Re: [Xen-devel] [PATCH v7 7/8] xen/arm: export shared memory regions as reserved-memory on device tree

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 11/08/18 01:00, Stefano Stabellini wrote:
> Shared memory regions need to be advertised to the guest. Fortunately, a
> device tree binding for special memory regions already exist:
> reserved-memory.
>
> Add a reserved-memory node for each shared memory region, for both
> masters and slaves.
>
> Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> ---
> Changes in v7:
> - change node name to xen-shmem
> - add compatible property
> - add id property
> ---
>   tools/libxl/libxl_arch.h |  2 +-
>   tools/libxl/libxl_arm.c  | 59 +++++++++++++++++++++++++++++++++++++++++++++---
>   tools/libxl/libxl_dom.c  |  2 +-
>   tools/libxl/libxl_x86.c  |  2 +-
>   4 files changed, 59 insertions(+), 6 deletions(-)
>
> diff --git a/tools/libxl/libxl_arch.h b/tools/libxl/libxl_arch.h
> index 6a07ccf..3626e4a 100644
> --- a/tools/libxl/libxl_arch.h
> +++ b/tools/libxl/libxl_arch.h
> @@ -36,7 +36,7 @@ int libxl__arch_domain_create(libxl__gc *gc, 
> libxl_domain_config *d_config,
>   /* setup arch specific hardware description, i.e. DTB on ARM */
>   _hidden
>   int libxl__arch_domain_init_hw_description(libxl__gc *gc,
> -                                           libxl_domain_build_info *info,
> +                                           libxl_domain_config *d_config,
>                                              libxl__domain_build_state *state,
>                                              struct xc_dom_image *dom);
>   /* finalize arch specific hardware description. */
> diff --git a/tools/libxl/libxl_arm.c b/tools/libxl/libxl_arm.c
> index 5f62e78..72dd0d2 100644
> --- a/tools/libxl/libxl_arm.c
> +++ b/tools/libxl/libxl_arm.c
> @@ -461,6 +461,56 @@ static int make_memory_nodes(libxl__gc *gc, void *fdt,
>       return 0;
>   }
>   
> +static int make_reserved_nodes(libxl__gc *gc, void *fdt,
> +                               libxl_domain_config *d_config)
> +{
> +    int res, i;
> +    const char *name;
> +
> +    if (d_config->num_sshms == 0)
> +        return 0;
> +
> +    res = fdt_begin_node(fdt, "reserved-memory");
> +    if (res) return res;
> +
> +    res = fdt_property_cell(fdt, "#address-cells", ROOT_ADDRESS_CELLS);
> +    if (res) return res;
> +
> +    res = fdt_property_cell(fdt, "#size-cells", ROOT_SIZE_CELLS);
> +    if (res) return res;
> +
> +    res = fdt_property(fdt, "ranges", NULL, 0);
> +    if (res) return res;
> +
> +    for (i = 0; i < d_config->num_sshms; i++) {
> +        uint64_t start = d_config->sshms[i].begin;
NIT: newline.

> +        if (d_config->sshms[i].role == LIBXL_SSHM_ROLE_SLAVE)
> +            start += d_config->sshms[i].offset;
> +        name = GCSPRINTF("xen-shmem@%"PRIx64, start);
> +
> +        res = fdt_begin_node(fdt, name);
> +        if (res) return res;
> +
> +        res = fdt_property_regs(gc, fdt, ROOT_ADDRESS_CELLS, ROOT_SIZE_CELLS,
> +                                1, start, d_config->sshms[i].size);
> +        if (res) return res;
> +
> +        res = fdt_property_compat(gc, fdt, 1, "xen,shared-memory");
This requires a patch in the Linux DT docs for the new binding. But more 
likely you want to expose a bit more about the shared-memory. For 
instance the ID is something really useful to have in hand.
This could help a tailored guest to distinguish between 2 shared memory.

Cheers,

--
Julien Grall

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