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Re: [PATCH v2 1/2] vfio: Allow No-IOMMU mode without checking iommu_present()

From Will Deacon <will.deacon@arm.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2 1/2] vfio: Allow No-IOMMU mode without checking iommu_present()
Date 2017-07-20 11:20 +0200
Message-ID <u5fMK-5hG-27@gated-at.bofh.it> (permalink)
References <u5bpL-28h-3@gated-at.bofh.it> <u5bpL-28h-5@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Thu, Jul 20, 2017 at 10:02:33AM +0530, Anup Patel wrote:
> Not allowing No-IOMMU mode for devices already having
> iommu_ops on their bus is very conservative.
> 
> We now have IOMMU (such as ARM SMMU) which can bypass
> transcations when IOMMU is not configured for a given
> device. In addition, it is not necessary to have all
> devices on bus to be upstream to an IOMMU on that bus.

How does the SMMU know to bypass in these cases? As I explained before, the
driver-specific command line option is the wrong way to go about arranging
this.

Will

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Thread

[PATCH v2 1/2] vfio: Allow No-IOMMU mode without checking iommu_present() Anup Patel <anup.patel@broadcom.com> - 2017-07-20 06:40 +0200
  Re: [PATCH v2 1/2] vfio: Allow No-IOMMU mode without checking  iommu_present() Will Deacon <will.deacon@arm.com> - 2017-07-20 11:20 +0200
  Re: [PATCH v2 1/2] vfio: Allow No-IOMMU mode without checking  iommu_present() Alex Williamson <alex.williamson@redhat.com> - 2017-07-24 19:30 +0200

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