[PATCH v5 3/7] xen/evtchn: restrict the maximum number of evtchn supported for domUs

[Rahul Singh <rahul.singh@xxxxxxx>]

Restrict the maximum number of evtchn supported for domUs to avoid
allocating a large amount of memory in Xen.

Set the default value of max_evtchn_port to 1023. The value of 1023
should be sufficient for guests because on ARM we don't bind physical
interrupts to event channels. The only use of the evtchn port is
inter-domain communications. Another reason why we choose the value
of 1023 is to follow the default behavior of libxl.

Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
---
Changes in v5:
 - fix minor comments
 - Added Julien Acked-by
Changes in v4:
 - fix minor comments in commit msg
 - Added Michal Reviewed-by
Changes in v3:
 - added in commit msg why we set the max_evtchn_port value to 1023.
 - added the comment in code also why we set the max_evtchn_port to 1023
 - remove the define and set the value to 1023 in code directly.
Changes in v2:
 - new patch in the version
---
 xen/arch/arm/domain_build.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index b76a84e8f5..e1f46308d9 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -3277,7 +3277,13 @@ void __init create_domUs(void)
         struct xen_domctl_createdomain d_cfg = {
             .arch.gic_version = XEN_DOMCTL_CONFIG_GIC_NATIVE,
             .flags = XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap,
-            .max_evtchn_port = -1,
+            /*
+             * The default of 1023 should be sufficient for guests because
+             * on ARM we don't bind physical interrupts to event channels.
+             * The only use of the evtchn port is inter-domain communications.
+             * 1023 is also the default value used in libxl.
+             */
+            .max_evtchn_port = 1023,
             .max_grant_frames = -1,
             .max_maptrack_frames = -1,
             .grant_opts = XEN_DOMCTL_GRANT_version(opt_gnttab_max_version),
-- 
2.25.1