020-07-09 14:27                       ` Alex Williamson
2020-07-09 18:05                         ` Jacob Pan
2020-07-10  5:39                         ` Liu, Yi L
2020-07-10 12:55                           ` Alex Williamson
2020-07-10 13:03                             ` Liu, Yi L
2020-06-24  8:55 ` [PATCH v3 07/14] iommu: Pass domain to sva_unbind_gpasid() Liu Yi L
2020-06-24  8:55 ` [PATCH v3 08/14] iommu/vt-d: Check ownership for PASIDs from user-space Liu Yi L
2020-06-24  8:55 ` [PATCH v3 09/14] vfio/type1: Support binding guest page tables to PASID Liu Yi L
2020-07-02 21:19   ` Alex Williamson
2020-07-03  6:46     ` Liu, Yi L
2020-06-24  8:55 ` [PATCH v3 10/14] vfio/type1: Allow invalidating first-level/stage IOMMU cache Liu Yi L
2020-07-02 21:19   ` Alex Williamson
2020-07-03  3:47     ` Liu, Yi L
2020-06-24  8:55 ` [PATCH v3 11/14] vfio/type1: Add vSVA support for IOMMU-backed mdevs Liu Yi L
2020-06-24  8:55 ` [PATCH v3 12/14] vfio/pci: Expose PCIe PASID capability to guest Liu Yi L
2020-06-24  8:55 ` [PATCH v3 13/14] vfio: Document dual stage control Liu Yi L
2020-06-29  9:21   ` Stefan Hajnoczi
2020-06-29  9:24     ` Liu, Yi L
2020-06-24  8:55 ` [PATCH v3 14/14] iommu/vt-d: Support reporting nesting capability info Liu Yi L

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