On 10/24/2017 04:10 AM, Juergen Gross wrote:
> Commit 96edd61dcf44362d3ef0bed1a5361e0ac7886a63 ("xen/balloon: don't
> online new memory initially") introduced a regression when booting a
> HVM domain with memory less than mem-max: instead of ballooning down
> immediately the system would try to use the memory up to mem-max
> resulting in Xen crashing the domain.
>
> For HVM domains the current size will be reflected in Xenstore node
> memory/static-max instead of memory/target.
>
> Additionally we have to trigger the ballooning process at once.
>
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.13
> Fixes: 96edd61dcf44362d3ef0bed1a5361e0ac7886a63 ("xen/balloon: don't
> online new memory initially")
>
> Suggested-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Reported-by: HW42 <hw42@xxxxxxxxx>
> ---
> drivers/xen/xen-balloon.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/xen/xen-balloon.c b/drivers/xen/xen-balloon.c
> index e89136ab851e..3745748d9644 100644
> --- a/drivers/xen/xen-balloon.c
> +++ b/drivers/xen/xen-balloon.c
> @@ -57,7 +57,7 @@ static int register_balloon(struct device *dev);
> static void watch_target(struct xenbus_watch *watch,
> const char *path, const char *token)
> {
> - unsigned long long new_target;
> + unsigned long long new_target, static_max;
> int err;
> static bool watch_fired;
> static long target_diff;
> @@ -72,13 +72,19 @@ static void watch_target(struct xenbus_watch *watch,
> * pages. PAGE_SHIFT converts bytes to pages, hence PAGE_SHIFT - 10.
> */
> new_target >>= PAGE_SHIFT - 10;
> - if (watch_fired) {
> - balloon_set_new_target(new_target - target_diff);
> - return;
> +
> + if (!watch_fired) {
> + watch_fired = true;
> + err = xenbus_scanf(XBT_NIL, "memory", "static-max", "%llu",
> + &static_max);
> + if (err != 1)
> + static_max = new_target;
> + static_max >>= PAGE_SHIFT - 10;
if you set static_max to new_target you've already done the shift,
haven't you?
> + target_diff = xen_pv_domain() ? 0
Why do we special-case PV?
-boris
> + : static_max - balloon_stats.target_pages;
> }
>
> - watch_fired = true;
> - target_diff = new_target - balloon_stats.target_pages;
> + balloon_set_new_target(new_target - target_diff);
> }
> static struct xenbus_watch target_watch = {
> .node = "memory/target",