linux-kernel - Re: [PATCH v3 02/14] iommu: Report domain nesting info

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200703095902.GA178149@stefanha-x1.localdomain>
Date:   Fri, 3 Jul 2020 10:59:02 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "Wu, Hao" <hao.wu@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 02/14] iommu: Report domain nesting info

On Tue, Jun 30, 2020 at 02:00:49AM +0000, Tian, Kevin wrote:
> > From: Liu, Yi L <yi.l.liu@...el.com>
> > Sent: Monday, June 29, 2020 8:23 PM
> > 
> > Hi Stefan,
> > 
> > > From: Stefan Hajnoczi <stefanha@...il.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.
> --

Mentioning the API to allocate/free PASIDs and VFIO_IOMMU_NESTING_OP has
made this clearer. This lets someone reading the documentation know
where to look for further information on using these features.

Thank you!

Stefan

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)