Re: [Xen-devel] [RFC PATCH 3/3] tools, libxl: handle the iomem parameter with the memory_mapping hcall

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hello Arianna,

Adding Ian Jackson, maintainer of libxl.

On 02/03/14 08:49, Arianna Avanzini wrote:
> Currently, the configuration-parsing code concerning the handling of the
> iomem parameter only invokes the XEN_DOMCTL_iomem_permission hypercall.
> This commit lets the XEN_DOMCTL_memory_mapping hypercall be invoked
> after XEN_DOMCTL_iomem_permission when the iomem parameter is parsed
> from a domU configuration file.
Do you plan to give I/O mem range which is not describe by the device tree?

IHMO, allow the user to specify which I/O mem region will be mapped to 
the guest on ARM is wrong. As the platform is described via the device 
tree, the guest configuration should have a list of node to map to domU. 
Then {lib,}xl will parse/map/update the DT node to the guest.
> Signed-off-by: Arianna Avanzini <avanzini.arianna@xxxxxxxxx>
> Cc: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> Cc: Paolo Valente <paolo.valente@xxxxxxxxxx>
> Cc: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxxxxx>
> Cc: Eric Trudeau <etrudeau@xxxxxxxxxxxx>
> Cc: Viktor Kleinik <viktor.kleinik@xxxxxxxxxxxxxxx>
> ---
>   tools/libxl/libxl_create.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
> index a604cd8..7da0778 100644
> --- a/tools/libxl/libxl_create.c
> +++ b/tools/libxl/libxl_create.c
> @@ -1099,6 +1099,16 @@ static void domcreate_launch_dm(libxl__egc *egc, 
> libxl__multidev *multidev,
>                    "failed give dom%d access to iomem range %"PRIx64"-%"PRIx64,
>                    domid, io->start, io->start + io->number - 1);
>               ret = ERROR_FAIL;
> +        } else {
> +            ret = xc_domain_memory_mapping(CTX->xch, domid,
> +                                           io->start, io->start,
> +                                           io->number, 1);
> +            if (ret < 0) {
> +                LOGE(ERROR,
> +                     "failed to map to dom%d iomem range %"PRIx64"-%"PRIx64,
> +                     domid, io->start, io->start + io->number - 1);
> +                ret = ERROR_FAIL;
> +            }
This code is common on both x86 and ARM. On x86, we don't want to map
the I/O mem region in the guest here. QEMU will do it later.

The 1:1 mapping doesn't seem correct because the range could clash with 
the guest layout (e.g: GIC base address, RAM base address) which is for 
now hardcoded (see xen/include/public/arch-arm.h:358).
I have various solution to fix this issue:
  - Relocate the GIC/RAM base address and notify Xen that the GIC base 
address has changed. So we can keep the 1:1 mapping.
  - Let libxl decide where to map the I/O mem range in the guest.

For the latter solution, we will have to find a way to tell to the guest 
: "This I/O mem range is here ...". Perhaps via the device tree.
Regards,

--
Julien Grall

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