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From: Paul Durrant <Paul.Durrant@citrix.com>
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	"Tim (Xen.org)" <tim@xen.org>,
	George Dunlap <George.Dunlap@citrix.com>,
	Julien Grall <julien.grall@arm.com>,
	Jan Beulich <jbeulich@suse.com>,
	Ian Jackson <Ian.Jackson@citrix.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v4 01/15] re-work commit 3e06b989 "IOMMU: make page table population preemptible"...
Date: Thu, 2 Aug 2018 10:26:18 +0000	[thread overview]
Message-ID: <136b66bc103148a9b5143467bb29b879@AMSPEX02CL03.citrite.net> (raw)
In-Reply-To: <20180801161517.kg3diasbulao6jei@mac>

> -----Original Message-----
> From: Roger Pau Monne
> Sent: 01 August 2018 17:15
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: xen-devel@lists.xenproject.org; Stefano Stabellini
> <sstabellini@kernel.org>; Wei Liu <wei.liu2@citrix.com>; George Dunlap
> <George.Dunlap@citrix.com>; Andrew Cooper
> <Andrew.Cooper3@citrix.com>; Ian Jackson <Ian.Jackson@citrix.com>; Tim
> (Xen.org) <tim@xen.org>; Julien Grall <julien.grall@arm.com>; Jan Beulich
> <jbeulich@suse.com>
> Subject: Re: [Xen-devel] [PATCH v4 01/15] re-work commit 3e06b989
> "IOMMU: make page table population preemptible"...
> 
> On Wed, Aug 01, 2018 at 02:40:14PM +0100, Paul Durrant wrote:
> > ...to simplify the implementation and turn need_iommu back into a
> boolean.
> >
> > As noted in [1] the tri-state nature of need_iommu after commit 3e06b989
> is
> > confusing, as is the implementation of pre-emption using relmem_list.
> >
> > This patch instead uses a simple count of pages already populated stored in
> > the x86 variant of struct arch_iommu and skips over that number of pages
> > if arch_iommu_populate_page_table() is re-invoked after pre-emption.
> 
> Urg, all this is quite ugly. It would be quite better if the need for
> an IOMMU was decided before populating the p2m (ie: at domain_create
> time by passing an extra XEN_DOMCTL_CDF_iommu or some such), so that
> the normal addition of RAM would also populate the IOMMU page tables
> if not shared.

Given the problems that Jan has highlighted with using a skip count and essentially being forced to mess with the domain's page list, I think your suggestion is best. Then we can entirely bin arch_iommu_populate_page_table(). That is a bigger piece of work though so in the interest of no blocking the rest of this series I'll drop this patch and replace it with a simpler patch that's just sufficient to make need_iommu boolean again.

  Paul

> 
> > [1] https://lists.xenproject.org/archives/html/xen-devel/2018-
> 07/msg01870.html
> >
> > Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> 
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
> 
> Thanks, Roger.

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  reply	other threads:[~2018-08-02 10:26 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-01 13:40 [PATCH v4 00/15] paravirtual IOMMU interface Paul Durrant
2018-08-01 13:40 ` [PATCH v4 01/15] re-work commit 3e06b989 "IOMMU: make page table population preemptible" Paul Durrant
2018-08-01 16:15   ` Roger Pau Monné
2018-08-02 10:26     ` Paul Durrant [this message]
2018-08-02  7:19   ` Jan Beulich
2018-08-02  8:02     ` Paul Durrant
2018-08-02  8:04       ` Paul Durrant
2018-08-02  8:18         ` Jan Beulich
2018-08-02  8:49           ` Paul Durrant
2018-08-02 10:01             ` Jan Beulich
2018-08-01 13:40 ` [PATCH v4 02/15] iommu: introduce the concept of BFN Paul Durrant
2018-08-01 13:40 ` [PATCH v4 03/15] iommu: make use of type-safe BFN and MFN in exported functions Paul Durrant
2018-08-01 13:40 ` [PATCH v4 04/15] iommu: push use of type-safe BFN and MFN into iommu_ops Paul Durrant
2018-08-01 13:40 ` [PATCH v4 05/15] iommu: don't domain_crash() inside iommu_map/unmap_page() Paul Durrant
2018-08-01 13:40 ` [PATCH v4 06/15] public / x86: introduce __HYPERCALL_iommu_op Paul Durrant
2018-08-01 13:40 ` [PATCH v4 07/15] iommu: track reserved ranges using a rangeset Paul Durrant
2018-08-01 13:40 ` [PATCH v4 08/15] x86: add iommu_op to query reserved ranges Paul Durrant
2018-08-01 13:40 ` [PATCH v4 09/15] vtd: add lookup_page method to iommu_ops Paul Durrant
2018-08-01 13:40 ` [PATCH v4 10/15] mm / iommu: include need_iommu() test in iommu_use_hap_pt() Paul Durrant
2018-08-01 13:40 ` [PATCH v4 11/15] mm / iommu: split need_iommu() into has_iommu_pt() and sync_iommu_pt() Paul Durrant
2018-08-01 13:40 ` [PATCH v4 12/15] x86: add iommu_op to enable modification of IOMMU mappings Paul Durrant
2018-08-01 13:40 ` [PATCH v4 13/15] memory: add get_paged_gfn() as a wrapper Paul Durrant
2018-08-01 13:40 ` [PATCH v4 14/15] x86: add iommu_ops to modify and flush IOMMU mappings Paul Durrant
2018-08-01 13:40 ` [PATCH v4 15/15] x86: extend the map and unmap iommu_ops to support grant references Paul Durrant

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