Re: [RFC 1/1] xen/arm: set iommu property for IOMMU-protected devices

[Oleksandr <olekstysh@xxxxxxxxx>]

On 04.10.21 12:54, Roman Skakun wrote:

Hi Roman

> From: Roman Skakun <roman_skakun@xxxxxxxx>
>
> Xen is not exposing any IOMMU properties to Dom0.
> So Dom0 assumes that all it's devices are not protected by IOMMU.
>
> To make Dom0 aware of IOMMU-protected devices, we need to mark
> them somehow. With this approach Dom0 Linux kernel will be able
> to selectively disable swiotlb-xen fops for them which will remove
> unnecessary buffer bounces.
>
> This patch adds mechanism to describe IOMMU-protected devices by
> adding `xen,behind-iommu` property to relevant device nodes in
> Dom0 device tree.
I think that new property should be documented probably at

docs/misc/arm/device-tree/...

> Signed-off-by: Roman Skakun <roman_skakun@xxxxxxxx>
> ---
>   xen/arch/arm/domain_build.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 69fff7fc29..99e2c42b6c 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -580,6 +580,13 @@ static int __init write_properties(struct domain *d, 
> struct kernel_info *kinfo,
>               return res;
>       }
>   
> +    if ( iommu_node && is_iommu_enabled(d) && dt_device_is_protected(node) )
> +    {
> +        res = fdt_property(kinfo->fdt, "xen,behind-iommu", NULL, 0);
> +        if ( res )
> +            return res;
> +    }
> +
>       /*
>        * Override the property "status" to disable the device when it's
>        * marked for passthrough.
--
Regards,

Oleksandr Tyshchenko