From b13cd24c15d74f6dfcddf0d53ae6efb58d3f0461 Mon Sep 17 00:00:00 2001 From: Roger Pau Monne Date: Wed, 28 Jan 2026 12:05:09 +0100 Subject: [PATCH] xen/balloon: improve accuracy of initial balloon target for dom0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The dom0 balloon target set by the toolstack is the value returned by XENMEM_current_reservation. Do the same in the kernel balloon driver and set the current allocation to the value returned by XENMEM_current_reservation. On my test system this causes the kernel balloon driver target to exactly match the value set by the toolstack in xenstore. Note this approach can be used by both PV and PVH dom0s, as the toolstack always uses XENMEM_current_reservation to set the initial target regardless of the dom0 type. Signed-off-by: Roger Pau Monné Reviewed-by: Juergen Gross Signed-off-by: Juergen Gross Message-ID: <20260128110510.46425-3-roger.pau@citrix.com> --- drivers/xen/balloon.c | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-) diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index 8c44a25a7d2b9..9b6531eb28b65 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -724,7 +724,8 @@ static int __init balloon_add_regions(void) static int __init balloon_init(void) { struct task_struct *task; - unsigned long current_pages; + long current_pages = 0; + domid_t domid = DOMID_SELF; int rc; if (!xen_domain()) @@ -732,15 +733,21 @@ static int __init balloon_init(void) pr_info("Initialising balloon driver\n"); - if (xen_pv_domain()) { - if (xen_released_pages >= xen_start_info->nr_pages) - goto underflow; - current_pages = min(xen_start_info->nr_pages - - xen_released_pages, max_pfn); - } else { - if (xen_unpopulated_pages >= get_num_physpages()) - goto underflow; - current_pages = get_num_physpages() - xen_unpopulated_pages; + if (xen_initial_domain()) + current_pages = HYPERVISOR_memory_op(XENMEM_current_reservation, + &domid); + if (current_pages <= 0) { + if (xen_pv_domain()) { + if (xen_released_pages >= xen_start_info->nr_pages) + goto underflow; + current_pages = min(xen_start_info->nr_pages - + xen_released_pages, max_pfn); + } else { + if (xen_unpopulated_pages >= get_num_physpages()) + goto underflow; + current_pages = get_num_physpages() - + xen_unpopulated_pages; + } } balloon_stats.current_pages = current_pages; -- 2.47.3