When onlining a new memory page in a guest the Xen balloon driver is adding it to the ballooned pages instead making it available to be used immediately. This is meant to enable to add a new upper memory limit to a guest via hotplugging memory, without having to assign the new memory in one go.
In case the upper memory limit will be raised above 4G, the new memory will populate the ZONE_NORMAL memory zone, which wasn't populated before. The newly populated zone won't be added to the list of zones looked at by the page allocator though, as only zones with available memory are being added, and the memory isn't yet available as it is ballooned out.
This will result in the new memory being assigned to the guest, but without the allocator being able to use it.
When running as a PV guest the situation is even worse: when having been started with less memory than allowed, and the upper limit being lower than 4G, ballooning up will have the same effect as hotplugging new memory. This is due to the usage of the zone device functionality since commit 9e2369c06c8a ("xen: add helpers to allocate unpopulated memory") for creating mappings of other guest's pages, which as a side effect is being used for PV guest ballooning, too.
Fix this by checking in xen_online_page() whether the new memory page will be the first in a new zone. If this is the case, add another page to the balloon and use the first memory page of the new chunk as a replacement for this now ballooned out page. This will result in the newly populated zone containing one page being available for the page allocator, which in turn will lead to the zone being added to the allocator.
Cc: stable@vger.kernel.org Fixes: 9e2369c06c8a ("xen: add helpers to allocate unpopulated memory") Reported-by: Marek Marczykowski-Górecki marmarek@invisiblethingslab.com Signed-off-by: Juergen Gross jgross@suse.com --- drivers/xen/balloon.c | 72 ++++++++++++++++++++++++++++++++++++++----- 1 file changed, 65 insertions(+), 7 deletions(-)
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c index dfe26fa17e95..f895c54c4c65 100644 --- a/drivers/xen/balloon.c +++ b/drivers/xen/balloon.c @@ -355,14 +355,77 @@ static enum bp_state reserve_additional_memory(void) return BP_ECANCELED; }
+static struct page *alloc_page_for_balloon(gfp_t gfp) +{ + struct page *page; + + page = alloc_page(gfp); + if (page == NULL) + return NULL; + + adjust_managed_page_count(page, -1); + xenmem_reservation_scrub_page(page); + + return page; +} + +static void add_page_to_balloon(struct page *page) +{ + xenmem_reservation_va_mapping_reset(1, &page); + balloon_append(page); +} + static void xen_online_page(struct page *page, unsigned int order) { unsigned long i, size = (1 << order); unsigned long start_pfn = page_to_pfn(page); struct page *p; + struct zone *zone;
pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, start_pfn); mutex_lock(&balloon_mutex); + zone = page_zone(pfn_to_page(start_pfn)); + + /* + * In case a new memory zone is going to be populated, we need to + * ensure at least one page is made available for the memory allocator. + * As the number of pages per zone is updated only after a batch of + * pages having been added, use the number of managed pages as an + * additional indicator for a new zone. + * Otherwise this zone won't be added to the zonelist resulting in the + * zone's memory not usable by the kernel. + * Add an already valid page to the balloon and replace it with the + * first page of the to be added new memory chunk. + */ + if (!populated_zone(zone) && !managed_zone(zone)) { + xen_pfn_t frame; + + pr_info("Populating new zone\n"); + + p = alloc_page_for_balloon(GFP_ATOMIC); + if (!p) { + pr_err("Failed to allocate replacement balloon page!\n"); + pr_err("New onlined memory might not be usable.\n"); + } else { + kmap_flush_unused(); + add_page_to_balloon(p); + flush_tlb_all(); + frame = xen_page_to_gfn(p); + xenmem_reservation_decrease(1, &frame); + balloon_stats.current_pages--; + } + + p = pfn_to_page(start_pfn); + frame = page_to_xen_pfn(p); + if (xenmem_reservation_increase(1, &frame) > 0) { + xenmem_reservation_va_mapping_update(1, &p, &frame); + free_reserved_page(p); + balloon_stats.current_pages++; + + start_pfn++; + size--; + } + } for (i = 0; i < size; i++) { p = pfn_to_page(start_pfn + i); balloon_append(p); @@ -452,14 +515,12 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) nr_pages = ARRAY_SIZE(frame_list);
for (i = 0; i < nr_pages; i++) { - page = alloc_page(gfp); + page = alloc_page_for_balloon(gfp); if (page == NULL) { nr_pages = i; state = BP_EAGAIN; break; } - adjust_managed_page_count(page, -1); - xenmem_reservation_scrub_page(page); list_add(&page->lru, &pages); }
@@ -480,11 +541,8 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) list_for_each_entry_safe(page, tmp, &pages, lru) { frame_list[i++] = xen_page_to_gfn(page);
- xenmem_reservation_va_mapping_reset(1, &page); - list_del(&page->lru); - - balloon_append(page); + add_page_to_balloon(page); }
flush_tlb_all();