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.
 ERST
 
 DEF("name", HAS_ARG, QEMU_OPTION_name,
-- 
2.33.0

Hi Jean,

On 9/3/21 4:32 PM, Jean-Philippe Brucker wrote:
> Document the virtio-iommu device for qemu-system-x86_64. In particular
Nit: this is not only for qemu-system-x86_6. This also documents the
option usage for aarch64. Only the interrupt remapping note is x86-64
specific.

I think it also would be worth to mention the interaction with the
bypass iommu option as you mention "for all devices".

Thanks

Eric
> 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.
>  ERST
>  
>  DEF("name", HAS_ARG, QEMU_OPTION_name,

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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Hi,

On 9/3/21 4:32 PM, 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.
maybe you should also document which machines do support the
virtio-iommu (as done for intel-iommu). By the way intel-iommu only is
supported on q35. Is it the same for the virtio-iommu. I think we should
restrict the virtio-iommu to q35 too

Thanks

Eric
>  ERST
>  
>  DEF("name", HAS_ARG, QEMU_OPTION_name,