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From: "Jan Beulich" <JBeulich@suse.com>
To: Paul Durrant <paul.durrant@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>, Tim Deegan <tim@xen.org>,
	Julien Grall <julien.grall@arm.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v4 01/15] re-work commit 3e06b989 "IOMMU: make page table population preemptible"...
Date: Thu, 02 Aug 2018 01:19:54 -0600	[thread overview]
Message-ID: <5B62B09A02000078001DA278@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <20180801134028.1654-2-paul.durrant@citrix.com>

>>> On 01.08.18 at 15:40, <paul.durrant@citrix.com> 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.

Well, yes, I would have used that model in said commit if it was reliable,
but it isn't: What if the list of pages changed between two (re-)invocations?
Furthermore, with huge enough a guest even the skipping of the already
processed several million pages may exhaust the time acceptable between
preemption points.

Jan



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  parent reply	other threads:[~2018-08-02  7:19 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
2018-08-02  7:19   ` Jan Beulich [this message]
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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