xen/balloon: don't alloc page while non-preemptible

get_balloon_scratch_page() disables preemption so we cannot call
alloc_page() in between get/put_balloon_scratch_page().  Shuffle bits
around in decrease_reservation() to avoid this.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 11 insertions, 12 deletions

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index a50c6e3a7cc4..b232908a6192 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -398,8 +398,6 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
         if (nr_pages > ARRAY_SIZE(frame_list))
                 nr_pages = ARRAY_SIZE(frame_list);
 
-        scratch_page = get_balloon_scratch_page();
-
         for (i = 0; i < nr_pages; i++) {
                 page = alloc_page(gfp);
                 if (page == NULL) {
@@ -413,6 +411,12 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
 
                 scrub_page(page);
 
+                /*
+                 * Ballooned out frames are effectively replaced with
+                 * a scratch frame.  Ensure direct mappings and the
+                 * p2m are consistent.
+                 */
+                scratch_page = get_balloon_scratch_page();
 #ifdef CONFIG_XEN_HAVE_PVMMU
                 if (xen_pv_domain() && !PageHighMem(page)) {
                         ret = HYPERVISOR_update_va_mapping(
@@ -422,24 +426,19 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
                         BUG_ON(ret);
                 }
 #endif
-        }
-
-        /* Ensure that ballooned highmem pages don't have kmaps. */
-        kmap_flush_unused();
-        flush_tlb_all();
-
-        /* No more mappings: invalidate P2M and add to balloon. */
-        for (i = 0; i < nr_pages; i++) {
-                pfn = mfn_to_pfn(frame_list[i]);
                 if (!xen_feature(XENFEAT_auto_translated_physmap)) {
                         unsigned long p;
                         p = page_to_pfn(scratch_page);
                         __set_phys_to_machine(pfn, pfn_to_mfn(p));
                 }
+                put_balloon_scratch_page();
+
                 balloon_append(pfn_to_page(pfn));
         }
 
-        put_balloon_scratch_page();
+        /* Ensure that ballooned highmem pages don't have kmaps. */
+        kmap_flush_unused();
+        flush_tlb_all();
 
         set_xen_guest_handle(reservation.extent_start, frame_list);
         reservation.nr_extents   = nr_pages;