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Re: [PATCH v4 3/4] xen/arm: Clarify how the domid is decided in create_domUs()





On 14/04/2021 10:14, 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>

Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

---
Changes in v4:
- Change to the commit title
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



 


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