Re: [PATCH v3 08/15] vfio/common: Relax vIOMMU detection when DMA translation is off

[Philippe Mathieu-Daudé]

On 30/5/23 19:59, Joao Martins wrote:
> Relax the vIOMMU migration blocker when the underlying IOMMU reports that
> DMA translation disabled. When it is disabled there will be no DMA mappings
> via the vIOMMU and the guest only uses it for Interrupt Remapping.
>
> The latter is done via the vfio_viommu_preset() return value whereby in
> addition to validating that the address space is memory, we also check
> whether the IOMMU MR has DMA translation on.

> Assume it is enabled if
> there's no IOMMU MR or if no dma-translation property is supported.

This comment ^ ...

> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
>   hw/vfio/common.c | 22 +++++++++++++++++++++-
>   1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index fa8fd949b1cf..060acccb3443 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -414,12 +414,32 @@ void vfio_unblock_multiple_devices_migration(void)
>       multiple_devices_migration_blocker = NULL;
>   }
>   
> +static bool vfio_viommu_dma_translation_enabled(VFIOAddressSpace *space)
> +{
> +    bool enabled = false;
> +    int ret;
> +
> +    if (!space->iommu_mr) {
> +        return true;
> +    }
> +
> +    ret = memory_region_iommu_get_attr(space->iommu_mr,
> +                                       IOMMU_ATTR_DMA_TRANSLATION,
> +                                       &enabled);
> +    if (ret || enabled) {

... could be helpful if duplicated here.

> +        return true;
> +    }
> +
> +    return false;
> +}