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Re: [Qemu-devel] [PATCH 0/2] memory/intel_iommu: Generate error for inco

From: Alexey Kardashevskiy
Subject: Re: [Qemu-devel] [PATCH 0/2] memory/intel_iommu: Generate error for incompatible usage
Date: Thu, 16 Jun 2016 11:43:46 +1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.0

On 16/06/16 01:56, Alex Williamson wrote:
> VT-d emulation is currently incompatible with device assignment due
> to intel_iommu's lack of support for memory_region_notify_iommu().
> Alexey has proposed a nice addition to the MemoryRegionIOMMUOps
> structure that adds callbacks when the first iommu notifier is
> registered and the last is removed.  For POWER this will allow them
> to switch the view of the iommu depending on whether anyone in
> userspace is watching.  For VT-d I expect that eventually we'll use
> these callbacks to enable and disable code paths so that we avoid
> notifier overhead when there are no registered notifiy-ees.  For now,
> we don't support calling memory_region_notify_iommu(), so this
> signals an incompatible hardware configuration.  If we choose to make
> CM=0 a user selectable option, something like this might continue to
> be useful if we only support notifies via invalidations rather than
> full VT-d data structure shadowing.
> Even though we're currently working on enabling users like vfio-pci
> with VT-d, I believe this is correct for the current state of things.
> We might even want to consider this stable for v2.6.x so that
> downstreams pick it up to avoid incompatible configurations.
> Alexey, I hope I'm not stepping on your toes by extracting this
> from your latest patch series.  Please let us know whether you
> approve.  Thanks,

I am totally fine with either way of accepting my patches, after all the
idea was yours, I just put it in the code :)

> Alex
> ---
> Alex Williamson (1):
>       intel_iommu: Throw hw_error on notify_started
> Alexey Kardashevskiy (1):
>       memory: Add MemoryRegionIOMMUOps.notify_started/stopped callbacks
>  hw/i386/intel_iommu.c |   12 ++++++++++++
>  hw/vfio/common.c      |    5 +++--
>  include/exec/memory.h |    8 +++++++-
>  memory.c              |   10 +++++++++-
>  4 files changed, 31 insertions(+), 4 deletions(-)


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