Re: [PATCH v2 8/8] docs: Add '-device virtio-iommu' entry

From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: peter.maydell@linaro.org, ehabkost@redhat.com, mst@redhat.com,
	richard.henderson@linaro.org, qemu-devel@nongnu.org,
	eric.auger@redhat.com, shannon.zhaosl@gmail.com,
	qemu-arm@nongnu.org, imammedo@redhat.com, pbonzini@redhat.com
Subject: Re: [PATCH v2 8/8] docs: Add '-device virtio-iommu' entry
Date: Mon, 6 Sep 2021 15:45:28 +0100	[thread overview]
Message-ID: <YTYpiPYaRJHmCmsK@redhat.com> (raw)
In-Reply-To: <20210903143208.2434284-9-jean-philippe@linaro.org>

On Fri, Sep 03, 2021 at 04:32:09PM +0200, Jean-Philippe Brucker wrote:
> Document the virtio-iommu device for qemu-system-x86_64. In particular
> note the lack of interrupt remapping, which may be an important
> limitation on x86.
> 
> Suggested-by: Eric Auger <eric.auger@redhat.com>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
>  qemu-options.hx | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 83aa59a920..9a1906a748 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -976,6 +976,9 @@ SRST
>      Please also refer to the wiki page for general scenarios of VT-d
>      emulation in QEMU: https://wiki.qemu.org/Features/VT-d.
>  
> +``-device virtio-iommu``
> +    Enable a paravirtual IOMMU, that manages DMA isolation and remapping
> +    for all PCI devices, but does not support interrupt remapping.

It would be desirable to document why this is better/worse/equiv to
the intel-iommu device documented just before, so that people have a
better idea of which they should be trying to use.

I'm going to assume intel-iommu is more likely to "just work" out of
the box since it models real hardware that OS are likely to already
support ?  Is that right though ?

Regards,
Daniel
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