Re: [PATCH v3 3/4] xen/arm: Reserve domid 0 for Dom0

[Julien Grall <julien@xxxxxxx>]

Hi Luca,

The title probably wants to be updated as you don't really reserve domid 
0. How about:
xen/arm: Clarify how the domid is decided in create_domUs()

On 12/04/2021 11:52, Luca Fancellu wrote:
> This patch adds a comment in create_domUs() right before
> domain_create() to explain the importance of the pre-increment
> operator on the variable max_init_domid, to ensure that the
> domid 0 is allocated only during start_xen() function by the
> create_dom0() and not on any other possible code path to the
> domain_create() function.
>
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
> Changes in v3:
> - removed check introduced in v2.
> ---
>   xen/arch/arm/domain_build.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 359957dc1b..b1d7b9849f 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -2508,6 +2508,11 @@ void __init create_domUs(void)
>                                            GUEST_VPL011_SPI - 32 + 1);
>           }
>   
> +        /*
> +         * The variable max_init_domid is initialized with zero, so here it's
> +         * very important to use the pre-increment operator to call
> +         * domain_create() with a domid > 0. (domid == 0 is reserved for Dom0)
> +         */
>           d = domain_create(++max_init_domid, &d_cfg, false);
>           if ( IS_ERR(d) )
>               panic("Error creating domain %s\n", dt_node_name(node));
--
Julien Grall