[xen staging] xen/arm: Clarify how the domid is decided in create_domUs()

[patchbot@xxxxxxx]

commit b3d1f523c8de3a6657b11456a56bd8f5e67e247b
Author:     Luca Fancellu <luca.fancellu@xxxxxxx>
AuthorDate: Wed Apr 14 10:14:03 2021 +0100
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Thu Apr 15 18:08:29 2021 +0100

    xen/arm: Clarify how the domid is decided in create_domUs()
    
    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>
    Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
    Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
---
 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));
--
generated by git-patchbot for /home/xen/git/xen.git#staging